Zhigang Lai

Lixin Li
email: lilixinsky@163.com

Ping ' An Liu

Design of limb for parallel mechanism based on screw theory 1

Keywords: parallel mechanism, screw theory, limb, geometric conditions

Based on the reciprocal relationship of twist and wrench in screw theory, the mathematical model for limb of parallel manipulator is established in this paper. According to the motion modes of mobile platform (translation or rotation), we concluded the geometric conditions which the prismatic joint or revolute joint must meet with by analyzing the constraint screw on the platform, which provides the background for development of parallel mechanism.

Introduction

In recent year, since parallel mechanism can offer higher stiffness and larger load capability than those of serial mechanism, it has become a hot research topic in international robotics area. However, it is very difficult to design because of the complexity of kinematics and dynamics, the diversity of limb and the coupling of architecture.

It is the most important task to meet with the DOF of the required motion for designing the parallel mechanism. In fact, DOF is the outward feature. The key is the design of constraint to implement the DOF of the required motion. The DOF of motion is objective in the limb. However, the constraint is designed in the limb by designer. And there are strict requirements to the geometric conditions which the prismatic joint or revolute joint must meet with in the limb.

Based on the reciprocal relationship, in this paper, we concluded the geometric conditions which the prismatic joint or revolute joint must meet with in the limb by analyzing the constraint screw on the platform. According to the limb, we can design the parallel mechanism which is satisfied the required movement. It is a common method to [START_REF] Ball | A Treatise on the Theory of Screws[END_REF] the basic design of the parallel mechanism.

2.Structural synthesis of the constraint screw on the platform

Each limb should provide a constraint screw for the moving platform in the parallel mechanism. According to the constraint characteristics provided to the platform, screw can be divided into twist and wrench. An arbitrary motion screw in space can include six motions at most, three translations along the X, Y, Z axes and three rotations around the X, Y, Z axes.

Twist should provide constraint for movement in space. It can be defined as Twist and wrench are decided by the structural conditions of limb in parallel mechanism. So the type of constraint depends on the structural conditions of limb. According to the type of constraint, we can obtain the characteristic of limb structural. According to the difference of constraint in the limb, they can be divided into unconstrained limb , single constrained limb , double constrained limb , threeconstrained limb,four-constrained limb,five-constrained limb and six-constrained limb. However, the five-constrained limb and six-constrained limb belong to planar limb which have no requirement in the space.

This paper analyzes the limb types including: the limb providing only one twist, the limb with two twists , the limb with three twists; the limb with only one wrench,the limb with two wrenches,the limb with three wrenches; the limb with one twist and one wrench,the limb with two twists and one wrench,the limb with one twist and two wrenches.

The limb with only one twist

The basic expression of screw is$ r ( ; ) r r r s r s = × . It is known from the reciprocal of screw that the limb should consist of the five independent screws which are reciprocal with the twist When the joint is revolute $ ( ;

) s r s = × $ $ r ( ) ( ) [( ) ] r r r r r s r s s r s s r r s 0 × + × = - = × = i i i
According to the geometric feature of vector, it should be known that there is a common perpendicular among 、 r s r r r and s , that is to say, the axis direction of the revolute joint and the axis direction of twist must be in the same plane.

When the joint is prismatic $ (0; )

s = $ $ r 0 r s s = = i
According to the geometric feature of vector, it should be known that and r s s must be perpendicular each other, that is to say, the moving direction of the prismatic joint and the axis direction of twist must be perpendicular each other.

When the structural conditions of limb meet with the above requirements, the limb should provide only one twist. According to the requirements above, we should put up the limb-RRPRR shown as Fig 1 . First, we construct two parallel revolute joints, which make sure the direction of twist. Second, we establish the moving direction of the prismatic joint and the axis direction of twist must be vertical each other. Last, the axis direction of the last two revolute joints must intersect at o point which is the point of action of .

⎧ ⎪ ⎨ ⎪ ⎩
When the joint is revolute $ ( ;

) s r s = × $ $ 1 r 1 1 1 1 1 ( ) ( ) [( ) ] r r r r r s r s s r s s r r s = 0 × + × = -× = i i i ⎧ ⎪ ⎨ ⎪ ⎩ $ $ 2 2 2 2 2 2 ( ) ( ) [( ) ] r r r r r s r s s r s s r r s = 0 × + × = -× = i i i r
According to the geometric feature of vector, it is known that there is a common perpendicular among s 、 s , that is to say, the axis direction of the revolute joint must pass the point which is the point of intersection with the two twists or be parallel the plane which makes sure by the two twists.

When the joint is prismatic $ (0; )

s = $ $ 1 r 1 0 r s s = = i ⎧ ⎪ ⎨ ⎪ ⎩ $ $ 2 r 2 0 r s s = = i
According to the geometric feature of vector, it should be known that and 1 r s s must be vertical each other; and 2 r s s must be vertical each other, that is to say, the moving direction of the prismatic joint must be parallel the cross-produce of the two twists. And there is the only prismatic joint in the limb.

When the structural conditions of limb meet with the above requirements, the limb should provide two twists. According to the requirements above, we should put up the limb-RRPR shown as

The limb with three twists

The basic expression of screw is

$ 1 r 1 1 1 ( ; ) r r r s r s = × $ 2 r 2 2 2 ( ; r r r s r s ) = × $ 3 r 3 3 3 ( ; r r r s r s ) = ×
The limb should provide three independence twists which intersected at a point for platform. The limb constrained the three directions moving of the platform, that is to say, the platform just can be round the point to revolve. The limb should consist of three revolute joints, and that, there is only one type of the limb-RRR. According to the requirements above, we should put up the limb-RRR shown as Fig. 3. When the joint is revolute $ ( ;

⎧ ⎪ ⎪ ⎨ ⎪ ⎪ ⎩
) s r s = × $ $ r 0 r s s = = i
According to the geometric feature of vector, it should be known that and must be vertical each other, that is to say, the axis direction of the revolute joint and the axis direction of wrench must be vertical each other.

r s s

When the joint is prismatic $ (0; )

s = $ $ r 0 =
The equation is satisfied under any conditions, that is to say, the moving direction of the prismatic joint is independent of the axis direction of wrench.

When the structural conditions of limb meet with the requirements above, the limb should provide only one wrench. According to the requirements above, we should put up the limb-RRPRP show as Fig. 4. When the joint is revolute $ ( ;

) s r s = × $ $ 1 r 1 0 r s s = = i $ $ 2 r 2 0 r s s = = i ⎧ ⎪ ⎨ ⎪ ⎩
According to the geometric feature of vector, it should be known that and must be vertical each other;

and must be vertical each other, that is to say, the axis direction of the revolute joint must be parallel the cross-produce of the two wrenches. When the joint is prismatic $ (0; )

s = $ $ 1 r 0 = ⎧ ⎪ ⎨ ⎪ ⎩ $ $ 2 r 0 =
The equation is satisfied under any conditions, that is to say, the moving direction of the prismatic joint is independent of the axis direction of the wrenches.

When the structural conditions of limb meet with the requirements above, the limb should provide only one wrench. According to the requirements above, we should put up the limb-RRPR shown as Fig. 5. Fig. 5. Structur of Limb RRPR-2M (s r1 ×s r2 //s 1 //s 2 //s 3 )

The limb with three wrenches

The basic expression of screw is

$ 1 r 1 (0; ) r s = $ 2 r 2 (0; ) r s = $ 3 r 3 (0; ) r s = ⎧ ⎪ ⎨ ⎪ ⎩
The limb should provide three independence wrenches which are independent each other. The limb constrained the three directions rotation of the platform, that is to say, the platform just can move along the X, Y, Z axis. The limb should consist of three independent prismatic joints, and that, there is only one type of the limb-PPP shown as Fig. 6.

⎧ ⎪ ⎨ ⎪ ⎩ When the joint is revolute $ ( ; ) s r s = × $ $ 1 r 1 1 1 1 1 ( ) ( ) [( ) ] r r r r r s r s s r s s r r s = 0 × + × = -× = i i i ⎧ ⎪ ⎨ ⎪ ⎩ $ $ 2 r 2 0 r s s = = i
According to the geometric feature of vector, it should be known that there is a common perpendicular among s 、 1 r 1 r r r and s ; and 2 r s s must be vertical each other,that is to say, the axis direction of the revolute joint must be located in the normal plane, which contained the twist, of the wrench.

When the joint is prismatic $ (0; )

s = $ $ 1 r 1 0 r s s = = i $ $ 2 r 0 = ⎧ ⎪ ⎨ ⎪ ⎩
According to the geometric feature of vector, it should be known that s and 1 r s must be vertical each other, that is to say, the moving direction of the prismatic joint and the axis direction of twist must be vertical each other.

When the structural conditions of limb meet with the above requirements, the limb should provide one twist and one wrench. According to the requirements above, we should put up the limb-RPRR shown as Fig. 7. Fig. 7. Structur of Limb RPRR-1F1M(s 2 ┴s r1 ,s 1 ┴s r2 , s 3 ┴s r2 ,s 4 ┴s r2, s 1 ,s 3 ,s 4 and s r2 are in the same plane)

The limb with two twists and one wrench

The basic expression of screw is

$ 1 r 1 1 1 ( ; ) r r r s r s = × $ 2 r 2 2 2
( ;

r r r s r s ) = × $ 3 r 3 (0; ) r s =
It is known from the reciprocal of screw that the limb should consist of the three independent screws which are reciprocal with the screws.

When the joint is revolute$ ( ;

) s r s = × $ $ 1 r 1 1 1 1 1 ( ) ( ) [( ) ] r r r r r s r s s r s s r r s = 0 × + × = -× = i i i $ $ 2 r 2 2 2 2 2 ( ) ( ) [( ) ] r r r r r s r s s r s s r r s = 0 × + × = -× = i i i $ $ 3 3 0 r s s = = i r ⎧ ⎪ ⎪ ⎨ ⎪ ⎪ ⎩ ⎧ ⎪ ⎪ ⎨ ⎪ ⎪ ⎩
According to the geometric feature of vector, it should be known that there is a common perpendicular among s 、 s must be vertical each other, that is to say, the axis direction of revolute joint, which must be vertical the axis direction of the wrench, must pass the point which is the point of intersection with the two twists or be parallel the plane which make sure by the two twists.

When the joint is prismatic $ (0; )

s = $ $ 1 r 1 0 r s s = = i $ $ 2 r 2 0 r s s = = i $ $ 3 r 0 =
According to the geometric feature of vector, it should be known that s and 1 r s must be vertical each other; s and 2 r s must be vertical each other; s is independent of 3 r s , that is to say, the axis moving direction of the prismatic joint,

⎧ ⎪ ⎪ ⎨ ⎪ ⎪ ⎩
which is independent of the axis direction of the wrench, must be parallel the crossproduce of the two twists.

When the structural conditions of limb meet with the above requirements, this limb should provide two twists and one wrench. According to the requirements above, we should put up the limb-RRP shown as Fig. 8. Fig. 8. Structur of Limb RRP-2F1M(s 1 ┴s r3 ,s 2 ┴s r3 ,s 3 ┴s r1 ,s 3 ┴s r2 , s 1 ┴s r1 ×s r2 , s 2 ┴s r1 ×s r2 )

The limb with one twist and two wrenches

The basic expression of screw is

$ 1 r 1 1 ( ; )
( ; ) s r s = × $ $ 1 r 1 1 1 1 1 ( ) ( ) [( ) ] r r r r r s r s s r s s r r s = 0 × + × = -× = i i i $ $ 2 2 0 r s s = = i r $ $ 3 r 3 0 r s s = = i
According to the geometric feature of vector, it should be known that there is a common perpendicular among s 、 s must be vertical each other, that is to say, the axis direction of revolute joint, which is in the same plane with the twist, must be parallel the crossproduce of the two wrenches.

When the joint is prismatic $ (0; )

s = $ $ 1 r 1 0 r s s = = i $ $ 2 r 0 = ⎧ ⎪ ⎪ ⎨ ⎪ ⎪ ⎩ ⎧ ⎪ ⎪ ⎨ ⎪ ⎪ ⎩ $ $ 3 r 0 =
According to the geometric feature of vector, it should be known that and 1 r s s must be vertical each other, that is to say, the axis moving direction of the prismatic joint must be vertical the axis direction of the twist.

When the structural conditions of limb meet with the above requirements, the limb should provide one twist and two wrenches. According to the requirements above, we should put up the limb-RRP shown as Fig. 9.

Example of the application

Since it is regular for the geometric conditions of the joint in the limb, which connects fixed platform with mobile platform, the limb, which meets with the geometric conditions, can be used to establish the parallel mechanism which be satisfied with the mode of motion. Now take the limb Fig. 7 as an example to establish the 3-2T1R parallel mechanism as shown in Fig. 10. The limb in Fig. 7 provides one twist along the Z-axis, which constrain the moving along the Z-axis, and one wrench along the Xaxis, which constrain the rotation around the X-axis. Thanks to the wrenches which provided by the three limbs are dependent in the XY plane, it should constrain the rotation around the X-axis and Y-axis, that is to say, the platform just can revolve around Z-axis and move in the XY plane.

Conclusions

According to analyze the type of limb and the type of restraint in screw theory, it is given a general design method of limb in the parallel mechanism. And that, it obtained the geometric conditions which the prismatic joint or revolute joint of overconstrained parallel mechanism must be meet with. The method analyzed from basic concept of the reciprocal produce in screw theory. It should make sure be general and pragmatic. It is a common reference value to the basic design of the parallel mechanism.

  the formula, stands for a unit vector along axis of twist and for a point on the axis direction of twist. Wrench should provide constraint for rotation in space. It can be defined as$

Fig. 1 .

 1 Fig. 1. Structur of Limb RRPRR-1F (s r //s 1 //s 2 ┴s 3 , s 4 ands 5 intersect at o, s r acting on o)

-

  and s ; a common perpendicular among s 、

  Fig 2.

Fig. 2 .

 2 Fig. 2. Structur of Limb RRPR-2F (s 1 ┴s r1 ×s r2 s 2 ┴s r1 ×s r2 , o is the point of action with s r1 and s r2 )

Fig. 3 . 2 . 4

 324 Fig. 3. Structur of Limb RRR-3F (s 1 , s 2 , and s 3 intersect at o)

Fig. 4 ..

 4 Fig. 4. Structur of Limb RRPRP-1M(s 1 //s 2 , s r //s 2 ×s 4 )

Fig. 6 ..

 6 Fig. 6. Structur of Limb PPP-3M (s 1 , s 2 and s 3 are independent each other)

  It is known from the reciprocal of screw that the limb should consist of the three independent screws which are reciprocal with the screws.When the joint is revolute $

Fig. 9 .

 9 Fig. 9. Structur of Limb RRP-1F2M (s 1 // s 2 //s r2 ×s r3 , s 3 ┴s r1 ,s 1 , s 2 and s r1 are in the same plane )

Fig. 10. 3 -

 3 Fig. 10. 3-2T1R parallel mechanism


Li Qiulian

Lei Zejian

Mingyin Yao
email: mingyin800@126.com

Jinlong Lin

Long Xue

Muhua Liu

Qiulian Li

Zejian Lei

Discrimination of Ca, Cu, Fe, and Na in Gannan Navel Orange by Laser Induced Breakdown Spectroscopy

Keywords: LIBS, Gannan Navel orange, Mineral elements, Discrimination

de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

There are plentiful nutrient elements in fruits. The intake of trace mineral elements from fruits is one of the most important pathways for the human body to absorb dietary minerals necessary for the healthy development. Detection and analysis of trace mineral elements in fruits, and more generally in food, can provide useful assessment and control for safe and healthy alimentation. However, detection and analysis of trace and ultra-trace elements in these substances need highly sensitive detection technique.

Usually, the conventional nutrient elements analysis methods, such as ICP-OES (Inductively Coupled Plasma Optical Emission Spectrometer),AFS (Atomic Fluorescence Spectrometry) ,AAS (Atomic Absorption Spectrometry) [START_REF] Yao | Determination of Thallium and Other Heavy Metals in Rice by ICP-MS and Assessment on Rice Safety by Thallium Contamination[END_REF][START_REF] Winefordner | Comparing several atomic spectrometric methods to the super stars: special emphasis on laser induced breakdown spectrometry,LIBS,a future super star[END_REF][START_REF] Iv | Determination of barium,chromium,cadmium,manganese,lead and zinc in atmospheric particulate matter by inductively coupled plasma atomic emission spectrometry(ICP-AES)[END_REF] ,are comprised by the following steps: taking a sample from the substance or from a processing product line to be inspected; transporting it to an inspection device or to a laboratory; preparing it for chemical analysis; and for determination. The sample preparation for chemical analysis is a required stage for many analytical techniques, which consists in transforming the sample into an appropriate form for the analysis. For the elemental analysis, the solid samples are usually changed to solutions, which carry the analytes free of organic matter. This step is usually the most time consuming analytical procedure, in addition to generating toxic residues and increasing the probability of sample contamination.

Laser Induced Breakdown Spectroscopy(LIBS)is an emission spectroscopy technique that makes use of a high energy laser pulse to simultaneously prepare the sample and excite the species. LIBS is employed to determine the elemental composition of a sample, regardless of whether the sample is a solid, liquid or gas, with no or little sample pretreatment procedures. Due to its instrumental features, LIBS is a promising technique for in situ analysis, including direct analysis at the processing line. During solid sample analysis, its surface is irradiated by a high energy laser pulse, immediately giving rise to material ablation. The sample ablated generates a high temperature plasma plume. As a result of the temperature, the ablated material breaks down into excited ionic and atomic species. The excited species usually return to their fundamental states, emitting characteristic radiation, consequently the qualitative analysis of the emission spectrum provides the sample's ''fingerprint" regarding its elemental composition [START_REF] Cremers | Handbook of Laser-Induced Breakdown Spectroscopy[END_REF][START_REF] Jagdish | Laser-Induced Breakdown Spectroscopy[END_REF] .

However, performing a quantitative analysis is no simple matter, as the element emission lines in the LIBS spectrum are closely related with the matrix in which they are embedded. The matrix effects occur in the LIBS spectra for several reasons, however the major cause of them is the change of temperature and electron density of the plasma induced on different matrix targets. This is due to variations in both the ablation and laser plasma interaction processes, resulting also in possible variations of plume expansion in the background gas. As a result, different excitation and ionization levels of plasma species are achieved. This signal feature makes it difficult to find the appropriate calibration standards for the LIBS methods. In some cases the appearance of the so-called matrix effects can be reduced by using a multivariate calibration, internal standard or calibration free method [START_REF] Tawfik | Calibration free laser-induced breakdown spectroscopy (LIBS) identification of seawater salinity[END_REF][START_REF] Sirven | Qualitative and quantitative investigation of chromiumpolluted soils by laser-induced breakdown spectroscopy combined with neural networks analysis[END_REF] , however significant efforts have been made to adapt conventional calibration to LIBS methods. Vincent Juvé [START_REF] Cristina Trevizan | Evaluation of laser induced breakdown spectroscopy for the determination of macronutrients in plant materials[END_REF] analyzed fresh vegetables using ultraviolet nanosecond LIBS. Lilian Cristina Trevizan [START_REF] Cristina Trevizan | Evaluation of laser induced breakdown spectroscopy for the determination of micronutrients in plant materials[END_REF][START_REF] Juvé | Space-resolved analysis of trace elements in fresh vegetables using ultraviolet nanosecond laser-induced breakdown spectroscopy[END_REF] evaluated the macronutrients and micronutrients in plant materials by a Q-switched Nd:YAG laser. Edilene C.Ferreira [START_REF] Edilene | Determination of Ca in breakfast cereals by laser induced breakdown spectroscopy[END_REF] detected Ca in breakfast cereals by LIBS.

In this paper, a new proposal for Ca, Cu, Fe, and Na semi-quantitative and qualitative determination in the pericarps and fleshes of Gannan Navel orange using LIBS was evaluated. The method will provide easy sample preparation and fast measurement for agricultural food products, botanical materials and material of similar matrix.

Materials and Methods

LIBS Experimental Setup

The experimental setup sees Figure 1.A Q-switched Nd:YAG laser (BeamTech, Nimma-200,China) operating at the fundamental wavelength(1064 nm) was employed. Laser pulses with (200±2) mJ, 8 ns pulse width at 10 Hz repetition rate were generated with a 6 mm beam diameter. The laser pulse was focused on the sample pellet by a convergent lens with 30 mm diameter and 200mm focal length (China Optical Coating Laboratory, Inc). The 35 mm diameter pellet was placed into a plastic sample holder in single axes automatic controlled rotation stage that moved in the plane orthogonal to the laser direction.

The plasma emission was colleted by the spectrometer fiber (1.5 m length, 400 um core diameter) matching its numerical aperture. The optical axis of the collecting system was approximately 45° from the laser axis. A eight-channel model AVS-Rackmount-USB2 spectrometer (Avantes, France) equipped with echelle optics was used, which provides the wavelength range between 200 and 1100 nm with a resolution of 0.09 nm at 200 to 317nm, 0.07 nm at 315 to 417nm, 0.06nm at 415-499nm, 0.08nm at 497-565nm, 0.08nm at 563-673nm, 0.12nm at 671-750nm, 0.13nm at 748-931nm, and 0.11nm at 929-1050nm.The detector is a 2048 pixel ICCD camera. The dark current of the ICCD was automatically subtracted from the measured spectral data. The integration time and the delay time were fixed at 2ms and 1.28 us respectively for all measurements presented in this work.

Samples and Materials

Twenty fresh Gannan Navel oranges were chosen to perform preliminary experiments. The fruits were washed separately with running tap water and further rinsed twice with distilled water. After washing and natural air drying, the fruits were divided into pericarps and fleshes samples. The samples were chopped and placed in sample chamber with diameter 35mm.Ten spectra of each sample were collected from different positions. In order to take in account the fluctuations of the laser, the average of 10 spectra in each sample was considered as a single measurement. The plasma was induced on the surface of the pericarps and fleshes in fresh Gannan Navel orange. To represent the relative concentrations of the analyzed elements, the intensity of Cu at 939.0176nm, Ca at 926.5298nm, Fe at 656.2375nm and Na at 588.995nm were considered for the proposed LIBS method. These lines are chosen for their high intensities and low fluctuations from a spectrum to another. Typical spectra of pericarps and fleshes are shown in Figure 2 and Figure 3.Table 1 provides detailed information of Cu 939.0176nm, Ca 926.5298nm, Fe 656.2375nm and Na 588.995nm in the spectrum of fresh Gannan Navel orange.

From Figure 2, Figure 3 and Table 1, the relative intensity of Ca,Cu,Fe and Na was higher in pericarps than in fleshes. As for same or similar matrix, the relative intensity of elements LIBS is proportional to their concentration, so, the accumulation of Ca,Cu,Fe and Na was obvious in pericarps than in fleshes .Moreover, the relative intensity of elements Cu and Ca was twice in pericarps than in fleshes, and the intensity of Na was far higher in pericarps than in fleshes. The observation and statistics showed that the difference of concentration of mineral elements in pericarps and fleshes.

Conclusions

In this work, mineral elements detection, qualitative analysis and semiquantitative analysis have been demonstrated in fresh Gannan Navel orange using LIBS technique. However, works are still needed to be accomplished in order to understand in detail the plasma generation in a complex matrix such as pericarps and fleshes tissue. Such a detailed understanding would allow a quantitative analysis of trace elements in fruits. The results obtained in this work show the potential of the LIBS technique to provide an interesting tool for detection and analysis of trace elements in fresh fruits and more generally in food. Trace element detection and analysis in fruits represent important issues for the assessment and the control of food quality and safety, as well as for the detection and the monitoring of the environment pollutions including heavy metal charges in soil, water and air.

Fig. 1 .

 1 Fig. 1. LIBS experimental setup

Fig. 2 .Fig. 3 .

 23 Fig. 2. Typical LIBS spectra of Ca、Cu、Fe、Na in pericarps

Acknowledgments. The authors are thankful to key laboratory of modern agricultural equipment and technology (Ministry of Education & Jiangsu province, Jiangsu University), Program for New Century Excellent Talents in University and National Natural Science Foundation of China (No.30972052) for financial support.


Shangmin Deng

Weili Men

Evaluation Evaluation Evaluation Evaluation on on on on the the the the Agricultural Agricultural Agricultural Agricultural Website's Website's Website's Website's Efficiency Efficiency Efficiency Efficiency Based Based Based Based on on on on DEA DEA DEA DEA Method Method Method Method

Keywords: Agricultural information website, Efficiency of website, Data Envelopment Analysis (DEA), Evaluation research

An information-driven agriculture is firstly agriculture digitalization, the foundation of which is the construction of agricultural information networks. Based on the methods of website evaluation, an indicator system of efficiency evaluation for agricultural information websites is constructed in this thesis. Then the efficiency of 17 municipal websites in Shandong province are analyzed by the C2R Model in DEA. The result declares that 3 of these websites are related effective and the other 14 are non-effective. By an analysis of projection, this thesis also gives suggestions to improve the performance of the non-effective

Introduction Introduction Introduction Introduction

Issues concerning agriculture, countryside and farmers, are called Three Rural Questions, which take an crucial part in the realization of the goal of a well-todo society and the development of our country's economy. It is acknowledged that it will be harder for uninformed districts to develop their own agriculture. Nowadays, the information gap between urban and rural areas has attracted wide attention of experts from Information Science. The Party Central Committee, since 16th party congress ,hammers away at the point that we should always take addressing the problems facing China's agriculture as the top priority of our economic, and also put forward "to boost the county economy" at the same time. One of "the Three Most Requirement", raised on the Third Plenary Session of the 11th Central Committee of the C.P.C, is that the position of agriculture as the foundation is still weak and need to brush up on the most. In March 2010,the government of Shandong province makes the implementation of the plan named "Powerful Province of information" and the development of Digital Agriculture positively as key points to promote new Information Industries. [START_REF] Liu | Study on the Indicator System for Measuring the Rural Area Informatization Level in China[END_REF] The informationization of agriculture, in the first place, is digitalization, which means to devote major efforts to develop the digital agriculture. As we all know that ,the foundation of digitalization is the construction of information networks and the service level is determined by such factors as the resources ,the infrastructural facilities and the environment of informationization ,as well as the human resources and the effectiveness of agricultural information services .In another word ,the informationization of agricultural service can be demonstrated by that of agriculture. [START_REF] Han | Evaluation and Study on Development of Agriculture Information Service[END_REF] So, it is reasonable to estimate the present situation of agriculture services .However, because of the difference in geographical conditions and culture backgrounds, we need a appropriate method to selected samples comprehensively and objectively. Fortunately there is a successful precedent created by the DEA (Data Envelopment Analysis for short) which is convenient and practical. [START_REF] Hu | Evaluation on agriculture sites in western area Based on DEA and Cluster analysis[END_REF]

Data Data Data Data Envelopment Envelopment Envelopment Envelopment Analysis Analysis Analysis Analysis

DEA which is short for Data Envelopment Analysis is a new system analytic method.It was firstly put forward by two operational research experts, A.Charnes and W.W.Copper, to deal with inputs and outputs subject to random disturbances ,according to the relative efficiency and evaluation of returns for familiar departments. Based on the concept of relative efficiencies, this method evaluates the relative efficiency of DMUs (Decision Making Units for short) by linear programming model. Besides evaluate and list DMUs as relative efficiency, the results also will point out existing problems and improvement for non-efficient DMUs. Furthermore, instead of setting the weight of inputs/outputs beforehand, DEA gets objective value for each random variable by computing actual datas,which makes the conclusion independently and impartially. [START_REF] Du | contemporary Comprehensive evaluation methods and classic documentation[END_REF] In the light of different research purposes, there are many different DEA models. In this thesis, we select the C2R model just because we want to study whether the DMUs are technique and scale simultaneously efficient when to decrease its inputs by suitable times with its unchanged outputs. The DMU is technique or scale efficient unless it is DEA efficient; otherwise, it will be not efficient.

D D D Description escription escription escription of of of of the the the the M M M Model odel odel odel of of of of C C C C 2 2 2 2 R R R R

As the first evaluation model, the results of C 2 R can be used to demonstrate the efficient of DMUs. For the sake of our discussion we assume that the number of DMUs is n, and the number of input and output variables each DUM has is "m" and "s" respectively. we also set up a mathematical formula of the relationship for the two kinds of variables to fulfill: Xj=(X1j,X2j,X3j,…,Xmj)T≥0, Yj=(Y1j,Y2j,Y3j,…,Ysj)T≥0, j=1,…,n;

At the same time ,other certain conditions should be satisfied: Xij>0, Yrj>0,i=1,2,…,m;r=1,2,…,s.

The model is known as efficiency evaluation of decision-making units such as j0, subject to meeting the efficiency of all the DUMs at checkpoints, then we come to a C 2 R modle with non archimedean infinitesimal vector. The optimality is relative efficiency of a DMU, as contrasted with other DUMs , according to what have we suggested. [START_REF] Lan | The Evaluation of China s Circulation Economy Efficiency Based on DEA[END_REF] Here, we useθas the input proportional variable,ε as the non archimedean infinitesimal vector (usually, we let it be 10-6 );

=(1,1…, 1)∈Em, =(1,1…,1)∈Es; =( … ) is slack variables correspond to inputs, = ( … )
is the variable to output and the λj is the decision variable for the appointed DMU.

When this model is applied to data, we will get the optimal solution composed of λj ,S*-, S*+ and θ*.There are several results that we should make into our consideration:

(1)When θ0=1,s0-=0 and s0+=0, we think the DMU is efficiency which means technique and scale are simultaneously efficient.

(2) When θ0=1, -,but s0-≠0 or s0+≠0, we believe that under some conditions the DMU is weak DEA efficient. In other words, the either technique or scale is efficient.

(3) When θ0<1,the performance of this DUM is of non-effective. Therefore, we consider it as Effective Decision-making Units when θ0=1;otherwise,it is ineffective. [START_REF] Wu | evaluation on the efficiency of eco-technology Innovation based on DEA[END_REF]

Efficiency Efficiency Efficiency Efficiency evaluation evaluation evaluation evaluation on on on on agriculture agriculture agriculture agriculture websites websites websites websites

Now, the number of municipal cities in Shandong province is about 91,which counts for 65%. Intra-county economy plays a vital role in the development in the informationalization of our province. Even though, much attention has been paid on the informationization of agriculture, there are still many problems that should take into our focus. Researches on agriculture websites will not only improve the design and maintenance for websites of corporations, but also promote the standardization of the management and speed up the process of agricultural modernization in Shandong Province. [START_REF] Tan | Study on the Evaluation of Agriculture Web Site[END_REF] 4.1 4.1 4.1 4.1 Evaluating Evaluating Evaluating Evaluating Index Index Index Index

The purpose of this thesis is to evaluate the agriculture websites in Shandong province. The main method is to study the inputs effectiveness while keep outputs steady. To make the result objective and easy to analyze, we choose such inputs (inps for short) variables as TAG (Total number of web pages), APS (Average page size), TFS (Total foreign sites that link to this site), UDR (Updata rating), NBL (No broken links), FRP (Foreign (external) pages referenced),NRP (Non returning percentage ) and CP (Connected percentage). [START_REF] Sun | Evaluation on the Western Agricultural Website s Efficiency Based on DEA Method[END_REF] TAG is the number of static and dynamic pages belonging to the same root directory. APS describes the average pages size classified by 10k times.TFS evaluates the networks, inputs variables effectiveness from the perspective of website promotion. UDR is a relative concept. Maintainers usually update different content types in different times. So before we estimate the upiea objectively, we need to classified different updating periods in sorts. In this thesis, we divide the periods into four catalogues. According to the different influence, we give weights to the periods respectively. NBL means using this kind of links , we can not find the target website. Though this, we have another way to measure the effective of websites. The more FRP is, the longer time it will take to operate the website. NRP have the similar function as CP. Both of them evaluate the effectiveness of website from the eye of site navigations Output (outp for short) variables we choose means the number of visitors to the site ,which has a certain relation with TFS. Because a visitor may glance over many different documents or more than one websites, the clicks may be much larger. [START_REF] Qiu | Theory Research and Application for DEA in websites evaluation[END_REF]

Sample Sample Sample Sample

To determine the Agricultural Website's Efficiency,we choose 17 sites as DMUs set, built by Agricultural Information Centre of Shandong province and subordinate departments. They have common in many aspects such as contents, receivers and functions, which meet the requirements for application of C 2 R model in DEA.

Data Data Data Data

Using Maxamine [START_REF]Web Analyst Software Package[END_REF],a specialized profiler to make a analysis of networks, the mentioned sites were scanned. The objective datas we collected includes the internal information of the sites and interconnection information between networks, among which, the UDR are calculated as table 1 .

The output consult verified test results from alexa.com, an authoritative Third-party certification website, applying the number of visitor for the targeted site. Table Table 1 1 Form table 2, we can see that three DUMS are of effective units in DEA. In other words, the others 14 are non DEA efficient, among which, there are four websites have an effectiveness below 0.01. Therefore, it can be concluded that, the agricultural sites, efficiency in Shandong are lower than expected.Then, we make an projection analysis for the non DEA efficient based on the DEAP2.1 results. The main task is to analyze relative improvement of inputs when outputs is remain unchanged. We also calculate potential improvements of inputs and outputs under ideal condition. The average potential improvements are showed in table 3.The potential improvements demonstrate that, reference to the non DEA efficient DMUs, we have not make full use of each input already, so, in theory at least, we can promote the sites efficiency and induce inputs. If we keep inputs still, the output is also can be promoted by 61%. In other words, if inputs can not be reduced, theoretical, efficiency can be raised by the increasing number of visitors Table 4 shows main factors influencing websites efficiency, including FRP, TAG, NRP and APS.

Table Table

Reduce Reduce Reduce Reduce TFS TFS TFS TFS. . . . This method includes reducing inputs of website promotion or increase the number of the visitors. On some degree, TFS represents the stability of a website, yet the more external links are , the higher it will cost. Checking dead links, updating old links and other resources maintenance will affect the operation efficiency. So, in order to promote the efficiency, we need to reduce TFS while the quality of the web is ensured. Only in this way, can we attract more attention and keep the site authority.

Conclusions Conclusions Conclusions Conclusions

Though all the above mentioned, we have a clear idea that there are 14 websites are non DEA efficient , which counts for 84.3% of all municipal websites in Shandong province. We have presented a detailed accounting of efficiency of agricultural websites and suggestions are also given to improve the current situation. Evaluation of the agriculture websites' efficiency can not only reflect the present situation of Shandong agriculture, but also be valuable for further development in the construction of information agriculture and application of related net resources.

Table able able able 2: 2: 2: 2:

  1 1:Calculation methods of update rate of website Appraisal index of the efficiency of websites in shandong province

	update cycle of pages	update rate Ri	Weight λ	update rate of website
	≤ 1 week	R1	0.50
	1 week ~6 weeks	R2	0.30
	6 weeks ~6 months	R3	0.15
	≥6 months	R4	0.05
	T T T name of	the efficiency	name of	the efficiency
	counties	of website	counties	of website
	Qingdao	1.000	Dongying	0.284
	Weihai	1.000	Weifang	0.243
	Jinan	1.000	Binzhou	0.143
	Zibo	0.662	Linyi	0.122
	Liaocheng	0.494	Dezhou	0.057
	Laiwu	0.439	Tai-an	0.055
	Jining	0.395	Zaozhuang	0.050
	Yantai	0.362	Rizhao	0.042
	Heze	0.315

From table 2, we know that the operation efficiencies are very different among these 17 municipal agriculture websites, even though most of them are inefficient. Reference to non DEA efficient, combined with the analysis of table 3 andtable 4,we suggest that the relative departments should take such actions as following to improve the performance of the non DEA efficient:


Qin Song
email: song_qin@yeah.net

Fukuan Zhao
email: zhaofukuan@sina.com

Yujun Zheng
email: zhengyujun@yahoo.cn

A Tabu Sear ch Appr oach to Fuzzy Optimization of Camellia Oleifera Fer tilization

Keywords: fuzzy optimization, tabu search, Camellia oleifera

Abstr act. Traditional optimization methods have been applied for years to high-yield fertilization models, which are usually well formulated by crisp coefficients and variables. Unfortunately, real-world crop growing environment and process are often not deterministic. In this paper we establish a fuzzy mathematical model between Camellia oleifera yield and fertilization application rates, in which variation coefficients of N, P, K are described with fuzzy numbers. In particular, we present a tabu search algorithm for finding a set of fertilization solutions in order to maximize Camellia oleifera yield based on fuzzy measures including expected value, optimistic value and pessimistic value. Our approach is more realistic and practical for real-world problems by taking vague and imprecise data into consideration, provides more comprehensive decision support by generating a set of high-quality alternatives, and can be applied to fertilizer decision for a variety of other crops.

Intr oduction

Crop yield response models have been playing an increasingly important role in variable-rate fertilization decision-making. There are several widely-used quantitative mathematical models including the linear-plus-plateau model, the quadratic-plus plateau model, the quadratic model, the exponential model, and the square root model, which often disagree when identifying the fertilizer application rates [START_REF] Cerrato | Comparison of models for describing corn yield response to nitrogen fertilizer[END_REF]. In many cases, it is hard for the farmers to place a high confidence level on the results of the models, the main reason of which is that the models always generate so exact and crisp solutions but the environment is uncertain and the measurement is imprecise in nature. For example, rather than say that "the crop yield would be 1000kg", it is more reasonable to say that "the crop yield would be at least 800kg, at most 1150kg, and most likely to be 1000kg".

First initialized by Zadeh [START_REF] Zadeh | Fuzzy sets[END_REF], the concept of fuzzy sets has been well developed and applied to many conventional mathematical methods to reflect the ambiguity and uncertainty in real world. However, until recent years, little attention has been given to fuzzy mathematic models on crop growth and yield. Kandala and Prajneshu [START_REF] Kandala | Fuzzy regression methodology for crop yield forecasting using remotely sensed data[END_REF] first proposed a fuzzy linear regression approach for crop yield forecasting using remotely sensed data which lies in an interval instead of a single number. In [START_REF] Yu | Fuzzy evaluation of different irrigation and fertilization on growth of greenhouse tomato[END_REF] Yu et al selected linear functions as membership functions in fuzzy synthesis evaluation of different irrigation and fertilization on growth of greenhouse tomato. Fuzzy decision concepts have also been used on the extension of some other optimization methods in agriculture fertilizer applications. For example, Li et al [START_REF] Li | A new approach for fuzzy fertilization forecast based on support vector learning mechanism[END_REF] presented a support vector machine algorithm to generate fertilization fuzzy rules to increase linguistic interpretability and acquisition capability of knowledge. Palaniswami et al [START_REF] Palaniswami | A fuzzy neural network for coconut yield prediction[END_REF] used a fuzzy neural network to predict the coconut yield in which fuzzy membership values of the independent variables were used as the input layer for the network.

In this paper we establish a fuzzy mathematical model between Camellia oleifera yield and fertilization application rates, in which variation coefficients of N, P, K are described with fuzzy numbers. Under the fuzzy environment, it is not desirable to find a single optimum for Camellia oleifera yield by applying one-step optimization techniques such as the Gauss-Newton method, and thus we present an extended tabu search algorithm for finding a set of Pareto optimal solutions based on fuzzy measures including expected value, optimistic value and pessimistic value. In comparison with crisp methods, our approach is more realistic and provides more comprehensive decision-making support by taking uncertain information and multiple criteria into consideration.

Pr eliminar ies

First we present some basic concepts of fuzzy sets, sufficient to understand the paper.

A fuzzy set is a pair (A,μ) where A is an ordinary set and μ is a function: A[0,1]. For each x ∈A, μ(x) is called the grade of membership of x in (A,μ). x is said to be not included in (A,μ) if μ(x)=0, x is said to be fully included if μ(x)=1, and x is called a fuzzy member if 0<μ(x)<1. Let X be the universe of discourse, A fuzzy set Ã=(A,μ) of X is said to be convex if and only if for all x 1 and x 2 in X and λ∈[0,1] the following equation always holds:

μ(λx 1 +(1-λ)x 2 ) ≥ min(μ(x 1 ), μ(x 2 )) (1)
A fuzzy number is a convex, normalized fuzzy set (A,μ) whose membership function is at least segmentally continuous and has the functional value μ(x) = 1 at precisely one element, where A is a subset of the real number R.

One of the most commonly used fuzzy numbers is the triangular fuzzy number represented by (a,b,c), whose membership function is defined as follows: c 2 ) be two triangular fuzzy numbers, the basic fuzzy arithmetic operations on them are defined as follows [START_REF] Dubois | Operations on fuzzy numbers[END_REF][START_REF] Kaufmann | Introduction to Fuzzy Arithmetic Theory and Applications[END_REF]:

     < ≤ - - < ≤ - - = otherwise , 0 if ), /( ) ( if ), /( ) ( ) ( c x b b c x c b x a a b a x x µ (2) Let  à 1 =(a 1 ,b 1 ,c 1 ) and à 2 =(a 2 ,b 2 ,
à 1 +à 2 = (a 1 +a 2 ,b 1 +b 2 ,c 1 +c 2 ) (3) à 1 -à 2 = (a 1 -c 2 ,b 1 -b 2 ,c 1 -a 2 ) (4) λà 1 = (λa 1 ,λb 1 ,λc 1 ) (5) à 1 ×à 2 = (a 1 a 2 ,b 1 b 2 ,c 1 c 2 ) (6) à 1 /à 2 = (a 1 /c 2 ,b 1 /b 2 ,c 1 /a 2 ) (7)
For fuzzy numbers, there is a variety of measures developed ranging from the trivial to the complex. Liu [START_REF] Liu | Uncertainty Theory[END_REF] proposed a credibility measure that satisfies normality, monotonicity, self-duality, and maximality. Given a  triangular fuzzy number Ã=(a,b,c) and a credibility level λ∈[0,1], the expected value, α-optimistic value and αpessimistic value of à are respectively defined as follows:

E(Ã) = (a+2b+c)/4 (8)    - + - ≤ - + = else , ) 2 2 ( ) 1 2 ( 5 . 0 if , ) 2 1 ( 2 ) ( b a c b x O λ λ λ λ λ λ (9)    - + - ≤ + - = else , ) 1 2 ( ) 2 2 ( 5 . 0 if , 2 ) 2 1 ( ) ( c b b a x P λ λ λ λ λ λ (10)

A Fuzzy Fer tilizer Response Model for Camellia Oleifera

A field experiment was conducted in Yichun area, Jiangxi province, China. The selected Camellia oleifera trees were in full bearing period. The experimental area was 360 ha and divided into 45 parts, and the plant density is about 68~75 trees/ha. The three-factor quadratic model was used for describing the relationship between the yield of the fruits (kg/ha) and the concentration of N, P, and K: Nevertheless, we should be careful here for negative coefficients: the addition of two negative fuzzy numbers should use the Equation (3), while the addition of a positive fuzzy number and a negative fuzzy number should use the Equation ( 4); if a fuzzy number contains both positive and negative components, e.g., ã 1 = (-0.5, 0.5, 1.0), we should perform a normalization on the equation to make it contain only pure positive numbers and pure negative numbers.

d K c P c N c NK b PK b NP b K a P a N a Y 3 2 1 3

A Tabu Sear ch Algor ithm for Finding Optimal Fer tilization Solutions

Since fuzzy numbers are represented in nature by possibility distributions, it is difficult to determine clearly whether one fuzzy number is larger or smaller than the other [START_REF] Kwang | A method for ranking fuzzy numbers and its application to decision-making[END_REF]. In consequence, for quadratic regression models with fuzzy coefficients, it is not desirable to find a single optimum for by applying one-step optimization techniques such as the Gauss-Newton method. Instead, we should use a comprehensive approach that takes more than one ranking criteria into consideration.

To measure and compare the results of the fuzzy yield response model [START_REF] Kwang | A method for ranking fuzzy numbers and its application to decision-making[END_REF], we employed here three important fuzzy ranking criteria including expected value, optimistic value and pessimistic value. Given two fertilizer solutions which result in yields 1 Ỹ and 2 Ỹ respectively, we say

1 Ỹ dominates 2 Ỹ if they satisfies ) ( ) ( 2 1 Y E Y E ≥ , ) ( ) ( 2 1 Y O Y O ≥ and ) ( ) ( 2 1 Y P Y P ≥
. Under the circumstance of multiple criteria decision, it is desired to find a set of non-dominated solutions instead of a single one.

Tabu search, first proposed by Glover [START_REF] Glover | Tabu search, part I[END_REF][START_REF] Glover | Tabu search, part II[END_REF], is a meta-heuristic search that repeatedly moves from a current solution to the best of neighboring solutions while avoiding being trapped in local optima by keeping a tabu list of forbidden moves. It was extended to continuous problems by Cvijovic and Klinowski [START_REF] Cvijovic | Taboo search: an approach to the multiple minima problem[END_REF] and to multi-objective optimization problems by Hansen [START_REF] Hansen | Tabu search for multiobjective optimization: MOTS[END_REF]. The follows present an innovative tabu search algorithm for working out the non-dominated fertilizer solutions for the Camellia oleifera yield response model:

Step 1. Find an arbitrary initial solution x 0 , initializes the empty tabu list T, let x = x 0 , E * = E(x 0 ), O * = O(x 0 ), P * = P(x 0 ), Q = {x 0 }.

Step 2. In the current solution's neighborhood N(x), select all the solution x' that satisfies any of the following criteria: (1) E(x') > E * , (2) O(x') > O * , (3) P(x') > P * , add x' to the solution set Q and delete those solutions being dominated by x' from Q, and update E * , O * , or P * . If E(x') E * , update the tabu list T and let x = x', go Step 2.

Step 3. If no such a solution satisfying E(x') > E * and all the neighborhood solutions are tabu, or some of the termination conditions are reached, the algorithm stops and returns Q.

Step 4. Otherwise, select an x' in N(x)\T with the best expected value in E(x'), update the tabu list T and let x = x', go Step 2.

In the above algorithmic framework, the neighborhood of a fertilizer solution [x 1 , x 2 , x 3 ] is defined as the set of six solutions including [x 1 ±0.1, x 2 , x 3 ], 1 , x 2 ±0.1, x 3 ] and [x 1 , x 2 , x 3 ±0.1], where 0.1 is a preset increment value (for other yield response models, the increment value can be adjusted according to the units of measurement used and the fertilizer application quantities estimated).

We run the tabu search algorithm for solving the Camellia oleifera yield response model. The credibility level λ was set to 0.25; the algorithm stopped after 528 iterations, and the result non-dominated solution set contained 6 solutions as shown in Table 2. As we can see, solution #5 and #6 reached the maximum expected yield value 1162.5, in which #6 reached the maximum optimistic value 1295, and #1 reached the maximum pessimistic value 1036.

Conclusion

The paper establishes a fuzzy mathematical model between Camellia oleifera yield and fertilization application rates, in which variation coefficients of N, P, K are described with fuzzy numbers. In particular, we present a tabu search algorithm for finding the non-dominated fertilization solution set on three fuzzy measures including expected value, optimistic value and pessimistic value of the Camellia oleifera yield.

Our approach is more realistic and practical by taking vague and imprecise data into consideration, and supports more comprehensive decision-making by generating a set of high-quality alternatives.

The fuzzy yield response model can be applied to a wide variety of crops more reasonably and effectively, and the algorithmic framework can be applied/extended for solving the quadratic and other kinds of models. Moreover, more fuzzy ranking criteria can be included in order to providing more comprehensive and complicated decision support. Our ongoing work also includes developing an integrated software tool to support fuzzy data analysis, regression modeling, problem solving, and visualized fertilizer decision-making.

  Based on the historical data, the value ranges are set as 6.5 ≤ N ≤ 8.4, 11.5 ≤ P ≤ 15.8, 25.0 ≤ K ≤ 40.2. By performing fuzzy regression analysis based on the quadratic programming formulation[START_REF] Lee | Fuzzy approximations with non-symmetric fuzzy parameters in fuzzy regression analysis[END_REF], we obtained the regression coefficients in Equation (11) as shown in Table1.

	=	1	2	+	2	2	+	3	2	+	1	+	2		+	+		+	+	+	(21)
	where coefficients 1 ã , 2 ã , 3 ã , 1 b , 2 b , 3 b , 1 c , 2 c , 3 c and constant d ~ are
	all triangular fuzzy numbers. Table 1. The fuzzy regression coefficients
						1 ã		ã	2		ã	3	1 b	b	2	3 b	1 c	c	2	c	3	d ~
				a -0.66 -4.55 -0.39 6.45 1.84 -3.27 9.17 6.05 14.67 832.1
				b -0.60 -4.10 -0.35 6.70 2.00 -3.10 9.30 6.10 14.90 850.2
				c -0.52 -3.96 -0.32 7.20 2.25 -2.93 9.65 6.52 15.40 874.5

Table 2 .

 2 Non-dominated solution set for the Camellia oleifera yield response model

		N	P	K	Y	E(Y)	O(Y)	P(Y)
	#1	6.6	11.7	25.0	(931, 1140, 1365)	1144	1252	1036
	#2	6.8	11.8	25.0	(929, 1141, 1369)	1145	1255	1035
	#3	7.1	12.1	25.0	(924, 1143, 1380)	1147.5	1262	1034
	#4	7.3	12.3	25.0	(921, 1145, 1386)	1149.25	1266	1033
	#5	8.4	13.4	25.0	(905, 1158, 1429)	1162.5	1294	1032
	#6	8.4	13.6	25.0	(902, 1158, 1432)	1162.5	1295	1030

Acknowledgments. The work was supported by the Funding Project for Academic Human Resources Development in Institutions of Higher Learning under the Jurisdiction of Beijing Municipality (PHR200907136).


Lin Peng

Linnan Yang

Limin Zhang

I I I

Keywords: WebGIS, Agricultural environment, Information service system, Spatial database 1 1 1 1

Faced to the present agro-environmental information features, there exist several difficulties to acquire and control the agricultural environment information, such as the scattered information with spatio-tempel traits, the methods of quantification and the huge data amount. This paper constructed an agroenvironmental information service system based on the spatial database, computer network and geographic information system (GIS) technology. This system was applied in Jianshui County, Yunnan to implement the system functions including the collection, storage, analysis, visual output and intelligent evaluation. The system with these functions applied technical support for Jianshui county to improve the abilities both in local agricultural products and environmental protection. And it provided a precedent for other Counties in Yunnan to construct agricultural environmental information system.

soil and so on. And profile the corresponding digital map of these spatial data at the same time.

Third, a multi-index evaluation model was developed based on the above attribute database and spatial database to analyze the contamination degree of the air, water, soil and the soil fertility level. The evaluation model was integrated into WebGIS Components and could be used by consumers. The technique flow diagram of the system development was illustrated in Fig. 1. The agro-environmental information service system is built on the network technical architecture, so this paper integrated the network and GIS technology to develop and implement a practical agro-environmental information service system in Jianshui, Yunnan. SuperMap IS.NET was chosen to be the development platform in the new information service system, because the function and structure of SuperMap IS.NET WebGIS platform could satisfy the system development requirements which should be completed with compatibility, expansion, generalized data exchange format. And SuperMap Deskpro5 was chosen to be the plotting software to draw electronic map to improve the equipment compatibility because both of the SuperMap IS.NET and SuperMap Deskpro5 are the products from the same software company. At the same time, since the system would face the challenge of mass data storages and operations, SQL Server 2005 was used as system database development tool to solve the expansion and integration difficulties of the system database. Architecture Architecture Architecture Architecture. . . . B/S/D (Browser/Service/Database) three-layer architecture was used to implement the design and development of the system expandable, make the system module components reusable, and make the system services independent. (1) Database Layer SQL server database software was used as supporting software in database layer. All the designs included five spatial databases. They were spatial database of production resources information, spatial database of soil fertility information, spatial database of soil pollution information, spatial database of irrigation water information and spatial database of climate information spatial database.

(2) Service Layer SuperMap IS 2008 was used in Service layer to support the map generation and management functions.

(3) Browser Layer IE6.0 or above version was adopted to be the browser to develop the website. Web controls were used to invoke both of the services in the Service Layer and the User Interface. Browser layer has the functions of browsing map, editing map, spatial Analysis, query statistics, etc.

Network Network Network

The The The The Data Data Data Data Arrangement Arrangement Arrangement Arrangement

Data Data Data Data analysis analysis analysis analysis. . . . There were two types of data in this system, vector data and raster data.

The data design and the analysis were showed in Fig. 4. With the assistance of Jianshui Agricultural Bureau, chose 10 villages in 3 towns, they are Lin'an, Miandian and Puxiong in Jianshui, to be the investigation sites. Then, the agro-environmental information, which included atmosphere data, irrigation water data and soil data in these 10 villages were collected according to national environmental requirements on agricultural products base. Among these national standard, this system adopted GB5084-92 national standard on farm irrigation water, GB 3095-1996 national standard on atmosphere, and GB15618-1995 national standard on soil.

The collected data mainly includes geospatial information data and attribute data.

(1) Geospatial information data The geospatial information data is stored in 'eoo' format based on the administrative region map in Jianshui at 1: 50000.

(2) Attribute data The attribute data included main environmental information from 2005 to 2009, such as air data, irrigation water data, soil data, planted area data and other basic data. These data were provided by the Jianshui Agricultural Bureau from Status Survey on Agroenvironmental in JianShui.

The soil database sample was showed in table 1.

Table Table Table Table 1 1 1 1

. . . . Air pollution Index data

The irrigation water database sample was showed in table 2. Table Table 2 2 2 2

Table Table

. . . . Water pollution Index data

The soil heavy metal database sample is showed in table 3.

Table Table Table Table 3 3 3 3

. . . . Soil pollution Index data

Identifier Identifier Identifier Identifier Village Village Village Village Single Single Single Single pollution pollution pollution pollution index index index index comprehensive comprehensive comprehensive comprehensive conclusion conclusion conclusion conclusion Cu Cu Cu Cu P P P Pb b b b C C C Cd d d d H H H Hg g g g A A A As s s s C C C Cr r r r

V V V

Conclusions Conclusions Conclusions Conclusions

This paper introduced the designing methods and implication of the agro-environmental information service system based on WebGIS in Jianshui county,Yunnan in details. The relative environmental data were converged together including atmosphere data, soil data, soil heavy metal data, farm irrigation water data etc. in the new system and it offered the costumers a brief and direct interface to obtain valuable agro-environmental information and geospatial information in Jianshui. Besides providing the information inquiring, this system achieved spatial inquire, analyze, and plotting functions between the graphics and attribute data. And also, the new system could accomplish intelligent evaluation on environmental pollution levels, including air pollution, water pollution, soil pollution and soil fertility levels.

The new agro-environmental information service system was applied successfully in Jianshui County. Local agricultural worker, technicians and managements could obtain agricultural or environmental information accurately and directly in time by the system. And the system design process offered other Counties in Yunnan a valuable method and a precedent to build suitable agro-environmental information service system.

Fig. 1 Fig. 1 Fig. 1 Fig. 1 .

 1111 Fig.1 Fig.1 Fig.1 Fig.1. . . . Technique flow diagram of the system development

3 3 3 3

 3 The The The The Implementation Implementation Implementation Implementation of of of of the the the the System System System System 3.1 3.1 3.1 3.1. . . . System System System System Structure Structure Structure Structure

Fig

  Fig Fig Fig Fig. . . .2 2 2 2. . . . Architecture diagram of the system.

  Fig Fig Fig Fig. . . .3 3 3 3. . . . Network structure diagram of the system.

Fig

  Fig Fig Fig Fig.4 .4 .4 .4. . . . Data analysis diagram of the system.

Fig

  Fig Fig Fig Fig.6 .6 .6 .6. . . . The interface of running intelligent evaluation function.

2. 2. 2. 2.2. 2. 2. 2. System System System System Development Development Development Development Platform Platform Platform Platform

Acknowledgments Acknowledgments Acknowledgments Acknowledgments. . . . The findings and the opinions were partially supported by a project of Natural Science Foundation of Yunnan Province --"Design and implementation of county agro-environmental information service system based on WebGIS",NO. 2008ZC050M.This work was supported by Shanghai University, China and Yunnan Agricultural University, China.

Non-spatial database contained four types of ago-environmental information: atmosphere database, soil database, soil heavy metal database, irrigation water database.

Among these databases, there were 9 field names in atmosphere database; they were average geo-temperature, average air-temperature, lowest air temperature, highest air temperature, average wind speed, average relative humidity, sunshine duration, evaporation and precipitation.

There were 14 field names in soil database; they were PH value, organic horizon (g/kg), total nitrogen(N)g/kg, available nitrogen(N)mg/kg, total phosphorus(P)g/kg, available phosphorus(P)mg/kg, total potassium(K)g/kg, quick-acting potassium(K)mg/kg, slowacting Potassium(K)mg/kg, exchangeable magnesium(Mg)g/kg, available molybdenum(Mo)mg/kg, available zinc(Zn)mg/kg, available manganese(Mn)mg/kg and available boron(B)mg/kg. There were 6 field names in soil heavy metal database; they were copper, lead, mercury, cadmium, chrome and arsenic.

There were 17 field names in irrigation water database; they were PH value, cadmium, lead, copper, zinc, mercury, arsenic, chrome, dung coliform group, fluoride, chloride, petroleum, COD, cyanide, total phosphorus, volatile phenol and salt.

3.3 3 3 3 Function Function Function Function Design Design Design Design

Function Design in this System contained 6 main function modules: graphics operation function, spatial data orientation function, environmental data query and analysis function, attribute data maintenance function, processing function on the monitoring data and intelligent evaluation function. (1) Graphics operation function. Jianshui map could be operated with any common browsers. The system could realize zoom in, zoom out, pan, fix zoom, full screen display, roaming, Hawkeye, guidance and other functions.

(2) Spatial data orientation function.

The spatial orientation function could be achieved in electronic map by click, marquee selecting or other query operations.

(3) Data query and analysis function.

The accurately or fuzzy query could be achieved both on spatial data and attribute data. And all users could gain detail information of the selected objects by mouse click or marquee on the electronic map.

(4) Maintenance function.

The system databases could be edited remotely by the system administrators though background operation, which included adding or deleting entity objects and layers, modifying the space position and attribute data of the entity objects and other functions.

(5) Processing function on the monitoring data This new system carried out detailed statistical analysis functions on the obtained spatial and attributes data by WebGIS system. Such as shortest path analysis function, distance and area measurement function, statistical graph generation function of the attribute data and others.

(6) Intelligent evaluation function.

The pollution degree of the ago-environment factors (air, water, soil and soil fertility etc.) could be evaluated intellectually according to the corresponding national standards.


Chunjiang Zhao
email: zhaocj@nercita.org.cn

Shufeng Wang
email: wangsf@nercita.org.cn

Kaiyi Wang
email: wangky@nercita.org.cn

Zhongqiang Liu

Feng Yang
email: yangf@nercita.org.cn

Xiandi Zhang
email: zhangxd@nercita.org.cn

A Localization Algorithm for Sparse-Anchored WSN in Agriculture

Keywords: WSN, localization, Sparse anchors, Multi-hop cooperation

The location information is very crucial for the sensing data in modern agriculture. However, positioning errors and sparse anchors are two key problems that should first be solved for the localization of the sensor nodes. We proposed a novel algorithm to tackle with these challenges. When the system of adjacent anchor distance equations is ill, a minimized-stress search algorithm (MSS) can decrease positioning error greatly. A collaborative sparse-anchored scheme (CSA) has an excellent positioning effect on low density of anchor, specifically on marginal sensor nodes. Our experimental result verified validity and accuracy of the algorithm. It improved feasibility and cost of WSN positioning technique, significantly.

Introduction

Recent advances in micro-electro-mechanical systems (MEMS) technology, wireless communications, and digital electronics have enabled the development of low-cost, low-power, multifunctional sensor nodes that are small in size and communicate in short distances [START_REF] Hautefeuille | A MEMS-based wireless multisensor module for environmental monitoring[END_REF]. These sensor nodes with sensing, data processing, and wireless communicating capabilities can be self-organized together in ad-hoc mode and be deployed in pre-determined or random fashion in inaccessible terrains or disaster relief operations. Therefore there are a wide range of applications for wireless sensor networks (WSN): military, infrastructure security, environment and habitat monitoring, industrial sensing, traffic control, etc [START_REF] Mariño | Viticulture zoning by an experimental WSN[END_REF]. Especially,WSN are applied to varied fields in agriculture to improve the agricultural informatization in recent years [START_REF] O'shaughnessy | Developing wireless sensor networks for monitoring crop canopy temperature using a moving sprinkler system as a platform[END_REF].

In the last decade, WSN have been increasingly applied in modern agriculture [START_REF] Matese | A wireless sensor network for precision viticulture: The NAV system[END_REF].Sensor nodes can be used for monitoring a wide variety of agricultural parameters that include the following phenomena: temperature, humidity, moisture, lightning condition, soil makeup, livestock ID, and so on [START_REF] Siuli Roy | Agro-sense: precision agriculture using sensor-based wireless mesh networks[END_REF]. However, the sensing data is not meaningful without the company of the sensing location. Naturally, the localization of WSN nodes is very crucial for sensing data usage. Furthermore, accurate location might also be useful for routing and coordination purposes in large scale WSN.

The Global Positioning System (GPS) is the most well known location service in use nowadays. The approach taken by GPS, however, is unsuitable for the low-cost, low -power large scale sensor networks nodes in agriculture because of the following reasons: cost, power consumption, inaccessibility, imprecision, size [START_REF] Heraud | Agricultural Automatic Vehicle Guidance from Horses to GPS: How We Got Here, and Where We are Going[END_REF].

It is necessary to develop an alternative inexpensive, more applicable localization approach. This paper will present the novel localization algorithm in sparse-anchored WSN.

The rest of the paper is organized as follows: The next section gives a brief explanation of theoretical background. Section 3 is our proposed algorithm of localization system. Section 4 describes the resolution of the sparse-anchored problem. Section 5 is experimental results and analysis. Finally, section 6 concludes the paper.

Theoretical background

Triangulation, scene analysis, and proximity are the three principal techniques for location sensing [START_REF] Yuan; Law | Construction of local anchor map for indoor position measurement system Zhou[END_REF]. Typically, lateration is the most popular location method that employs triangulation technique. Lateration computes the position of an unknown node by measuring its distance from multiple reference positions. Calculating an object's position in two dimensions requires distance measurements from 3 non-collinear anchors as shown in Figure 1. In 3 dimensions, distance measurements from 4 noncoplanar anchors are required. But, these circles can not intersect at the same point sometime for the error of distance measuring. If an unknown node have three or more neighboring anchors and have measured the distance to neighboring anchors, atomic multilateration can be deployed to determine the position of unknown node. Figure 2(a) illustrates a topology for which atomic multilateration can be applied. The error of estimated position can be expressed as the difference between the measured distance d i and the estimated Euclidean distance (Equation 1). The x and y are the estimated coordinates for the unknown node. According to the minimal mean square estimate (MMSE) [START_REF] Savvides | Dynamic fine-grained localization in ad-hoc networks of sensors[END_REF], i.e. Equation 2, the optimal solution of x and y can be obtained.

If a node has three or more neighboring anchors, an over-determined system with a unique solution for the position of unknown node can be yielded. By setting f i (x,y)=0,squaring and rearranging terms, equation 1 became equation 3.

If unknown node has k neighboring anchors, k equations like equation 3 can be achieved. Then, we can eliminate the 2 2 y x  terms by subtracting the kth equation from the rest, depicted as equation 4.

This system of equations has the form of AX = b and can be solved using the matrix solution for MMSE.

Collaborative multilateration can be deployed in the situation where the number of 1-hop neighboring anchors is less than 3, but multi-hop anchors can provide adequate information to locate the position of the unknown node. Figure 2(b) illustrates a basic example. The unknown node 1 has two 1-hop anchors and two 2-hop anchors through the unknown node 2. We can build the system of linear equations like equation 4 and then obtain the solution of equations using MMSE.

When an unknown node achieved its position using atomic multilateration or collaborative multilateration, it can inform its neighboring unknown nodes that it has become an anchor. If the informed unknown node satisfies the conditions of atomic

2 2 ) i y y ( ) i x x ( i d ) y , x ( i f      (1)    n 1 i 2 i y) (x, f min )) y , x ( min(F ( 2
) ) y x ( d y 2y x 2x y x 2 i 2 i 2 i i i 2 2       (3) ) y x ( ) y x ( d - d )y y - 2(y )x x - 2(x 2 k 2 k 2 i 2 i 2 k 2 i i k i k       (4)
multilateration or collaborative multilateration, it can estimate itself position. This process can be iterative until the positions of all the nodes that can have three or more anchors are estimated eventually. This is iterative multilateration principle.

In this paper, we proposed novel algorithms to improve position error and position ratio under sparse-anchored condition.

Localization algorithm

AH-Los algorithm eliminates the When this common chord lines is parallel to each other, only small error of estimated anchor position can make a very large error of the intersection position. As demonstrated in figure 4, three anchors upside are close to each other and a anchor downside is far from the other anchors, the solution of equations has higher error. Let different anchor equation as the subtrahend, the solution have different error. The red circle represents the real position of the unknown node. Four red asterisks denote four , we can get the system of equations as follows:

) y x ( d y 2y x 2x y x 2 1 2 1 2 1 1 1 2 2       ) y x ( d y 2y x 2x y x 2 2 2 2 2 2 2 2 2 2       (5)
The system of equations has the form of AX =b where

The solution can be solved by b

A ) A A ( X T 1 T  
. At the same time, using

2 2 y x - z delta  
as judge condition, we can judge if the system of equations is ill. When the condition number of the equations is very large, the delta is also very large. This means the position error is too large to locate the node. We proposed the minimized-stress search localization algorithm (MSS) to tackle with this situation.

Before presenting the algorithm, we first make some definitions. Definition 1. The distance between the current position of the unknown (x,y) and the ith neighboring anchor (x i ,y i ) is d icur and the measured distance to ith neighboring anchor is d i .The stress from ith anchor is

) y x ( d y 2y x 2x z 2 1 2 1 2 1 1 1      ) y x ( d y 2y x 2x z 2 2 2 2 2 2 2 2      (6) … ) y x ( d y 2y x 2x z 2 i 2 i 2 i i i                           i i 2 2 1 1 2y , 2x , 1 ...... 2y , 2x , 1 2y , 2x , 1 A   T y , x , z X  and                      2 i 2 i 2 i 2 2
 i F where
As d icur ,> d i , the direction of

 i
F is pointed to the ith anchor from current position, vice versa.

Definition 2. The resultant stress of the unknown,  F , is composed of every component stress

 i F .
The process of the MSS algorithm is described as follows:

Step 1: when the system of equations 6 is ill, we first select two anchors which the distance between them is the farthest and then compute the intersection of two anchor circles which radius is the measured distance from anchor to unknown node.

Step 2: We select each of intersection as search original position and compute the each component stress Step 6: We compare the two final distance residuals and then select the final position with the smallest residual as the position of the unknown node.

The MSS algorithm have overcome the defect of higher position error when the equations is ill-conditioned and conquered the drawback of one starting point that is ease to get in the local minimum. A sample process of MSS algorithm is demonstrated in the figure 5.

          k 1 i 2 i icur y step 0 n x step 0 n ) d (d Xigma F * L y y F * L x x (9)         i 2 1 F ... F F F (8) )) y y ( * ) d / d 1 ( ), x x ( * ) d / d 1 (( F i icur i i icur i i       (7)

Sparse-anchored localization algorithm

After iterative multilateration localization is repeated, The position of the unknown nodes that only have two anchors or one anchor eventually can not be determined We proposed to utilize the collaboration of its one or two anchors to locate the position of the unknown.

Under the condition of only two adjacent anchors, the unknown can estimate itself position U or U', as shown in figure 6. The unknown sent the two possible positions, U and U' to its 1-hop anchors, i.e. A 1 and A 2, and then the one-hop anchors pass the possible positions to the 2-hop anchors, i.e. A 3 .and A 4 .The two-hop anchors will judge if U or U' is in its maximum sensing range, R max . Once either of the two possible positions belongs to the maximum sensing range of A 3 or A 4 by computing distance, the unknown node is informed that this position is excluded from the estimated position because A 3 or A 4 have not been its 1-hop anchor. When each of U and U' can not be excluded, their midpoint is taken as the estimated position. This method can be deployed in the larger scale, such as 3-hop scale or multi-hop scale.

Another case is where the unknown node only has a 1-hop anchor. The previous algorithm will be helpless. We will resort to another method to locate the position approximately. As shown in figure 7, the unknown node has one 1-hop anchor and three 2-hop anchors. The circle with the distance d as radius has six intersection points with the maximum sensing range of three 2-hop anchors, i.e. I 1 , I 2 , I 3 , I 4 , I 5 and I 6 ,. We can compute the distances from the intersection points to three 2-hop anchors, respectively. Once the distance for the intersection point is less than R max (the largest sensing range), the intersection point is excluded. Finally, the intersection points, I 1 and I 6 , are left. So the estimated position is on the pink arc from I 1 to I 6 . We can take the midpoint of the arc or the midpoint of the line from I 1 to I 6 as the estimated position. As this scheme has a larger error, the estimated position should not be taken as anchor in the iterative process.

Experimental results

To verify our proposed localization algorithm, we randomly generate a scenario with 200 nodes within a square field (100x100) in Matlab. These nodes are deployed randomly in the field and can measure the distances to the adjacent nodes in the sensing range R by RSSI or other ranged methods. The anchor ratio to all nodes is A ratio . To simulate real ranged error, the true distances (d) are blurred with Gaussian noise, e r . So the measured distance have the distribution, d*(1+N(0, e r )).

When the transmission range of the nodes(R), the range error(e r ) and anchor ratio (Aratio) is set to 15, 5% and 10%, respectively, the topology is shown in figure 8. The blue triangles represent the anchors, the red circles represent the unknown nodes, and the azury lines represent the wireless connections between the nodes. when there are approximate 9 connectivity degree and 10 percent anchor ratio, AH-Los algorithm can achieve 90 percent position ratio and 6-7% position error (about 20 cm) [START_REF] Greene | Econometric Analysis[END_REF][START_REF] Wang | Self-localization systems and algorithms for wireless sensor networks[END_REF]. But under sparse-anchored conditions, there are higher position error and lower position ratio. Under the same situation, our algorithms have a higher positioning ratio of 100% and lower average positioning error of 2.45%.

Anchor density has a significant effect on the positioning ratio and error. Contrast to the AH-Los algorithm, the positioning ratio was shown with various anchor density in figure 10. As shown, when the percentage of anchors is low, our MS-CSAL algorithm substantially increased the positioning ratio. These algorithms can not only effectively decrease the number of anchors to lower the cost of WSN, but also improve the localizing of the unknown node on the edge of the networks.

Conclusion

We have proposed a novel MSS-CSA algorithm for WSN positioning in agriculture. The minimized-stress algorithm improved the positioning precision greatly when the system of multi-anchors positioning equations is ill. The collaborative sparse-anchored localization algorithm has solved the positioning problem of anchor deficiency, special for the unknown node on the edge of WSN in agricultural positioning. Our simulation experiments have verified the effect of the algorithm in terms of positioning ratio and positioning errors. Our future work will be concentrated on the Zigbee-based implementation and analysis of error propagation in agricultural positioning.

Figure 1 .

 1 Figure 1. Lateration localization scheme. The most classic distributed lateration algorithm is AH-Los algorithm proposed by Andreas Savvides, et al. This algorithm defined three operational primitives: atomic multilateration, collaborative multilateration and iterative multilateration.If an unknown node have three or more neighboring anchors and have measured the distance to neighboring anchors, atomic multilateration can be deployed to determine the position of unknown node. Figure2(a) illustrates a topology for which atomic multilateration can be applied.

Figure 2 .

 2 Figure 2. Multilateration examples

  in equation 3 by subtracting the kth equation from the rest. Essentially, the solution of system is the intersection of common chord equations between ith circle and kth circle. As depicted in figure 3, equations 5 represent 3 circles with each anchor position as center and the distance from the unknown to the anchor as radius. The first equation subtracted from the second equation gives common chord line L1 and The first equation subtracted from the third equation gives common chord line L2. The intersection of line L1 and the line L2 is the estimated position of the unknown node.

Figure 3 .

 3 Figure 3. The intesection of L1 and L2 is the estimated position.

  anchors of the unknown node. Four blue triangles denote the estimated position with different anchor as the subtrahend.

Figure 4 .

 4 Figure 4. Let different kth as the subtrahend,have different error Our algorithm does not eliminate 2 2 y x  term in equation 3. Setting

3 :

 3 Pulled by the resultant stress  F , each estimated position move to new position (x n ,y n) . Next, we judge if the new position have less distance error than the old position As shown by equation 9, x F  , y F  ,Lstep denotes x axis component , y axis component and the steplength for moving, respectively. repeat step 2 for several times. Step 5: when estimated position cannot move on, we turn  F 90 degrees clockwise or 90 degrees counter clockwise to test a new marching direction. If we find a new direction, step 2 is repeated again. Otherwise the process is terminated. So we estimated two possible final positions.

Figure 5 .

 5 Figure 5. The example of MSS algorithm process

Figure 6 .

 6 Figure 6. Localization algorithm with only two 2-hop anchors

Figure 7 .

 7 Figure 7. The Localization algorithm with only one 1-hop anchor

Figure 8 .

 8 Figure 8. The topology with R=15, e r =5% and A ratio =10%.

Figure 9

 9 Figure 9 shows the positioning result of our MSS and CSA algorithms. The starting point of the blue arrows represents the estimated position and the end point of the blue arrows represents the real position. The longer the blue arrow is, the larger the positioning error is.when there are approximate 9 connectivity degree and 10 percent anchor ratio, AH-Los algorithm can achieve 90 percent position ratio and 6-7% position error (about 20 cm)[START_REF] Greene | Econometric Analysis[END_REF][START_REF] Wang | Self-localization systems and algorithms for wireless sensor networks[END_REF]. But under sparse-anchored conditions, there are higher position error and lower position ratio.

Figure 9 .

 9 Figure 9. Final position estimation result.

Figure 10 .

 10 Figure 10. Effect contrast between AH-Los and MSS-CSPL

Acknowledgments.

This work is supported by National 11th Five-year Plan for Science & Technology of China under Grant no. 2009BADB6B02.


Mingming Guo
email: guomingming666666@163.com

Gang Liu

, Xinlei Li

Design and Experiment of Onboard Field 3D Topography Surveying System

Keywords: Laser-controlled Land Leveling, Topographic Surveying, GPS

Laser-controlled land leveling system can obviously improve the planeness of the field and enhance the efficiency of irrigation. The 3D topographic information was needed for project design and evaluation of laser land leveling. In order to obtain the topographic information efficiently, an onboard field 3D topography surveying system was developed. The surveying system consisted of a measuring laser receiver, a GPS receiver, a controller and a hydraulic system. Besides topographic measurement,the system could also achieve laser land leveling. The measuring laser receiver was used to obtain the elevation and the GPS receiver was employed to obtain the longitude and latitude data. The data was fused in the controller to get the 3D topographic information. Field experiments were carried out in different speed and compared with the data from the fixed-point surveying method. The result showed the surveying system had a good consistency with the fixed-point surveying method in slower speed.

Introduction

The application of laser-controlled land leveling technology can achieve high-precision agricultural land leveling and improve the field micro-topographic condition obviously. Therefore, the irrigation efficiency and irrigation uniformity can be increased, resulting in water saving and yield increasing [START_REF] Jf Rickman | Manual for laser land leveling[END_REF].Before and after Laser-controlled land leveling operations, the 3D topographic information was needed in order to develop a reasonable engineering design and evaluation of land leveling [START_REF] Li | Application of GPS Technology in Agricultural Land Leveling Survey[END_REF]. There were many surveying devices for measuring in engineering such as GPS, theodolite, total station, portable computer, etc. [START_REF] Chen | Research and Development on Field Topography Measurement Equipment based on GPS and Laser Techniques[END_REF]. The accuracy and efficiency of measurement can be significantly improved by GPS and laser technology. In cooperation with the Ministry of Land and Recourses, a set of relatively efficiency and low cost portable field measurement system based on GPS and laser was developed by Research Center for Precision Agriculture of China Agricultural University in 2006.The height measurement error was less greater than 4cm, making up the great error of the GPS system in height measurement [START_REF] Chen | Research and Development on Field Topography Measurement Equipment based on GPS and Laser Techniques[END_REF][START_REF] Zhang | Design of 3D Topographic Information Measuring System[END_REF]. But the portable measurement system can only be applied for high precision topographic survey in a small area. A lot of time and manpower will be taken as to a large field and the efficiency will be decreased. Therefore, this study developed a new type of onboard field 3D topography surveying system, providing a kind of effective solution to obtaining the 3D topographic information automatically and saving manpower in large field. At the same time, the system was integrated with function of laser-controlled land leveling, improving the quality and efficiency of ground operations [START_REF] Yang | Research and Development on Field Topography Survey System based on GPS and Laser Techniques[END_REF].

System Analysis and Design

A modular and integrated design concept was adopted. The system was divided into four separate parts: laser measurement system, GPS receiver, controller and hydraulic system. The structure was shown in Figure 1. Laser measuring receiver will receive the laser signal and send to the controller after treatment. Controller, as the controlling terminal and information processing platform, was responsible for gathering the information of GPS horizontal coordinates and elevation information of laser measuring receiver ,display and storage, controlling the hydraulic system according to the position signal of receiver. Hydraulic control system will control the raise and lower of leveling bucket according to the output signal of the controller,realizing land leveling operation.

System Implementation

3.1Design of measuring receiver

Laser measuring receiver was an important part of onboard field 3D topography surveying system. Laser transmitter fired laser beam to form a base level above the working plane. Signal was produced and sent to the controller after the laser measuring receiver received real-time weak low-frequency laser beam.

The working principle of the laser measuring receiver was shown in Figure 2.Combanation filter was composed of red organic glass and interference filter. Red organic glass was used as the in-light window, which could greatly reduce the background light into the laser measuring receiver. Interference filter was used at the laser measuring receiver to further reduce the background light. Photo-electric cells were used to transform light signal into electrical signal. The low-noise preamplifier and main amplifier based on integrated amplifier were used to amplify the weak electrical signal effectively. The wave shaping circuit was employed to achieve better signal conditioning from spike pulse signal to digital TTL signal. The widening circuit was used to stretch the pulse width in order to be processed by the follow-up circuit more easily by the controller [START_REF] Lv | Improvement and Experimentation of Laser Controlled Land Leveling System[END_REF].

Fig.2. Principle of measuring laser receiver

In order to achieve the requirement of effective laser signal receiving angle to 360 °, the research formed rational design of spatial distribution of the cells, which was shown in Figure 3. 128 pieces of dimension 20mm × 5mm photo-electric cells were divided into 32 layers and 4 rows. In each receiving layer,adjacent photo-electric cells were fixed vertically at the same height on two metal holders merged in square shape and can meet the requirement of effective laser signal receiving angle to 360 ° [START_REF] Lin | Research and Development on Receiver and Controller for Laser Controlled Land Leveling System[END_REF].

Each column of adjacent photo-electric cells were installed at an interval of 2mm in order to get the vertical measurement range to 70.2cm, while 32 pieces of photo-electric cells composed 32 groups of signals, corresponding height degree scale to 63,meeting the requirement of precision measurement on elevation information.

The option of GPS receiver

Considering the effect of the speed to the accuracy of GPS, the research set GPS port on standard of RS232 form. Different GPS measurement equipment, such as GPS OEM board, high precision RTK DGPS receivers can be chosen to meet different requirement of measurement accuracy.

Controller

Controller was the monitoring and operating center of onboard field 3D topography surveying system. The paper designed a controller with two modes of measurement and land leveling. The functions of the modes were shown as follows:

(1) Measurement mode: receive and parse the GPS data, receive signal from the laser measuring receiver and calculate the relative elevation, display 3D information, data storage, indicate relative position of the receiver with LED indicator and LCD screen;

(2) Land leveling mode: control hydraulic system to achieve the raise and lower of the leveling bucket according to the signal of the laser receiver, instruct the relative position of the receiver, achieve modes witching from manual to automatic.

Design of the controller's hardware

The research adopted ARM7 as CPU for the controller and the hardware circuit was shown in Figure 4. In measurement mode, the controller fused the data gathered from laser measuring receiver and GPS OEM board so as to get the 3D information of the topographic measurement point, stored date using U disk storage module, indicated the state of the system through LCD screen. In land leveling mode, the controller switched the signal from laser measuring receiver into control signal to hydraulic system and dominated the raise and lower of the leveling bucket, realizing land leveling.

Design of hydraulic system

Hydraulic system was mainly used to control the movements of the leveling bucket in order to achieve land leveling. The hydraulic control system accepted signals from the intelligent controller and would supply oil to raise or lower the leveling bucket automatically to maintain the laser receiver on right position [START_REF] Si | Development and Experiment on laser land Leveling System[END_REF]. The hydraulic system required quick response speed and high control precision, so it was a major problem to matching the system to the controller. The desired rate at which the bucket raise and lower would depend on the operating speed. The faster the ground speed the faster the bucket would need to adjust. A remote relief valve was used before the control valve; the pressure setting on this valve would change the raise/ lower speed. The principle of hydraulic pressure controller was shown in Fig. 6.

Field experiment 4.1 Experiment materials and methods

In April 2010, at Experimental Station of China Agricultural University, a field at the length of 70m and width of 60m was chosen and East Red 754 tractor was selected as traction power.3D topographic survey experiments were taken respectively in speed of 20km / h and 10km / h. The experiment selected AgGPS132 as the GPS receiver and applied portable 3D topographic survey system developed by the Precision Agriculture Center of China Agricultural University as a comparison. The test placed the antenna of GPS and radio station on the leveling bucket with magnetic sucker in order to receive differential position information. The laser measuring receiver was installed at a suitable location on the mast of leveling bucket for the purpose of receiving laser signals.

Experiment Results

The relative elevation of ground statistics eigenvalues measured by the portable survey system from fixed-point and two-vehicle speed were shown in Table 1.Compared with fixed-point measurements, the maximum relative elevation difference obtained from fast speed(20km / h) and slow speed (10km / h) reached to 3.7cm and 1.5cm respectively. The minimum difference reached to 1.6cm and 0.5cm respectively. The average deviation attained to 0.6cm and 0.5cm, while the standard deviation got a small deviation. As the difference between the number and the location of measurement points, it was difficult to analyze statistical data rigorously at the same point and the onboard state measurements. But to the whole landscape, the small difference of standard deviation can be reflected from the 3D topographic map in Figure 7. The difference on elevation at the edge of the field was mainly caused by large bumps when the tractor steering to the place, resulting in laser signal exceeded the range of laser measuring receiver and lost the measuring points. The relative elevation of ground Statistics eigenvalues from Table 1 showed that the maximum relative elevation difference was 2.2cm and the minimum relative elevation difference was 1.1cm,while the average value and standard error were approximate,which meant the measurement in different speed had a big influence on extremum and little effect on characteristics of the overall landscape. Even so, the influence of speed to the measurement result can be seen from Figure 8.It was a Statistical chart of percentages of the absolute difference >2cm between elevations and their average values. It was clear that the percentage accounted in fast speed was bigger than in the slow speed. This showed that the measurement result got from fast speed had much more discrete data and the accuracy in slow speed was greater than fast speed.

Tab.1 Experiment results

Statistics

Conclusion

This paper presented a new type of onboard field 3D topography surveying system.

The experiment result indicated that the influence of the tractor's speed to the measurement accuracy was obvious and the measurement accuracy in slow speed was greater than in the fast speed. Different speed should be adopted according to the field condition when doing measurement with onboard field 3D topography surveying system. Slow and uniform speed was important to guarantee the measurement accuracy.

Fig. 1 .

 1 Fig.1. Structure of onboard field 3D topography surveying system

Fig. 3 .

 3 Fig.3. Distribution of photo-electric cells in horizontal direction

Fig. 4 .

 4 Fig.4. Hardware circuit diagram of controller

Fig. 5 .

 5 Fig.5. Diagram of system task

1 -Fig. 6 .

 16 Fig.6.Principle of hydraulic pressure controller

Fig. 7 .

 7 Fig.7. Comparison of 3D topographic map for field survey by fixed-point and in different moving speeds

Fig. 8 .

 8 Fig.8. Statistical chart of percentages of the absolute difference >2cm between elevations and their average values under two moving speeds

Acknowledgement

This research is sponsored by the project 2008BAB38B06 and 2009BAC55B01. All of the mentioned support is gratefully acknowledged.