Elsa Cariou
email: elsa.cariou@univ-nantes.fr

Agnes Baltzer
email: agnes.baltzer@univ-nantes.fr

Donatienne Leparoux
email: donatienne.leparoux@univ-eiffel.fr

Vincent Lacombe
email: v.lacombe@digiscan3d.fr

Giuseppe Zappalà

Jesus Martinez-Frias

Collaborative 3d Monitoring for Coastal Survey: Conclusive Tests and First Feedbacks Using the SELPhCoAST Workflow

Keywords: smart devices, structure from motion, participatory 3D monitoring, coastal erosion, soft and nature-based solutions

Structure from Motion" by smart devices photography (SfM-S) is a current promising tool to support 3D participatory monitoring of heritage and geosites. Within the ODySéYeu scientific project, which aims to analyze the sedimentary dynamics around the isle of Yeu (France), a consortium of different local actors was invited to collectively develop an integrated solution to monitor the coastal evolution of the isle in 3D. This new solution is composed of a combination of an application (SENTINELLES de la côte) and a specific workflow (SELPhCoAST), which guides citizens to acquire reliable in-situ photo datasets with their own smart device, facilitates data transmission, and allows both a reliable data treatment and a public presentation of matters and results. This study presents the results of reproducibility and accuracy tests performed on a test-site to validate the SELPhCoAST workflow, over 20 months of monitoring, with multiple operators and devices. Tests show that at least 95% of each SfM-S model is identical to the terrestrial laser scans models within a range of ±5 cm, almost independently of the operator or smartphone model. This study highlights the interest of this cost-effective participatory solution to understand coastal erosion processes, and facilitate the establishment of soft and nature-based solutions of protection, management or restoration of sites.

Introduction

Coastal erosion is a complex mechanism driven by multiple factors, combining each other at different time scales. All sites are not equally exposed to waves, currents, weathering or human activities, and the response of impacted coasts depends on their own nature and history. Thus, managing coastal erosion is not limited to prevent wave action. Indeed, establishing efficient nature-based protection solutions and relevant "red lines" against risks requires a site per site analysis, discriminating factors, identifying their temporal and spatial distribution, and estimating their relative impact.

Too simplistic visions of erosion and engendered risks, from both leaders, builders and local population, often lead to expensive and ineffective management choices. In the current context of climate change associated with increased coastal frequentation and limited financial resources, such errors can no longer persist. An appropriate way to improve coastal management is to promote a better mix and sharing of scientific and local knowledge, associating local actors to observation and monitoring of sites identified as risky. This requires appropriate tools to facilitate data and results dissemination, but it appears to be very effective since more sites can be monitored and more actors will finally share a common improved knowledge of risks, matters and potential nature-based solutions.

In France, a first participatory application (RIVAGES) was created in 2017, to monitor coastal movements basing on smartphone GPS data [START_REF] Cerema Website | Rivages»: Application Smartphone du Suivi des Relevés du Trait de Côte[END_REF]. This application and its workflow are dedicated to long-distance monitoring along continuous shores. They allow tracking large regional-scale erosion processes. Where sites are small, disconnected and submitted to meter-scale erosion events, the sensitivity of smartphones GPS becomes insufficient, and 2D data are too limited to describe processes precisely. Thus, in such cases, 3D reconstructions appear to be much more powerful, but until this last decade, they required expensive professional technics, hindering possibilities of frequent and participatory surveys. The development of structure from motion (SfM, see Table 1 for all acronyms) and programs able to semiautomatically reconstruct 3D models, basing on simple photographs, were a first major step on this pathway [START_REF] Westoby | Structure-from-Motion' photogrammetry: A lowcost, effective tool for geoscience applications[END_REF][START_REF] Wróżyński | Ground volume assessment using 'Structure from Motion' photogrammetry with a smartphone and a compact camera[END_REF]. Recently, some studies have demonstrated that medium and high quality smartphones, and tablets or digital cameras, provide photographs (or images extracted from videos) usable to reconstruct relevant topography models [START_REF] Micheletti | Investigating the geomorphological potential of freely available and accessible structure-from-motion photogrammetry using a smartphone[END_REF][START_REF] Micheletti | Structure from Motion (SfM) photogrammetry[END_REF][START_REF] Jaud | Potential of Smartphone SfM Photogrammetry to measure coastal morphodynamics[END_REF] and to monitor volumetric changes [START_REF] Wróżyński | Ground volume assessment using 'Structure from Motion' photogrammetry with a smartphone and a compact camera[END_REF][START_REF] Westoby | Cost-effective erosion monitoring of coastal cliffs[END_REF].

However, community-based environmental monitoring and information systems, based on citizens' own devices (e.g., smartphones, laptops and tablets) remained "perspectives" until now [START_REF] Jaud | Potential of Smartphone SfM Photogrammetry to measure coastal morphodynamics[END_REF], for those main reasons:  Three-dimensional models obtained by SfM-S ("Structure from Motion" by Smart devices photography) have no native absolute dimensions and over/underestimate distances heterogeneously, generating deformation and bad scaling. This phenomenon is amplified when the dataset is insufficient [START_REF] Wróżyński | Ground volume assessment using 'Structure from Motion' photogrammetry with a smartphone and a compact camera[END_REF];  Geotagged photographs produced using GPS chipsets data of smart devices do not provide a sufficient accuracy to correct such deformation and reconstruct relevant 3D models. Thus, most of developed protocols finally use additional RTK DGPS measurements and require additional professional tools during the fieldwork acquisition [START_REF] Jaud | Potential of Smartphone SfM Photogrammetry to measure coastal morphodynamics[END_REF]; 

The number of pictures required to obtain a relevant 3D model by SfM is high and transmission of field data from the smart device of the operator to a computer server can be difficult, especially for inexperienced operators [START_REF] Chidburee | Towards a Low-Cost Real-Time Photogrammetric Landslide Monitoring System Utilising Mobile and Cloud Computing Technology[END_REF];  Routine data processing requires being optimized and automatized to be cost-effective and extended to numerous sites;  Integrated tools, facilitating interactions between participant citizens, people able to interpret data and coastal managers were still lacking. ODySeYeu is a research program initiated in 2018 and aiming to develop collaborative protocols and tools to monitor and understand environmental dynamics around the isle of Yeu, located westward middle French Atlantic coast (Figure 1). A consortium of partners, involving a multidisciplinary academic scientific team, the municipality of Yeu, four local associations, two schools and two local companies, manages the program. In a coelaborative approach, the consortium was invited to design collectively a collaborative solution to monitor, in 3D, the development of erosion along 9 sites, where major coastal risks had been identified by the municipality and the scientific team.

Expectations of the different actors were listed (Figure 2) and the two partner companies DIGISCAN3D (specialist in 3D measurement for industry and cultural heritage, 4 rue des Tuiliers, ZA de Viais, 44860 Pont-Saint-Martin, France) and Studio MATAVAI (specialist in web application development, 24 rue Georges Clémenceau, 85350 île d'Yeu, France) were challenged to develop and set up respectively:  For DIGISCAN3D: a workflow called SELPhCoAST (Suivi d'Environnements par Lasergrammétrie et Photogrammétrie Collaborative Assistée pour Smartphones et Tablettes), based on SfM-S data treatment. To respect the established specifications, the solution had to enable the 3D monitoring of sites up to 100 m wide, with a stable and high accuracy of results (the tolerance range was set to ±50 mm by comparison with professional tools). The workflow also had to include a rapid and simple photo acquisition protocol for inexperienced operators in the field (including an optimized number of photographs per site). Furthermore, the visual impact of the solution in the field had to be extremely reduced because four of the monitored sites are situated in a protected and classified site (no targets and no marks if possible). Finally, treatment also had to be cost-effective for the territorial collectivity partner (less than €5000, per year and per site, for a monthly monitoring).



For STUDIO MATAVAI: Specifications for an application designed for smartphone and tablets. This multiplatforms application, named SENTINELLES de la Côte, should (i) enable the ODySeYeu team to guide citizens in operating the SELPhCoAST acquisition protocol in the field, through a free of charges and user friendly application, (ii) operate data transmission to DIGISCAN3D and the scientific team and (iii) be interactive and facilitate dialogue between users and the ODySéYeu team (observation, information, remarks or interrogations sharing in both ways). At the same time, the ODySéYeu team is committed to upload regularly public new 3D models (interpreted and annotated), based on photographs datasets provided by participant citizens, on Sketchfab® (public free-access online 3D visualization platform, sketchfab.com, 30 December 2020). SELPhCoAST is a protected workflow, property of DIGISCAN3D Company. This paper describes how the ODySéYeu academic scientific team tested the workflow to validate metrology, reproducibility and robustness of results and the operability of the protocol, when used in the field by inexperienced operators with different devices. This article also presents and discusses the results of the first 20 months of semiparticipatory monitoring (test phase) for the site of Ker Châlon.

Study Area

Yeu is an inhabited island located at 23 km from the French west coast. Geologically, the isle is formed by an asymmetric anticlinal structure of the Armorican gneiss bedrock. This large NW-SE fold, and the subsequent foliation of gneiss, impact the morphology of the island and divide it into two characteristic types of coasts: the SE coast, exposed to Atlantic swells and displaying meter to decameter-scale gneiss cliffs, and the NE coast, turned landward and much protected from swells. This coast is characterized by a succession of adjacent systems of beaches, dunes and coastal marshes (from 10 m to 2 km wide), following major geological structures and separated by rocky points. Differential erosion of the two types of coasts was estimated from the 50s to 2011, highlighting chronic erosion along some sectors of the NE coast, with speeds around 1 m/yr [START_REF] Juigner | Géomatique au Service de L'observation du Trait de côte-Contribution à L'étude des aléas Côtiers sur les Littoraux Dunaires de la Région Pays de la Loire[END_REF]. Discriminating anthropogenic responsibilities in this erosional process is difficult but the extensive extraction of sand, peat and gravel, on beaches and dunes, and the successive extensions of the harbor across the 19-20th centuries are obviously involved. Daily human activities also have a clear impact because five thousand people live permanently on the isle and about three hundred thousand visitors come each year for durations from a few hours to a few months. Thus, sandy coasts are extremely solicited and exposed to different permanent or seasonal human activities (upkeep of public networks and facilities, fishing, building, tourism, etc.).

In 2014, successive storm events increased erosion in many sectors all around the island. The sand of some western pocket beaches entirely migrated to the foreshore, which had never been seen before according to old memories. Sand cliffs appeared in many sites along eastern and northern coasts. Since 2014, relatively favorable weather conditions allowed to get sand back on western pocket beaches, highlighting their high resilience ability. A few dunes also seem to grow again, but erosion always seems predominant in most of the eastern and northern sectors. Along the eastern coast, erosion is becoming more and more preoccupying because of exposed buildings. Some major public infrastructures, facilities and networks are being exposed too. In particular, water and electricity supply pipes and cables land at different places along this coast, and are buried along large portions of this coast, before joining distribution infrastructures (Figure 1).

To experiment the participatory monitoring, nine sites related to major issues (heritage, public networks, buildings, etc.) were chosen along the eastern coast by the ODy-SéYeu consortium. Four sites lay within a classified area, justifying the major constrain of a minimal visual impact of required infrastructures if needed. All sites display at least a few "inert areas", such as outcropping bedrock or sealed reinforced concrete. Site extent never exceeds 100 m for 5 m high. The site of Ker Châlon was chosen here to illustrate tests performed to challenge the SELPhCoAST workflow. This site shows the most complex morphology (two eroded lobs and large screes, generating reverse angles (Figure 1). Its size (30 m wide, 4 m high and 5-11 m deep) enables to challenge the produced morphological reconstructions in the three space dimensions. This site is also a very good example of mixed issues and problematics because it is situated in the middle of a crowded beach. During spring tides, waves reach the cliff base. The outcrop is composed of sand and bedrock at the base, successively overlapped by a palaeosoil of unknown prehistoric age, a sand dune and an old building of the 17th century (probably a building belonging to the first coastal defense system built on the island, according to the municipality heritage service). Finally, the positive relief of the site directly protects from the sea a recent building, parking and the main water supply pipe, all situated less than 50 m backwards. A dozen of habitations are also concerned within a radius of 100 m.

Materials and Methods

Modus Operandi

This section describes the four tests proceeded in order to challenge the robustness (accuracy and reproducibility) of the SELPhCoAST workflow when processed by inexperienced operators, using their own smart devices.

Tests 1 and 2: Variability of Results Depending on Smart Devices and Operators

The first test was conducted on 20 th August 2018 on the site of Ker Châlon. This day, a first terrestrial laser scanner survey was performed on the same site, to produce a "reference 3D model" (see Section 3.2). A few days before this date, volunteers had been recruited on the ODySéYeu Facebook page, proposing followers to participate to a new participatory protocol, designed to enable citizen to participate to coastal erosion monitoring. On the 20/08/2018, five inexperienced volunteers joined the ODySéYeu team in the field, with their own smartphone (see the list and technical characteristics in Table 2 and Section 3.3), to test the SELPhCoAST protocol. A few instructions were given to guide them during the acquisition of 54 photographs, simulating the guidelines given by a hypothetic future participatory smartphone application (i.e., Sentinelle de la Côte). For each participant, the operation lasted between 15 and 30 min, including the presentation speech and the acquisition. Photographs taken by volunteers were collected and processed by DIGISCAN3D, to reconstruct one SfM-S model per smartphone. Then all SfM-S models were compared to the reference model (test 1, see Section 3.4 for details about comparisons).

In order to increase the range of tested smartphone qualities and configurations, an additional test (test 2) was performed during the Science Festival of 2019, on 5th October 2019. Eight new smartphone models (see Table 2 for technical characteristics), manipulated by new inexperienced operators were tested this day, on the eight other sites monitored in Yeu. Obtained models were compared to TLS models of these sites, following exactly the same modus operandi as in the test site of Ker Châlon.

Test 3: Reproducibility of Results and Long-term Survey

Since the 20 August 2018, six SfM-S surveys were performed on the site by two volunteers following the SELPhCoAST protocol, over 20 months. Datasets were processed by DIGISCAN3D following the workflow too.

During the 20 months survey, an additional TLS model was also produced on May 2019, in order to ensure a classic low temporal resolution monitoring of the site and prevent any kind of drift or dysfunction of the SELPhCoAST workflow.

Test 4: Final Revision of the Protocol

The experience of the 20 months-long survey and the first creation phases of the SEN-TINELLES application, lead the consortium to conduct a final phase of revision and optimization of the SELPhCoAST workflow in March-April 2020. The new version of the workflow includes treatment improvements, which allowed decreasing drastically the number of required photos (from 54 to 33 for the site of Ker Châlon). In order to test the efficiency of those last improvements, a final TLS acquisition was performed on the site of Ker Châlon, and doubled by a simultaneous SfM-S acquisition, using the revised field acquisition protocol. Obtained models were compared (Test 4).

Terrestrial Laser Scanning (TLS)

In order to compare all SfM-S models produced with the SELPhCoAST workflow, and to test their accuracy, we provided a "reference model" to each site monitored in the ODySéYeu project, using a TLS device FARO® Focus S70 (Lake Mary, Florida, USA). This device scans within a sphere of 70 m radius, and each scan covers 360° horizontally and 270° vertically. The FARO® Focus S70 creates a dense point cloud by analyzing the phase shift of the emitted laser beam beating a hard surface. According to FARO specifications, the estimated error in measuring the distance from a point to the source is lower than a millimeter within the 10 first meters from the source and estimated to 3.5 mm at 25 m. Points scanned beyond 25 meters from the source were not taken into account during reconstruction processing of the model, to keep an accuracy of data lower than 3.5 mm for each point of the reference model. The scanner also captures color by taking high definition pictures and applying an exposure correction (high dynamic range).

In order to capture the entire relief of the site of Ker Châlon, ten distinct stations of scan are necessary, each separated by 10-20 m. The ten distinct point clouds obtained per field acquisition are realigned together using the FARO SCENE software (version 2018), to produce a global dense point cloud of 88.4 million points describing the topography of the entire site. Then the final cloud is imported in the 3DReshaper software (version 2017) to produce a textured mesh of several million polygons. All TLS data were processed the same way. Final polygon meshes were used for shape comparisons.

Cameras

Although previous studies already predicted the independence of SfM-S models accuracy with respect to the smartphone model [START_REF] Jaud | Potential of Smartphone SfM Photogrammetry to measure coastal morphodynamics[END_REF], it was necessary to multiply tests with a maximum of models with different qualities and photo treatment processes, to identify and prevent possible vulnerabilities of the SELPhCoAST workflow. On the 20/08/20, five different smartphones were used simultaneously to the TLS (Table 2). Samsung Galaxy ® A3 (8 Mpx), Samsung ® Galaxy S7 (12 Mpx) and Sony ® Xperia XA1 (12 Mpx), are considered as midrange smartphones. Huawei ® P20 Pro and Apple® iPhone X are upmarket devices. On the 05/10/19, 8 additional smartphone models, from mid-range to low-range devices, were also tested (Table 2). Finally, a Samsung ® Galaxy S7 and a Huawei ® P20 Pro were used to perform the regular monitoring of the test site up to 2020.

Comparison of Models

All SfM-S models, obtained on 20 th August 2018, were separately compared to the reference TLS model obtained the same day, using the GOM Inspect Pro software (version 2019). Each one was firstly scaled, using few remarkable points of the bedrock, present in both TLS and SfM-S 3D models, to create reference distances. Then eight distinct rocky zones, from dm 2 to m 2 , distributed all over the model, and considered as inert, were used to proceed a best fit alignment between each SfM-S model and the TLS reference model. Then, in order to quantify possible deformations introduced by the SfM-S reconstruction and scaling, a shape comparison was performed using a "point-to-point distance" tool, and computing nearest-neighbor distances between homologous triangle vertices of the reference TLS and compared SfM-S 3D model. For each model, values of standard deviation (SD) and the histogram of differences between models were calculated and plotted by the software along five distinct large zones, including rocks and sand, but avoiding vegetated areas, in perpetual motion. Finally, obtained results were compared for all models and confronted to smartphone technical characteristics.

The same comparison workflow was processed to compare anachronous models to the reference TLS 3D model (20/08/18), which was considered as the original state for monitoring and used as validation data to assess accuracy of SfM-S models during the 20 months survey. Models were scaled using each time different remarkable points of the bedrock, to ensure nondependence to scaling. Produced SfM-S 3D models were aligned by best fit, using each time different bedrock surfaces, distributed homogeneously across the site, in order to test a possible variability induced by the choice of surfaces for aligning models. Other inert parts of the bedrock were used to validate good positioning of SfM-S models on the reference model and confirm reliability of results.

Results

Comparison Between Tls and Sfm-S Meshes Obtained the Same Day from Different Smartphone Photograph Datasets (Tests 1, 2 and 4)

The first test compares the TLS model performed on 20 August 2018 to the five 3D reconstructions of the site produced using smartphones photographs, on the same day (Figure 3).

All datasets led to the reconstruction of a point cloud (Table 2). On sandy and rocky parts considered as inert during the test (Figure 3a,b), more than 70% of the surface captured by the TLS was also reconstructed in each SfM-S model, highlighting high rates of reconstruction with the workflow, independently of the smartphone model used or the operator.

Figure 3b-g presents surface comparisons between the reference TLS model and each

SfM-S model. Along inert zones chosen for the test (Figure 3b), the mean distance between the TLS model and SfM-S models ranged from 2.60 to -0.27 mm (Figure 3c-g), and all smartphones present very similar normal patterns of distribution of distances to the reference, along inert zones (Figure 3b), except the Huawei P20 Pro, which shows a slightly wider distribution. Standard deviations calculated on these areas ranged from 14.95 to 22.25 mm, depending on the model (Figure 3c-g). According to those values, more than 99.7% of points (3SD) were within the tolerance range of ±50 mm for models Samsung® Galaxy S7 and Apple ® iPhone X and more than 95% of points (2SD) were in the tolerance range for the three other models. Along entire models (Figure 3c-g), histograms of differences between the reference model and SfM-S model show that the ±50 mm tolerance range was also respected on entire models, except in areas covered by dense vegetation, which of course were moved by the wind between TLS and photo acquisitions, and appeared randomly in red, blue or yellow on plots. Like on inert parts, the Huawei P20 Pro showed a slightly wider distribution of distances to the reference than other smartphone models on the entire model, but remained within the tolerance range at 95%.

Results of comparisons obtained in other sites on 5 October 2019 are compiled in Table 2 (Test 2). Datasets produced this day generally allowed the production of relevant SfM-S models, within the tolerance range at 95% or 99% on rocky inert parts. Only pictures produced by an Orange ® Rise 30 and a Samsung ® J3 (used with a degraded resolution) did not allow producing useful data.

After revision of the workflow (Test 4), comparison of the two TLS and SfM-S models performed on 7 th April 2020 shows a mean distance between reference and SfM-S model of 0.76 mm and a standard deviation of 11.5 mm over the whole inert parts (sand + bedrock) selected (Figure 4). Over the same areas, the percentage of surface reconstructed on the SfM-S model by comparison to the surface captured by the TLS reach 86.8%.

Monitoring Surveys (Test 3)

Computation of the comparison between the reference TLS model (20 th August 2018) and the eight successive models acquired both by SfM-S and TLS over the 20 months survey shows the morphological evolution of the test site (Figure 5). Mean distances to the reference range from 5.6 to 0.04 mm on the inert zones (bedrock only). Standard deviations range from 20.87 to 12.69 mm on the same zones. On the contrary, huge differences were locally recorded on "mobile areas" (sandy or vegetated), showing a differential evolution of the morphology. Maximum erosion was recorded in the upper right corner of the four last models (deep blue areas repaired by ε' on Figure 5e), with values up to -1200 mm. Maximum accretion was recorded just below maximum erosion zones (large deep red area in models 5-8, repaired by ε'' and ε''' in Figure 5g-h), with maximum values up to +350 mm. This erosion/accretion vertical couple typically highlights a collapse of material. According to GOM Inspect Pro software, the collapsed volume in this sector is estimated to be about 2.5 m 3 . Other erosion/accretion zones were also recorded along the rest of the sand cliff but were not comparable in extension or volume. Sand dynamics of the upper beach was perfectly visible (examples repaired by γ and γ' on Figure 5a,g), showing sand moving back forth, with creation of ephemeral depressions (up to 300 mm deep) and bumps (up to 170 mm high).

Discussion

Validation of the Workflow

During the two participatory experiments of 20 August 2018 and 5 October 2019, and during the 20 months of semiparticipatory monitoring, our team observed and tested the operability of the entire workflow, from the first participatory acquisition step to the last step of using produced data to inform population and decision makers. Results presented here confirm that the workflow proposed by DIGISCAN3D allows inexperienced citizens producing reliable data to monitor local erosion. In the field, volunteers were surprised by the simplicity and entertainment of the acquisition (around 5 min for inexperienced volunteers, less than 3 min for experienced ones). We also observed that children from 6-8 years old, accompanied by an adult, could perform acquisitions and quickly became independent in proceeding.

Independent of the operator or the smartphone model considered, more than 70% of the TLS reference model is always reconstructed in SfM-S models. More than 95% (2SD) of points of each SfM-S model were also closer than 50 mm to the TLS reference model, and mean distances observed (on inert parts) were within the error range of point positioning indicated by the TLS producer (around 3.5 mm at 25 m). Finally, comparison of SfM-S models over 20 months also shows an excellent reproducibility of measurements on inert parts of the site, highlighting the stability and reliability of the process in time. Recent improvements made in the photoacquisition protocol further improved the accuracy and operability (Figure 4). Mean distances to the reference and standard deviations appeared equivalent or more accurate than most recent published examples using classical GCPs and DGPS devices, or not [START_REF] Westoby | Structure-from-Motion' photogrammetry: A lowcost, effective tool for geoscience applications[END_REF][START_REF] Wróżyński | Ground volume assessment using 'Structure from Motion' photogrammetry with a smartphone and a compact camera[END_REF][START_REF] Micheletti | Investigating the geomorphological potential of freely available and accessible structure-from-motion photogrammetry using a smartphone[END_REF][START_REF] Micheletti | Structure from Motion (SfM) photogrammetry[END_REF][START_REF] Jaud | Potential of Smartphone SfM Photogrammetry to measure coastal morphodynamics[END_REF]. For all these reasons, the ODySéYeu consortium validated the SELPhCoAST workflow, and considered that it fulfills all its initial requirements in both guiding inexperienced operators in the field and producing accurate 3D models for a reliable erosion monitoring. Furthermore, the results obtained during the different tests revealed interesting issues, developed in the two paragraphs below.

Smartphone Dependence

As already mentioned by Jaud et al. (2019) [START_REF] Jaud | Potential of Smartphone SfM Photogrammetry to measure coastal morphodynamics[END_REF], the quality of reconstructed surfaces seems poorly dependent of the smartphone model. All produced datasets allowed reconstructing acceptable SfM-S models, except for the Orange® Rise 30 and the Samsung J3 (Table 2). For this last model, the owner had deliberately lowered the resolution of images produced by his phone. This experiment may indicate that smartphones with poorly sensitive cameras (less than 5 MPx), and any other smartphones configured to produce downsized photos, were not appropriate to realize this kind of monitoring. More surprisingly, the "worst" mean distances and standard deviations obtained during tests on 20 August 2018 were obtained with the midrange Sony® Xperia XA1, equipped with a 23 MPx camera and the high-end smartphone Huawei ® P20 Pro.

The meticulous observation of the model in Figure 3f showed that the highest differences between the TLS model and the SfM-S model obtained with the Sony® Xperia XA1 were concentrated in parts of the site situated in the shadows. Then, comparing the resolution of photographs provided by the device at the end of the test (3840 × 2160 = 8 MPx) and the native resolution of its camera (23 Mpx), revealed the action of an "aggressive" preprocess, that reworked pixels to lower the size of native pictures before recording them on the phone. This autodegradation of data seems to affect particularly dark areas. The situation is rather similar for the Huawei ® P20 Pro, which is equipped with a complex system of three camera sensors combined to an artificial intelligence (AI), which preprocesses photographic data to "embellish" produced photos. The AI automatically rearranges pixels (pixel binning) and this intervention seems to disturb SfM-S surface reconstruction. For those two smartphone models, disturbances generated by IAs are finally minor but they increase mean distances to the reference and standard deviation and make the 3 × SD value higher than the symbolic preset "±50 mm" value (Figure 3). When the Huawei ® P20 Pro was used to monitor the morphological evolution of the site (on 29 November 2019 and 3 February 2020), the IA was manually inactivated before photo acquisition (for the case of 07/03/20, see discussion below). Thus, SD calculated on inert parts significantly decreased (respectively 12.89 mm and 13.75 mm), making the models perfectly acceptable and demonstrating the responsibility of the IA in degrading native datasets. This point is very important for a participatory perspective, because if these kinds of photo preprocessing tend to generalize to all smartphones in the future, it could hinder the use of SfM-S. At least, smartphones using such IAs should be identified/listed. Hence, to be user-friendly, applications guiding participatory photo acquisition for SELPhCOAST should include the automatic inactivation of any IAs and resizing preprocessing, because modifying photo acquisition parameters of its own smartphone is not trivial to all users.

Inert Parts Dependence

The use of natural inert parts of the site to align chronological models is a clear advantage of the SELPhCoAST workflow, especially in the context of a protected classified site, because targets or ground mark have a significant visual impact and can arouse the attention and curiosity of some people, leading to an undesirable increase of frequentation nearby fragile areas. However, the absence of targets or marks requires in turn the permanent presence of visible, and strictly inert areas (at the scale of decades of years) within monitored sites. In Yeu, the frequent presence of bedrock outcrops along the coast is very convenient. However, on the model produced on 7 March 2020 (Figure 5g), the downgrading of mean distance to the reference and SD clearly highlight a high dependency to inert parts clearness. Indeed, that day, sand and algae partly covered the base of the site. This punctual cover impacted several zones usually considered as inert and chosen to control alignment of models. We tried to isolate and ignore these covered zones for the control but despite our efforts the mean distance and the standard deviation measured were clearly affected, suggesting that some "dirty parts" remained unnoticed. Here, consequences are minors but this phenomenon highlights the importance of having enough large and permanently clean inert areas in monitored sites to ensure the quality of alignments and controls, whether they are natural or not.

High Frequency, High Space Resolution Monitoring

On the contrary of a classic annual survey, the frequent participatory surveys offer a better dataset to monitor the progressive actions of different erosion processes. Establishing chronologies of 3D models and schedules of events helps identifying sources of erosion. Concerned volumes can be estimated more precisely too. Furthermore, the participatory survey also favors frequent field observations (photos and comments), which can be very useful to analyze data. For example, on 20 th August 2018, local volunteers reported that six days before, a group of three persons dug three sits in the sand cliff to watch a firework. Those sits were still visible in the field on 20 th August 2018 (Figure 3a). In November of the same year, those excavations had already provoked the collapse of the overlying sand and vegetation (dark blue in the upper right corner of the model, repaired by an "a" on Figure 5a and Figure 6), which refilled the anthropogenic holes (dark red area just below). On the same model, another typical "top blue/down red" couple is observed (b, on the left side of the model), illustrating a second gravity collapse. However, confrontation of the textured reference model and unprocessed photographs produced in August (Figure 3a) shows that screes and collapsed sand were already present in this area, suggesting that this part of the site had already started collapsing. The other successive models attest that this isolated collapse did not amplify over time, on the contrary of the first one, which tend to extend again between June and November 2019. This last month, a new collapse appears a few meters leftward from the first one (ε in Figure 5d and Figure 6). The model of -26 December 2019records an acceleration of collapsing, involving several linear meters (ε' in Figure 5e). On the model of 7 March 2020, a first phase of dispersion of the tumbled down material is observed, while on 7 April 2020some new material dropped down again, suggesting the simultaneous continuation of the collapse phenomenon. Here, the comparison of the reference model and the last produced model indicates that about 2.5 m 3 have dropped down over the 20 months survey. The high-resolution participatory survey adds crucial details like 1) human activities are involved in the destabilization of the right part of the major collapse, 2) the destabilization of the left part started in November 2019, drastically increased in December and was still active in April 2020, 3) the material collapsing is essentially composed of stones from the upper building and 4) the material collapsed is sometimes removed, probably by the sea. The additional confrontation of the schedule of local storms and the evolution of the morphology of the site revealed that storms are clearly involved in the massive collapse mechanism, but waves are not the major erosion source. Indeed, major storms are generally associated to major erosion pulses but erosion is generally recorded in the upper part of the site, never reached by waves, suggesting that on this site, wind, precipitations and soil water content were more involved than wave action in the erosion over this survey of 20 months. The fact that only minor gravity collapses occurred during the late spring storm Miguel supports this assumption because the climax of the storm occurred at low tide, with a tide coefficient of 85. Thus minor collapses were probably only reactivated by associated precipitations. On 22 December 2019, the storm Fabien was responsible of major collapses but the storm is associated to a small tide coefficient of 61, and precipitations are most probably responsible of the collapse since waves did not reach the site. Storms Ciara and Denis occurred during February spring tide but they seem more associated to dispersion of the material previously collapsed than to a major new collapsing event.

This test-monitoring is a very demonstrative example to illustrate the effectiveness of the participatory 3D SfM-S monitoring to discriminate different sources of erosion on a site (human, animals, wind, precipitations, waves, etc.) and thus to be able to establish appropriate protection strategies. Hence, during those 20 months, settling hard wave protections (rocks or concrete blocks) in front of the eroding area (as recommended by many residents) would probably have created additional wave dynamics at the base of the cliff (wave reflection, vortices, etc.) and provoked more damages than not to protect. On the contrary, preventing human accessibility to both feet and edge of the dune cliff seems urgent for the safety of all, including the site itself. The future of the building remains at the top of the site also requires a special attention to establish a management policy (make archaeological excavations and let it slowly fall down and disappear or find a way to protect it, but for how long?). The temporal irregularity of the survey shown in this example will be improved with the imminent implement of the SENTINELLES de la côte application. The involvement of dozens of local actors, and the possibility for them to report any observation in the field through the application, will allow the regular processing of a new SfM-S model per month. Unused datasets transmitted will be stored, allowing one to reconstruct other intercalated models if required, for instance to document erosion more precisely around a storm, a major gravity collapse or any other major event.

Conclusions

In 2018, the team of the participatory science project ODySéYeu codesigned a list of requirements in order to implement a high resolution/high frequency "participatory monitoring" of the erosion, in 3D, for nine sites along the coast of Yeu (Vendée, France).

Tests presented here highlight the ability of the SELPhCoAST workflow-an integrated solution proposed by the partner company DIGISCAN3D-to produce complete and reliable 3D surface models of the test site, based on photo datasets. Produced models are accurate enough (more than 95% of points closer than 5 cm to a professional TLS model) to allow detecting any decametric change of the monitored coastline portion. Minimizing the required number of photos, and offering very simple guidelines in the field, the workflow also optimizes field acquisitions and data transmission, enabling inexperienced operators (including children) to participate, with their own smart devices, which is congruent with initial requirements.

Using this solution for a high frequency/high resolution participatory monitoring allows decrypting erosion/accretion dynamics and sources on numerous sites, better than a low temporal resolution professional scanning.

Associated with the application SENTINELLES de la Côte, this integrated solution will soon provide citizens the possibility to become true sentinels of their own coasts and to report in-situ observations. Moreover, like scientists or decision-makers, participating citizens will get a direct access to monitoring data and field information, monthly updated site-per-site. This should facilitate the dialog between all actors and strengthen the local protection policy by increasing its credibility. Although this solution was specifically designed for the island of Yeu, it could be adapted to many other sites, contexts (mountain, heritage, etc.) and purposes (monitoring, valorization, dialog between actors, etc.).

Patents

The intellectual property of SELPhCoAST belongs to the DIGISCAN3D company, which registered an Enveloppe Soleau (DSO2020021130) at the INPI (French national institute for industrial property) in December 2020.

Figure 1 .

 1 Figure 1. (a-b) Localization of monitored sites and a few examples (c-f).

Figure 2 .

 2 Figure 2. Map of requirements for a 3D participatory monitoring tool, as established by the ODy-SéYeu consortium.

Figure 3 .

 3 Figure 3. First participatory test, 20 August 2018. (a) Textured "Structure from Motion" by Smart devices photography (SfM-S) mesh obtained with a Samsung Galaxy S7 and different points of interest, which will be indicated and documented on public models in Sketchfab®. (b) Position of inert zones considered to compare SfM-S and TLS models reconstructed on 20 August 2018. On the right side of the model, the histograms of distances between inert parts of SfM-S models and identical patches on the reference TLS model were plotted against the colored scale bar. Corresponding values of mean distance to the reference and standard deviation are given for each model in sketches 3 to 7. (c-g) For each smartphone model: spatial distribution of the difference between the SfM-S mesh and the reference TLS mesh. On the right side of each model, the histogram of distances between entire models was plotted against the colored scale bar.

Figure 4 .

 4 Figure 4. Spatial distribution of distances between the last SfM-S model and the simultaneous final TLS acquisition of 7 April 2020. On inert parts of models, the standard deviation significantly decreased with regards to results obtained with the same smartphone model in 2018 (previous figure).For a rather similar SfM-S model reconstructed, the required number of photographs droped from 54 to 33, and data acquisition was lower than 5 minutes, showing that after 20 months of semiparticipatory monitoring experience on the site, the improvements made in SELPhCoAST induced a significant gain in both accuracy and operability.

Figure 5 .

 5 Figure 5. (a-h) sketches represent the reference TLS mesh of 20 August 2018 on which displayed colors indicate the local difference (distance, in mm) between the reference mesh, and the new 3D model reconstructed after each survey (SfM-S or TLS), over the 20 months monitoring. The scale bar presented in (a) is common to all sketches. White Greek letters are mentioned in the text, and refer to events represented on the timescale in Figure 6.

Figure 6 .

 6 Figure 6. Timeline reconstructed combining field observations, reconstructed models and major meteorological events.

Table 1 .

 1 List of acronyms used in the text.

	Acronyms

Table 2 .

 2 Characteristics of various models of smartphone cameras used in this study. Green fields indicate smartphone models for which a 3D model was reconstructed with SELPhCoAST after one of the field tests, and met all the expectations of the ODySéYeu consortium. Orange fields point to models for which minor anomalies were observed on 3D models reconstructed. Red fields highlight configurations incompatible with the reconstruction of a viable 3D model.

	Smartphone Model	Use in this Study	Rear Camera Specifications	Image Size Produced During The Operation (Pixels)	35 Mm Equivalent Focal Length (Mm)	Is a 3d Model Reconstructed?	Is the Model Compatible with Accuracy Requirements?
	Huawei ® P20 Pro	Test 20/08/17 Regular monitoring	40 MPix + 10 MPix	4160 × 2336 (=10 Mpix) 3648 × 2736	27 27	Yes Yes	Yes (see text) Yes
		Test 20/08/17
	Samsung ® S7	Regular	12 MPix	4032 × 3024	26	Yes	Yes
		monitoring
	Samsung ® A3 Test 20/08/18	8 Mpix	4128 × 2322	27	Yes	Yes
	Apple ® iPhone X	Test 20/08/18	12 Mpix	4032 × 3024	28	Yes	Yes
	Sony ® Xperia XA1	Test 20/08/18	23 Mpix	3840 × 2160 (=8 Mpix)	27	Yes	Yes (see text)
	Samsung A10	Test 05/10/19	13 Mpix	4128 × 3096	27	Yes	Yes
	Samsung ® J3	Test 05/10/19	8 Mpix	2048 × 1152 (= 2.3 Mpix)	26	Yes	No

Acknowledgments: Additionally to funders, the authors wish to thank all volunteer operators for their active support in this project.

Data Availability Statement:

The data presented in this study are available on request from the corresponding authors. Native files are not publicly available due to their weight. Updated data, specifically designed for the web, can be visualized on Sketchfab (@ODySeYeu account), for each monitored site.

Funding: This research was funded by the municipality of Yeu, the Fondation de France, grant number 00105360; the Foundation de l'Université de Nantes; the regional council of Pays de la Loire, grant number 2019_14270; the departmental council of Vendée, grant number 2019/RDM00001 and the Agence de lʹEnvironnement et de la Maîtrise de lʹEnergie (ADEME), grant number 19ESC0003. The APC was funded by the Foundation de l'Université de Nantes.

Conflicts of Interest:

The authors declare no conflict of interest.


Associate Professor Eve Gardien

Between normality and disability: sensitive cognitive boundaries

Keywords: Disability, Diversity, Cognition, Normality, Intersubjectivity, Peerjectivity

, this article proposes to explore the effects of normality and of norms, accepted as reality/truth, on people who are experiencing rare situations. First, we will analyze the practical consequences of these norms on the use of the body and the physical environment. Then, based on the sociology of knowledge of everyday life, we will explain the partial lack of semanticization (Gardien, 2008) of the reality lived by people in rare situations. These analyses will highlight the major role of generally accepted criteria of relevance, and of the poorly recognized perceptual and cognitive boundaries that result from them. The conclusion will lead to courses of action aimed at broadening the field of intersubjectivity to include greater cognitive diversity.

Introduction

Observations made by Disability Studies [START_REF] Campbell | Disability Politics -Understanding our past, changing our future[END_REF] and many other non-academic activist movements have highlighted a lack of accessibility in the most ordinary living environments and the disabling barriers [START_REF] Fougeyrollas | La funambule, le fil et la toile. Transformations réciproques du sens du handicap[END_REF] limiting or preventing the action of some people considered as disabled. This has made it possible to move away from an individual-centered understanding of disability and to focus instead on the role played by the environment. This new perspective has contributed to advancements, notably at the political level, with accessibility standards being required for buildings, establishments open to the public, public transportation, the Internet, etc., or at the theoretical level with the concepts of universal design (Mace, 1998;[START_REF] Case | Universal Design, policy report[END_REF] and inclusion [START_REF] Young | Democraty and Inclusion[END_REF], noticeably enlarging the category of the able through a priori adjustments to the environment.

Critical Disability Studies reopen the debate on disability, examining hitherto commonly accepted distinctions between the biological and the social, impairment and disability. They shed light on the unquestioned normativity applied to concepts of normality and disability and on their social production. They create the concept of ableism to describe a social process that assigns people with different potential to the status of incapacitated or deficient [START_REF] Campbell | Contours of Ableism -The production of Disability and Abledness[END_REF][START_REF] Goodley | Dis/ability Studies -Theorising disablism and ableism[END_REF][START_REF] Tabin | Repenser la normalité : perspectives critiques sur le handicap, Lormont, Editions Le Bord de l'eau Vigarello G. & Vivès J[END_REF].

The world has been adapted by humans for humans over a few thousand years, if not many more. Forests are now crisscrossed with hiking trails, seashores are commonly developed for swimming or vacationing, the countryside is provided with paved roads, our cities with public transportation and miles of sidewalks, etc. In short, the world has been largely modified to accommodate certain types of potential bodies, generally referred to as functional bodies. There is nothing natural about this arrangement, even if it seems normal and obvious to most. It has been constructed materially and in an ideal manner over the centuries, following the process of the social construction of reality [START_REF] Berger | La construction sociale de la réalité, Paris, Armand Colin Borkman T[END_REF]. However, not only has the relationship to the material world been socially constructed; experience has also been semanticized (Gardien, 2008) and reciprocally typified (Schütz, 1962) in order to become intersubjective, and consequently shared and normal.

Within the framework of a cognitive sociology of everyday life (Schütz, 1962[START_REF] Berger | La construction sociale de la réalité, Paris, Armand Colin Borkman T[END_REF][START_REF] Zérubavel | Social Mindscapes -An invitation to Cognitive Sociology[END_REF], this article proposes to explore the effects of normality and of norms, accepted as reality/truth, on people experiencing rare situations. First, we will analyze the practical consequences of these norms on the use of the body and the physical environment. Then, based on the sociology of knowledge of everyday life, we will explain the partial lack of semanticization of the reality lived by people in rare situations. We will then develop some reflections on factors that contribute to the long-term perpetuation of these poorly recognized perceptual and cognitive boundaries. The conclusion will lead to proposed courses of action.

Practical consequences of a rare situation on the possibilities of acting in the world

The practical consequences of a rare situation are particularly difficult for individuals who suddenly find themselves in a body with new potential, following an accident, an illness, etc. In some cases, this even requires them to learn most of the activities of daily living at the expense of new effortsusually within the framework of rehabilitation -so that these actions become possible in new ways. An individual with low tetraplegia, having learned to brush their teeth 15 years earlier with an occupational therapist, explains this new socio-corporal arrangement in this way (Vigarello & Vivès, 1983):

First of all, to put the toothpaste on the bristles, it's necessary to put the toothbrush on the sink facing you, bristles towards the ceiling, and try to press the tube of toothpaste over the bristles. After several unsuccessful attempts (toothpaste stuck on the sink, or toothbrush rolling into the sink, etc.), partial victory is achieved by putting the toothbrush with its dose of toothpaste inside the oral cavity. Several attempts are generally necessary before success. That is to say approximately 30 mn/ brushing of teeth; at a rate of two brushings of teeth per day: one hour/day. (Summary of explanations from T., person with low tetraplegia, focus group, April 2013) This person was greatly surprised the day they observed an individual with approximately the same body potential as their own take a tube of toothpaste, bring it to their mouth and squeeze it, leaving toothpaste on their tongue, then grab the toothbrush, brush and rinse, the whole action lasting two or three minutes.

What can we understand from this example? Many of the body techniques learned in rehabilitation are based on a model of the way a so-called non-disabled body uses them. In other words, there is only one reference concerning the functioning of a healthy body, and it is biomedical. Rehabilitation therefore often, but not always, consists in bringing the new bodily potential as close as possible to the established norm, which implies thinking of it as an insufficiency and not simply as different.

"E: Yes, you have to brush your teeth with one hand, that's the way it is… […] They [ablebodied people and especially the care and rehabilitation professionals] don't see the purpose of the thing. The goal is to brush your teeth! After that, who cares if it's done with one or two hands?" (Excerpt from a focus group among people with disabilities, Paris, April 2013) More broadly, the internalization of social standards on the uses of the body generally allows each person to function well and effectively in the world. [START_REF] Mauss | Les techniques du corps[END_REF] highlights the traditional aspect of the transmission of the techniques of the body, society by society. However, these social norms, when taken as normality -as in the case of the biomedical model of the body -and not as a general example of bodily diversity, prevent or limit the exploration of bodily potentials for their own sake and for the sake of exploring and making discoveries about a new bodily potential.

Furthermore, the rehabilitated body does not systematically return to the functionality considered normal for the so-called non-disabled body. In the case of low tetraplegia, the use of technical aids to achieve a certain number of objectives by oneself is common (e.g., the wheelchair). However, these technical aids sometimes require the help of a third party to be installed before they can be used. Also, a technical aid does not always enable true functional independence, contrary to what its function suggests. Moreover, technical aids are usually designed to allow a particular act, just one. They are rarely multipurpose. This suggests that for each act one can no longer perform alone, a technical aid can be invented and manufactured. This implies in turn a large number of technical aids, and space to store them, but also choices that are sometimes difficult to make when leaving on a trip. Which ones are the most necessary? Finally, most technical aids are not everyday consumer goods. They are custom-made objects created in the context of rehabilitation. A damaged or lost technical aid cannot be easily replaced, an appointment with a rehabilitation specialist is required, and financing must be found.

Technical aids, because they are designed to allow an action or a posture similar to that of the socalled able-bodied body -in an approximation of what is considered the norm for the latter -are not often thought of in terms of design for everyday life. Their lack of versatility, their sometimes large size, their use requiring the intervention of human aids, etc., are partly explained by this.

We will not reexamine the lack of accessibility of the environment on a daily basis for some people. These facts -and the reflections on norms they elicit -are well known. It's thus at the level of the body and its uses, of objects and other extensions of the body in daily life, of environmental factors in the sense of the ICF (WHO, 2001) or of the MDH-PPH2 [START_REF] Fougeyrollas | La funambule, le fil et la toile. Transformations réciproques du sens du handicap[END_REF] that social -and biomedical -norms impose themselves and their effects. This is that rare situation in which the individual can't appreciate the good fortune of having a body that fits with ease into the world as it has been arranged by and for human beings for many centuries. Their daily life is not quite ordinary, for reasons linked to the interactions between their body and their environment, but not exclusively... Let's examine further the nature of everyday life, and its norms concerning perception and cognition.

Everyday life is based on normative cognitive socialization

For many of us, everyday life is characterized by the relative ease with which we relate to the world. Our daily experience seems to be self-evident. For example, when a person wakes up, they know what they are going to do with their day, or that they will not do anything with it. They know how to get to work, if that is in their schedule. They also know that they have other transportation options and what they are. They have an idea of their breakfast menu. They have done the shopping in anticipation of this moment, etc. A great deal of knowledge thus constructs our way of life, and our relationship to the world, to ourselves and to others. This knowledge is partly inscribed in our routines. It is part of our daily life, without us really being aware of its existence or its involvement in carrying out our projects and meeting our goals of the moment. How can we explain this fact?

Alfred Schütz (1962) shows that everyday life is based on a world shared with others (even though it's possible to become a hermit in a later stage of one's life). While the materiality of things imposes itself on each one of us from the outside (according to one's perceptive attributes), Schütz emphasizes that the meanings of beings and things also largely impose themselves on us from the outside. Indeed, the meanings of beings and things are not innate. They don't result from our genetic heritage or from our instincts. These meanings vary widely depending on the cultures and social environments a person frequents throughout their life. A child learns what reality is, and in particular the meanings to be attributed to the experiences he or she has during early socialization [START_REF] Berger | La construction sociale de la réalité, Paris, Armand Colin Borkman T[END_REF][START_REF] Berger | La construction sociale de la réalité, Paris, Armand Colin Borkman T[END_REF]: 177-188). Learning the meanings of the world contributes to the possibility of an intersubjectivity (Schütz, 1962) that allows sharing this world, communicating with others and acting in concert, and experiencing the feeling of partaking in the same reality, without this impeding the possibility of very personal and private experiences.

Building on Schütz's work, [START_REF] Berger | La construction sociale de la réalité, Paris, Armand Colin Borkman T[END_REF] highlight the importance of the social construction of reciprocal typifications and their transmission from generation to generation in the process of semanticization of the individual's experience of the world (Gardien, 2008). Thus, the understanding of the world, of oneself, and of others is achieved through the use of reciprocal typifications, such as the meanings and words present in the social environments one lives in. They are largely learned and internalized during childhood, but may be so at any age, in the context of secondary socialization [START_REF] Berger | La construction sociale de la réalité, Paris, Armand Colin Borkman T[END_REF][START_REF] Berger | La construction sociale de la réalité, Paris, Armand Colin Borkman T[END_REF]: 189-200). These typifications are models -simplifications of reality -that give one direction, making it possible to understand and to decide and act. This simplification of reality is not an individual or social choice, but a necessity arising from human limitations. Reality is too complex for the human cognitive potential to understand it all at once or in its entirety. For example, human beings are unable to detect ultraviolet light or ultrasound, among other things.

These reciprocal typifications, internalized by socialization, have major perceptual and cognitive consequences. For example, when individuals meet others for the first time, they cannot rely on knowledge acquired here or there to know who they are dealing with and how to behave. This is why, for this new situation, they will use typifications learned previously. In other words, they will employ the relevant distinctions to bear in mind according to their socialization, and probably without really thinking about it. Depending on the societies or social groups they live in, they will pay more or less attention to the fact of being children or adults, men or women, of belonging to this or that social group, of wearing this or that dress or using this or that vocabulary, etc. That said, whether or not individuals have specific a priori knowledge about a being or a thing, they nevertheless use typifications acquired beforehand to give meaning to their experience of the being or the thing. Knowing Juliette personally doesn't preclude an understanding of her also as a woman or as a former student of a renowned engineering school. Thus, a human being's experience of reality is based on -although not limited to -a "comprehensive and given reality confronting the individual in a manner analogous to the reality of the natural world." [START_REF] Berger | La construction sociale de la réalité, Paris, Armand Colin Borkman T[END_REF][START_REF] Berger | La construction sociale de la réalité, Paris, Armand Colin Borkman T[END_REF]: 85). Shared words and meanings -the internalized reciprocal typifications -constitute strong norms and normative expectations, including the establishment of social roles such as those of the able-bodied person and the disabled person. What happens then when the experience of reality is partially and persistently at odds with reciprocal typifications, with the intersubjectivity established as reality?

The partial absence of semanticization of the reality experienced by people in rare situations, and some of its effects Some people experience daily situations in which both the material world and social reality are not entirely adapted to their specific needs. Let's take the example of a person living in an electric wheelchair. In spite of commitments in public policies and the efforts of institutional actors to make society accessible, the fact remains that on a daily basis, many public spaces, or entire sections of roadways, or even the natural environment designed for winter sports, do not allow for mobility equivalent to that of people perceived as able-bodied.

As far as social reality is concerned, the same is generally true. What does this signify? The meanings available for understanding reality in different social environments are those useful for semanticizing the usual experiences of everyday life (Gardien, 2020). There are, of course, specificities in knowledge stocks [START_REF] Berger | La construction sociale de la réalité, Paris, Armand Colin Borkman T[END_REF] that are available depending on the social milieu. The daily experience of mathematics teachers does not involve exactly the same typifications as those of webmasters, even if parts of their daily life are similar. For a person experiencing an exceptional situation -for example with a spinal cord injury and living in a wheelchair -whether they are a mathematics teacher or a webmaster, they will not have the words and meanings at their disposal concerning sensations experienced below the lesion in their injured body [START_REF] Brunelles | Ergothérapeutes et relations thérapeutiques[END_REF]Gardien, 2008). The vocabulary is not found in any dictionaries.

These are very commonly experienced phenomena1 . Whether they have a biological, psychological or other cause, they have not been given meanings, much less typified reciprocally. Therefore, they don't contribute to a socially constructed reality or to intersubjectivity. This doesn't imply their nonexistence or the impossibility of experiencing them. Conversely, an important consequence of this non-semanticization of these phenomena is the absence of meanings in order to recognize them, to observe them, to distinguish them, to think about them, to understand them and to be able to act intentionally on them or their effects. Individuals living with these rare situations -in this precise case, the interaction between rare perceptions and the absence of available categories of thinking within social milieus -are thus helpless when faced with certain segments of their lived experience. This lack of shared and available words, meanings, and typifications makes it difficult to communicate with people who are not living the experience, including care and rehabilitation professionals who are usually considered knowledgeable on the issue (Goffman, 1963). Some people with spinal cord injuries (for example) nevertheless attempt to continue relying on their sensory experience. This often makes their words inaudible, unintelligible, or of no possible use to their listener.

In the physiotherapy room, a spinal cord injured patient is tested for the sensitivity of his body below the lesion. He tries to answer as precisely as possible to his rehabilitator: Faced with considerable difficulties in describing certain parts of their experience, or faced with a lack of agreement between perceptions coming from the sublesional part of the body and information gleaned from another source (vision, for example), very many people with spinal cord injuries give up semanticizing their experience. They feel they are dealing with sensory phenomena that are incoherent, random and therefore incomprehensible, or even with a sublesional part of their body that has a life of its own. A patient, lying on a rehabilitation table, talks with a third party while his physiotherapist moves his leg. While speaking to this third party, the patient states, among other things, that the physiotherapist is moving his right leg. His physiotherapist points out that he is moving the left leg. The patient is then very disconcerted -even disturbed -to discover his error, to note that he can experience sensations that do not correspond to the commonly accepted description of the situation in progress, nor even to the description he himself would have made by using his other senses. (Excerpt from Gardien, 2008: 176) Social factors also contribute to the reluctance of many injured people to semanticize their bodily experience. They fear being classified as somaticizing patients, or as hallucinating or having mental health problems, etc. The risk of a remark concerning some aspects of experience that challenges intersubjectivity being rebuffed -and the risk that the person who made it is stigmatized -are indeed not negligible… As [START_REF] Zérubavel | The fine line -Making distinctions in everyday life[END_REF] explains, the cognitive socialization of each individual promotes learning the fine line, this subtle line of demarcation that allows differentiating in a relevant way between what is recognized as existing or not, unimportant or not, between what should be ignored or not, etc. By learning these distinctions operating at the heart of everyday life, society applies a certain logic but also its norms, therefore making possible a sufficiently shared way of perceiving and understanding reality. It thus portrays the respective camps of the normal and the deviant, this time in relation to cognitive socialization [START_REF] Zérubavel | Social Mindscapes -An invitation to Cognitive Sociology[END_REF].

However, some phenomena can be observed and reproduced, and even be very significant due to their reliable efficacy for the body and their important functional relevance. The ability of some spinal cord injured people to use their contractures to perform movements that are otherwise impossible is now widely recognized in the field of physical medicine and rehabilitation. Their skills in chair-to-car transfers are also commonly used in rehabilitation centers by professionals to encourage other spinal cord injured people in their learning process.

The cognitive socialization of individuals enables each society to draw the boundaries between what exists and what does not exist

, what is red, blue and yellow, etc., and to stamp its fine lines on individuals, their perceptions and their cognition. However, some individuals in rare situations, for health reasons or not, experience sensations but also thoughts, gestures, and postures that deviate from the normative expectations of the surrounding intersubjectivity. They face daily perceptual and cognitive boundaries that distance them from so-called normal.

Going beyond these perceptual and cognitive boundaries: some thoughts A lack of reciprocal typifications in some cases, difficulty in typifying in other cases -and probably other causes as well -explain the lack of formalization or even the low level of creation of this rare experiential knowledge. In addition, many obstacles limit the transmission of this rare experiential knowledge: it doesn't fit criteria for the production of scientific knowledge, it has only nonsystematic compatibility with professional knowledge, it has little recognition and legitimacy in general (Borkman, 1976;[START_REF] Chamberlain | On our Own -Patient-controlled Alternatives to the Mental Health System[END_REF]Godrie and Dos Santos, 2017;Gardien, 2017), it is often overlooked even by those who possess it, it is usually informal in nature, it has limited social distribution, and there is often denial of the possibility that an alternative social construction of reality can exist (Gardien, 2017).

Another explanatory factor also deserves further investigation: general structures of relevance [START_REF] Berger | La construction sociale de la réalité, Paris, Armand Colin Borkman T[END_REF]. As [START_REF] Zérubavel | Social Mindscapes -An invitation to Cognitive Sociology[END_REF] notes, our contemporary world grants relevance and legitimacy primarily to cognitive individualism [START_REF] Downes | Socializing Naturalized Philosophy of Sciences[END_REF] largely driven by the intersubjectivity of individuals, at least those sharing Western reality. It also subscribes to a cognitive universalism based on Kantian rationalism (1990 [1781]) that examines the frameworks of human understanding and is widely used in the field of cognitive sciences. Two legitimate conceptions of our understanding thus coexist: that of the thinker facing the world alone and that of a cognitive potential specific to the human species.

These two concepts both focus on reason, thus following a tradition of thought espoused by Descartes (1637). This dominance of reason neglects lived experience. Without repeating the extensive debates between empiricists and rationalists, it's clear that rationality cannot be exercised without the capacity to discern, define, etc.; all activities that are possible thanks to language. But the latter is a product of the social construction of reality, of the socially constructed relationship with experience. Thus, it's not possible to reason without experience, which doesn't mean that the method of systematic doubt concerning one's own experience is not useful and relevant. But the "I" and the action of "thinking" stated by Descartes shows that his cogito ergo sum is based on socially constructed categories existing prior to his reasoning, making it possible to distinguish the fine line [START_REF] Zérubavel | The fine line -Making distinctions in everyday life[END_REF] between, for instance, his "I" and what is not "I". The "I" is in fact partly the result of a social learning process that presupposes prior semanticization of the experience of a self on the basis of words and meanings available in the social environments one lives in (Gardien, 2008). The object of human rationality always involves an experience essentially mediated by language. For these reasons at least, we disagree with the usually accepted separation between rationality and experience. [START_REF] Zérubavel | Social Mindscapes -An invitation to Cognitive Sociology[END_REF] contributes another element to our thinking on the general structures of relevance. He shows that between cognitive individualism and cognitive universalism, there is a lack of a cognitive sociology to study the differences observed between social groups and the cognitive diversity that is socially constituted and distributed. In other words, he introduces a new explanatory factor that goes beyond the simple individual/human universal continuum -cognitive socializationand that is based largely on the transmission of reciprocal typifications of the experience of reality from one generation to the next [START_REF] Berger | La construction sociale de la réalité, Paris, Armand Colin Borkman T[END_REF]. However, this important advance does not explain whole areas of lived experience that are not semanticized, and the significant consequences of this for those directly concerned.

According to our present state of knowledge, these areas of experience that are not reciprocally typified are the result of socialized individuals living rare experiences. They are not differences between social groups or societies. These rare experiences concern individuals and not groups, and the semanticization and typification of the experience often remains the work of a single individual or of a few persons, if they are in contact with their peers. These individuals find themselves faced with the immense task of typifying their experiences by themselves, without any real reference points or method, and generally without any support. Thus, the advances in cognitive sociology proposed by Zérubavel concerning the cognition of groups or societies are not sufficient to solve the problem of the reciprocal typification of rare experiences.

There is consequently a need to establish an epistemology specific to cognitive sociology, no longer dedicated to cognitive distinctions between social groups or societies, but knowledge resulting from experiences of rare situations lived by socialized individuals. This cognitive sociology would examine the social processes underlying everyday situations considered as normal and reciprocally typified, and those rare situations -not ordinary and not well semanticized -that are not reciprocally typified.

One aspect of the general structures of relevance interferes with the semanticization and reciprocal typification of these rare experiences. This experiential knowledge is a priori illegitimate because of its subjectivity. This knowledge would only be valid for one individual, the one living the rare experience. Is this assessment pertinent?

The characteristics of this knowledge are not those of the material objectivity of nature, nor of the legitimacy of social intersubjectivity. However, these semanticizations of rare experiences by one or a few individuals show important similarities between people who don't know each other. For example, knowledge generated by people living in wheelchairs concerning the use of buses commonly includes a focus on positioning oneself in the bus shelter in order to be seen by the driver and to obtain the descent of the ramp, and a focus when entering a crowded bus on the firm negotiation of one's place that is already occupied by one or two baby strollers, etc. This is knowledge that an ostensibly able-bodied person never develops. This is knowledge that displays frank similarities between individuals who have never met. This experiential knowledge is therefore not subjective: it is valid for all peers and not simply for this or that individual. It doesn't derive from individual preferences or habits and is independent of the will of this or that individual. However, this experiential knowledge is not objective in the sense of being valid for all persons. This knowledge is peerjective (Gardien, 2020): valid for all people living similar rare situations. These situations have been semanticized and typified by individuals, but the social conditions of their production have not enabled the creation and legitimization of an intersubjectivity confined to peers.

Conclusion

Examining the question of norms and normality from the perspective of ableism implies not only questioning social normativity and its corollary effects of stigmatization, discrimination, exclusion, inferiorization, infantilization, etc. Another analytical line of inquiry is suggested by [START_REF] Bourdieu | Méditations pascaliennes[END_REF] remark on those norms that no longer need to be stated in order to be thought about and applied, because they are the doxa.

Theoretically deconstructing the self-evident concepts of disability or impairment can involve analyzing the processes of social cognition. Indeed, as [START_REF] Berger | La construction sociale de la réalité, Paris, Armand Colin Borkman T[END_REF] point out, once socially attributed meanings of reality have become widely shared reciprocal typifications, once they have been transmitted, learned and internalized by the following generations, they become obvious, they become the socially shared reality. Considered valid for everyone, this intersubjectivity is considered to be objective. During its transmission and learning, it is not presented as a social construction but as the truth: what is. This is why people feel constrained to deal with it as though it were as irrefutable as physical matter.

Once a particular intersubjectivity has become established, it becomes difficult for a group or a society to alternative semanticizations and typifications, notably because of the general structures of relevance. Hence the importance of questioning these structures of relevance: are they the only valid ones? Do they account for the diversity of lived experiences and rare situations, or do they standardize perceptions and cognitions? The view of this article answers this question: they normalize perceptions and cognitions.

Therefore, in order to allow cognitive diversity to be acknowledged and accepted by our societies, it is important to examine the foundations of general structures of relevance. Some avenues of research have been suggested: refusing to take for granted the opposition between rationality and experience; building a cognitive sociology that supplements cognitive individualism and universalism by studying social diversity and not just individual singularities or human transversalities; discarding the practice of sociological thinking in terms of groups and societies for an analysis in terms of knowledge derived from the experience of rare situations by socialized individuals. It is through the effort invested in discussing the presuppositions underlying normality and the normal relationship to reality, that cognitive diversity, and in particular peerjectivity (Guardian, 2020), can be constructed2 , adopted and become legitimate.

"

  Physiotherapist: Does that sting? Patient: No, not really… [Pause] Physiotherapist: Do you usually feel it? Patient: Not usually but I feel… [Pause] Physiotherapist: And there? Patient: I feel a little more…[Pause] Physiotherapist: Here? Patient: Less…." (Excerpt from Gardien, 2008: 169)

Phantom pains are a well-known example, but the range of these phenomena is much wider, and few are recognized and investigated.

This type of experiential knowledge cannot be produced by monitoring the practices of everyday life, for reasons that are beyond the scope of this paper. The "survey" proposed by John Dewey will certainly not be sufficient, although of some use. A specific methodology dedicated to the production of peerjective knowledge should be set up on the basis of this continuing epistemological effort.

This work was funded by the Public Health Research Institut. "AAP 2019 -Handicap et perte d'autonomie -session 10" Réf. INSERM de la convention 20II003-00