Marie-Benoît Magrini

Hugo Fernandez-Inigo

Antoine Doré

Olivier Pauly

Marie-Benoit Magrini
email: marie-benoit.magrini@inrae.fr

How institutional food services can contribute to sustainable agrifood systems? Investigating legume serving, cooking and sourcing through France in 2019

Keywords: catering, sustainability transition, pulses, soya, plant protein, alternative dishes

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

Introduction

One main issue of sustainable diets is to promote eating habits that are good for both human and environmental health (FAO, 2012). This issue represents a great challenge for agrifood systems and new concepts have been developed such as "nutrition-sensitive agriculture" [START_REF] Jaenicke | Entry points into a nutrition-sensitive agriculture[END_REF], "ecological public health" [START_REF] Lang | Ecological public health: The 21st century's big idea? An essay by Tim Lang and Geof Rayner[END_REF] or "environmental nutrition" [START_REF] Sabaté | Environmental nutrition: Connecting health and nutrition with environmentally sustainable diets[END_REF]. Each one calls for a more integrative conception of food and agricultural systems [START_REF] Garnett | Where are the best opportunities for reducing greenhouse gas emissions in the food system (including the food chain)?[END_REF][START_REF] Hallström | Environmental impact of dietary change: A systematic review[END_REF][START_REF] Meynard | Designing coupled innovations for the sustainability transition of agrifood systems[END_REF].

Among the levers for a sustainability transition of agrifood systems, developing legumes presents both environmental and nutritional benefits. Legumes include soya and pulses (crops such as lentils, beans or chickpeas). Firstly, they mean a reduction in nitrogen fertilization through crop rotations thereby contributing to reducing greenhouse gas emissions (e.g. [START_REF] Peoples | Chapter 8-The Contributions of Legumes to Reducing the Environmental Risk of Agricultural Production[END_REF]. Secondly, they contribute towards improving nutrient balance particularly in fibers and proteins, especially in regard to issues on reducing animal-based protein consumption [START_REF] Hallström | Environmental impact of dietary change: A systematic review[END_REF][START_REF] Marlow | Comparing the water, energy, pesticide and fertilizer usage for the production of foods consumed by different dietary types in California[END_REF][START_REF] Vainio | From beef to beans: Eating motives and the replacement of animal proteins with plant proteins among Finnish consumers[END_REF]. Nevertheless, the re-launching of legumes in Western countries faces lock-ins, in both production and consumption, and particularly in Europe [START_REF] Magrini | Why are grain-legumes rarely present in cropping systems despite their environmental and nutritional benefits? Analyzing lock-in in the French agrifood system[END_REF][START_REF] Magrini | Pulses for Sustainability: Breaking Agriculture and Food Sectors Out of Lock-In[END_REF]. On the production front, the challenge is to promote sustainable farming systems that include more legumes with more diversity, without an increase in imports which are already high. On the consumption front, compared to major crops such as cereals, legume consumption is very low: 4,7 kg/year/person for pulses and 110 kg/year/person for wheat (Eurostats). Legumes require soaking and longer cooking times, are often associated with digestive problems (flatulence), have an old-fashioned image and are subject to "erroneous and limited mental representations" about how to cook them and associate them with other ingredients to create tasty and healthy dishes [START_REF] Melendrez-Ruiz | French consumers know the benefits of pulses, but do not choose them: An exploratory study combining indirect and direct approaches[END_REF]. In addition, there is a clear lack of innovative pulse-based foodstuffs [START_REF] Niva | Barriers to Increasing Plant Protein Consumption in Western Populations[END_REF][START_REF] Van Der Weele | Meat alternatives: An integrative comparison[END_REF]. Finding ways to increase legume consumption is difficult, as it is not easy to change eating habits. This paper investigates a specific sector considered as a great driver for agrifood sustainability transition: food services, also known as catering1 . Food services is an expanding sector, influencing eating habits and also impacting agrifood systems through their food supply chain organisations. Traditionally, catering is divided into two categories (Bourlakis and Weightman, 2003;[START_REF] Edwards | The foodservice industry: Eating out is more than just a meal[END_REF]: i) the "profit sector" that comprises profit-orientated establishments such as restaurants, fast-food chain outlets, cafes, takeaways, pubs, leisure and travel catering outlets; and ii) the "cost food services sector", which typically refers to non-profit catering activities for businesses, education and healthcare, often labelled as "Institutional Food Services" (IFS). The IFS sector is daily frequented by employees, pupils, students, patients and the elderly in workplaces, schools, universities, hospitals or retirement homes.

Our study focuses on the IFS sector, being deemed more likely to influence eating habits than the profit-oriented sector (as assumed by French public policies through, for instance, the obligation to introduce at least one vegetarian meal every week in school canteens since the 1 st November 2019). Hence, the objective of our study is to describe legume uses in IFS in order to identify brakes and levers for their promotion in IFS, particularly with regard to sustainable practices, such as their use in vegetarian dishes.

We focus on France where legume consumption is very low (2 kg/year/person, Graph'Agri, 2019) but which provides the highest number of meals served through the IFS sector in Europe (4 billion per year). We considered the two models dividing the IFS sector [START_REF] Stahlbrand | The Food For Life Catering Mark: Implementing the Sustainability Transition in University Food Procurement[END_REF][START_REF] Xerfi | La restauration collective[END_REF]:

the contracting-out model (40% of the IFS market in France and the largest in Europe) with around 1 000 private companies, under contract with institutions or companies that do not directly manage their own catering services ; and the self-managing model (60% of the French IFS market), where institutions or companies manage their own catering services2 .

Moreover, whilst several studies advance the idea that the IFS sector is a facilitator in promoting sustainable agrifood systems [START_REF] Edwards | The foodservice industry: Eating out is more than just a meal[END_REF][START_REF] Vainio | From beef to beans: Eating motives and the replacement of animal proteins with plant proteins among Finnish consumers[END_REF][START_REF] Graça | Reducing meat consumption and following plant-based diets: Current evidence and future directions to inform integrated transitions[END_REF][START_REF] Jones | Chapter 2-Trends in the Global Food System and Implications for Institutional Foodservice[END_REF], only some take into account both environmental and nutritional issues. Most studies deal either with questions of waste reduction (e.g. [START_REF] Derqui | Towards more sustainable food systems. Addressing food waste at school canteens[END_REF][START_REF] Martin-Rios | Food waste management innovations in the foodservice industry[END_REF], food safety (e.g. De [START_REF] De Boeck | Method triangulation to assess different aspects of food safety culture in food service operations[END_REF], nutritional and dietary standards in meals (e.g., [START_REF] Vieux | Dietary Standards for School Catering in France: Serving Moderate Quantities to Improve Dietary Quality Without Increasing the Food-related Cost of Meals[END_REF][START_REF] Vieux | Nutritional Quality of School Meals in France: Impact of Guidelines and the Role of Protein Dishes[END_REF], health (e.g. [START_REF] Decataldo | Is eating in the school canteen better to fight overweight? A sociological observational study on nutrition in Italian children[END_REF], or local supplying [START_REF] Stahlbrand | The Food For Life Catering Mark: Implementing the Sustainability Transition in University Food Procurement[END_REF][START_REF] Orlando | The role of public mass catering in local foodshed governance toward self-reliance of Metropolitan regions[END_REF]. But none of them consider IFS sustainability transition in a more integrative way. To do so, we built a socio-technical analytical framework on three main dimensions: i) frequency and diversity of legumes served; ii) cooking methods and alternative dishes (vegetarian/vegan)3 with legumes; iii) legume sourcing through supply chain organisations and eco-labels.

We used several sources of information (open-ended interviews, literature and reports on the IFS sector) to build a wide survey addressed to IFS kitchens in France between April and August 2019 (i.e. before the experimental obligation to introduce vegetarian meals in school canteens). We selected 383 complete answers to describe kitchens' practices including legume uses. Through clustering methods, we identified heterogeneous profiles regarding legume uses and commitment to sustainability. This study provides original insights on the levers to develop legumes in a sustainable way, especially to support the development of vegetarian dishes.

Section 2 marks out the analytical framework. Section 3 explains the methodology we followed. Section 4 presents and discusses the results. Section 5 concludes.

A socio-technical analytical framework to analyse the drivers of legumes development in the IFS sector

Our integrative approach focuses on three main dimensions: legume-serving subject to consumer preferences and dietary guidelines (2.1), legume-cooking methods along with technical and food safety constraints (2.2) and legume-sourcing through supply chains (2.3).

Serving legumes: a trade-off between consumer preferences and dietary guidelines

Consumption is influenced by the intake of recommended daily nutrients diffused by public authorities and used by caterers. There has been no specific promotion in the past concerning legume consumption. But since 2019, French public dietary guidelines on pulses consumption have changed, arguing we should "eat pulses at least twice a week". Yet nutritional rules are recommendations and not in any way compulsory except for schools for which caterers must respect certain nutritional rules4 . Therefore, caterers can be proactive or not in promoting sustainable diets with more legumes. Moreover, canteens adapt their meals to their guests' characteristics and expectations. [START_REF] Tsui | How cooks navigate nutrition, hunger and care in public-sector foodservice settings[END_REF] argued that cooks (or kitchen supervisors) are central actors in the management of all these dimensions that impact the composition of meals; they underlined that, beyond dietary guidelines, cooks take into account consumers' varying preferences in order to maximise "food consumption and enjoyment". Which means that if consumers themselves do not recognise the values in eating legumes, cooks will lack motivation in proposing legumes on a regular basis; and also, cooks' skills will be determinant in managing to produce tasty-enough meals with legumes to increase legume popularity. Eating legumes, is often linked to animal-based consumption reduction in literature (e.g. [START_REF] Van Der Weele | Meat alternatives: An integrative comparison[END_REF][START_REF] Niva | Barriers to Increasing Plant Protein Consumption in Western Populations[END_REF] as well as in NGOs reports (e.g., WWF, 2017;[START_REF] Poux | An agroecological Europe in 2050: Multifunctional agriculture for healthy eating[END_REF]. Recent studies show that vegetarians consume more legumes for their richness in protein [START_REF] Figueira | Consumer Understanding and Culinary Use of Legumes in Australia[END_REF] and that, in general, consumers associate pulses with a vegetarian diet [START_REF] Melendrez-Ruiz | French consumers know the benefits of pulses, but do not choose them: An exploratory study combining indirect and direct approaches[END_REF]. Health also influences eating habits: for instance, diabetics could consume more pulses to help control blood sugar levels. Environmental awareness influences consumption as well: consumers of organic products consume more legumes that the average population [START_REF] Solagro | Le revers de notre assiette[END_REF]. In France, 34% of consumers declare to be flexitarian5 , which could lead to an increase in legume consumption.

Cooking legumes: cooks' skills, technical and food safety constraints

Most pulses suffer from certain cooking disadvantages. They require soaking and take longer to cook. Also, certain consumers encounter residual digestibility problems even after correct soaking times. However specific cooking recipes such as adding spices and adopting precise cooking times could solve this issue. Kitchens' abilities to serve more legumes will then depend on the cooks' skills in preparing appetising legume-based meals, notably in adding legumes to alternative dishes aimed at reducing meat consumption [START_REF] Graça | Reducing meat consumption and following plant-based diets: Current evidence and future directions to inform integrated transitions[END_REF].

Another type of constraint could be linked to the organisation of the cooking chain. Two models of catering services differ from each other in regards to where the foods are prepared and delivered [START_REF] Fusi | Evaluation of environmental impacts in the catering sector: The case of pasta[END_REF]: the "deferred system" (central kitchens send out prepared dishes or preprocessed ingredients/meals to satellite sites) and the "cook-served system" (the meals are cooked and served on the same site). In the deferred system, the cook-warm chain can have an impact on the taste and quality of legume-based dishes, seeing as the time difference between preparation in the catering centre and consumption can be several hours or days, depending on the method used in preservation. Hence, various technical constraints could lead to different strategies in the choice of raw materials and dishes to be served with legumes. The various structures in which they are embedded also could allow us to tackle technological or logistic constraints in different ways.

Sourcing legumes: foodstuff categories and supply chains

Whilst the modern agrifood system tends to favour large purchase platforms (central purchasing, wholesalers), shorter supply chains and local distribution networks are currently becoming a trend; local supply chains are mostly defined within region borders as mentioned and adopted in the study of [START_REF] Orlando | The role of public mass catering in local foodshed governance toward self-reliance of Metropolitan regions[END_REF]. The EU strategy is targeted at promoting a re-organisation and relocalisation of the food system, that improves local economic sustainability and social cohesion. In France, local produce is increasingly a central purchase criterion for consumers [START_REF] Praly | Chapitre 8. Repenser l'échelle d'approvisionnement des cantines[END_REF]Le Velly and Brechet, 2011) and authorities (through "Territorial Food Plan", for instance), aimed to counteract the negative externalities of globalisation (e.g. dependence on foreign goods and international market prices, energy and GHG emissions due to transport, etc.).

Some actors consider the "creative procurement policy, which takes a holistic view of the food chain" as a strategic target to calibrating production and consumption on a local level (Morgan and Sonnino, 2007: 19). These strategies are strongly promoted based on IFS initiatives such as in the French city Mouans-Sarthoux where school IFS is under a self-managing model using 100% organic foodstuffs and mainly local food (Pérole et al., 2018).

Besides, French farmers (like all European farmers) face fierce international competition in regards to importation. In France, 70% of legume consumption is imported6 . But 40% of pulse production is organic7 since legumes are a main lever for the nitrogen cycle in crop rotation. Therefore, pulses could be a lever for increasing organic sourcing in IFS.

Finally, legumes present an advantage owing to easy storage, their consumption not being restricted to seasons. New industrial food products have been developed to facilitate the consumption of pulses such as ready-to-cook pulses; and some agrifood firms consider the IFS market as a target strategy for familiarising consumers with new products [START_REF] Lascialfari | The drivers of product innovations in pulse-based foods: Insights from case studies in France, Italy and USA[END_REF].

Synthesis

Based on those main dimensions that shape legume sourcing, cooking and serving practices in the IFS sector (Figure 1), our study is aimed at understanding those current practices of caterers.

Figure 1. Synthesis of the analytical framework on practices regarding legumes in the IFS sector

Research design

This research is based on a wide survey addressed to cooks and kitchen supervisors (3.1). Based on clustering methods we identified various profiles of caterers (3.2).

An original online survey addressed to IFS kitchens in France

First, based on web searching we identified the main actors of the IFS sector, notably professional associations that represent catering operators, who we contacted for open-ended interviews (see Table A1 in Supplementary Material). These interviews led to a better understanding of the various dimensions that influence caterer practices and helped us to build our survey.

Secondly, we addressed the survey to IFS kitchens (production sites) between April and August 2019, through Lime Survey online application. As underlined by [START_REF] Tsui | How cooks navigate nutrition, hunger and care in public-sector foodservice settings[END_REF], cooks (but also kitchen managers or purchasing and nutrition managers) are recognised to have a major role in the IFS sector, and we considered them as relevant information providers.

The survey (free available8 ) was organized through 10 sections:

1. Description of the production site (kitchen): cooked-served or deferred production system, self-managing or contracting-out models, localisation, quantity of meals served by segments (guests); 2. Serving practices regarding legumes: frequency, diversity, labels; 3. Sourcing and purchasing practices regarding legumes: legume-based products types, supply chain organisation, products' geographical origins, structure's policy on food sourcing; 4. Knowledge as regards nutritional intakes of legumes; 5. Legumes in alternative dishes; 6. Perceptions on guests' expectations regarding legumes; 7. Difficulties encountered with legumes; 8. Areas for improvement regarding legumes; 9. Kitchen's sustainable food programs; 10. Other general information: employees, price invoiced to the guest, menus elaboration, dietary guidelines, networks and partnerships.

The survey was tested with several operators previously interviewed and with four kitchen managers (of various kitchen types) not previously interviewed. The survey was diffused on a national scale through various channels: public authorities, volunteers we identified during the interviews, the newsletters of main IFS operators and through professional associations in the IFS sector. We obtained 568 usable responses of which 383 were complete.

Compared to data collected from professional reports, the representativeness of answers presents a small bias in regards to the two IFS models with a slight over-representation of self-managing models (Table A2 in Supplementary Material); and within contracting-out kitchens, an imbalance in the amount of responses for some main companies operating in the French IFS sector (Table A3 in Supplementary Material). As regards to the type of production model (deferred or on-site) and the size of the kitchens interviewed, we managed to get responses from a suitable diversity of sites; from small kitchens serving less than 80 meals per week to the biggest ones serving over 15,000 meals a week. Concerning segments, some PCCs are specialised in specific segments, especially in the cases of Healthcare and Childcare. Otherwise, most caterers operate with several segments.

Clustering methods for identifying caterers' profiles

The clustering process helped us identify caterers' profiles in regard to their practices with legumes.

It was carried out in three stages, by using the free FactoMineR package9 . We first launched different Multiple Correspondence Analysis (MCA), by varying the dataset from answers to the survey. This step highlighted the strong impact of missing data, leading to the elimination of 185 respondents (kitchens) who did not answer certain questions we selected for the analysis. Thus, 383 kitchens were selected and Table 1 presents the frequencies of the variables' modalities used for the clustering. An MCA was carried out on this population in order to obtain final numerical axes, which concentrate main statistical information (inertia) in the first ones. Secondly, from the 7 35 axes generated by this MCA, we selected the first 12 (56% of the total inertia) to perform a Hierarchical Cluster Analysis (HCA). HCA provides a classification by successive groupings. Table 2 presents the total by groups of the HCA dendrogram: after analysing different partitions, we decided to keep the 6-groups classification. Thirdly, we reinforced it with a K-means Cluster Analysis and Table 3 presents the correspondence matrix. The K-means clustering step increases variance between classes whilst reducing variance within classes (Table 4) to obtain our final 6groups classification.

Table 1. Modality frequencies of the variables used for clustering (n=383)

Var. name Definition Modalities Freq.

General characteristics

Number of guests

Guests served by the kitchen per week

High -more than 1,500 Medium -between 600 and 1499 Low -between 200 and 599 Very low -less than 199

Results and discussion

First, we present descriptive statistics on legume uses to have an overview of the current situation in French IFS (4.1). Then, we present the clustering that reveals major heterogeneity in IFS on the practices regarding legumes and commitments to sustainability (4.2). Those results lead to several insights in terms of policy implications (4.3).

Main trends in caterers' practices regarding legumes in France

Firstly, we observed a diversity in legume serving frequencies (Table 5).10 61% of caterers serve legumes less than twice a week, which is below current National dietary guidelines. Most of them serve only lunches 5 days a week, so legume serving frequencies do not seem high enough to encourage consumers to shift towards eating more legumes, seeing as private legume consumption is very low. However, 21% of caterers serve legumes over twice a week, and even some serve them every day (8%). On the whole, contracting-out kitchens serve legumes more frequently. This could be explained by the fact that they receive information more frequently via associations' newsletters who communicate on dietary guidelines. Furthermore, legume-serving frequencies are lower in the Education segment (66% serve legumes less than twice a week) compared to the Business segment (47% serve less than twice a week). The Healthcare segment presents the highest legume-serving frequency (38% serve legumes less than twice a week), probably due to a higher awareness of their nutritional interest by guests, and the fact that legumes are more common with the elderly.

Comparing contracting-out and self-managing services, the former present higher serving frequencies in Business and Healthcare, but equal frequencies in Education. As regards to the type of production, on-site kitchens present higher frequencies. Caterers who have been proposing alternative dishes for a longer time, also serve legumes more frequently: 35% of caterers who have been proposing alternative dishes for over 5 years serve legumes more than twice a week, while it is only 17% for the caterers who have been proposing alternative dishes for more than 2 years.

As explained in section 2, legume-serving results from a trade-off between giving enjoyment to guests and providing food with a sound nutritional profile. On one hand, most respondents estimate that legumes are not very popular among guests, particularly among children and teenagers. In the Education segment, only 12% of respondents consider that legumes are popular among guests; against 28% of the respondents in the Business segment, and 21% in the Healthcare segment. We also observe that low legume-popularity perceived by cooks is strongly correlated with low frequency serving. Those results confirm that, according to respondents, legumes are not very attractive to consumers. Nevertheless, the Business segment is more committed to serving legumes. Over 88% of all respondents consider that legumes contribute to healthier and more sustainable diets and 99% agree with the need to promote legumes as a main lever in favouring sustainability shifts among consumers. In addition, whilst digestive discomfort is often cited to explain low consumption of pulses, only 60% of respondents agree with this argument. Most of them recognise also their richness both in fibre and protein.

Legumes are unequally served in terms of species. Lentils are the most common (71% of respondents regularly serve lentils), followed by beans (57%), chickpeas (27%), soya (12%), split peas (10%); faba-beans come in last with only 4% of respondents serving them regularly. Another interesting result is that 55% of respondents declare to have never served faba-beans, 36% have never served soya, 34% have never served split peas and 9% have never served chickpeas. Therefore, there is a high diversity of practices according to species. Through a post-calculated score, based on the legumes served in the various dishes constituting a meal, we defined a legume diversity score (Table 1). There is a high amplitude of scores, differently correlated with the serving frequency, however seemingly more correlated with cooks' skills. Indeed, capabilities and skills are required to develop legumes in diets. We also observe that low popularity consideration is strongly correlated with the fact that cooks admit they encounter difficulties cooking legumes, whilst those declaring high popularity rates confirm not having difficulties in cooking them. As a result, we observe a division between respondents: one half consider that cooking legumes is difficult while the other half does not.

Overall, if most respondents consider legumes not popular among guests, 80% agree that legumes remain interesting and innovative products. 75% agree with the need to have more dried legumebased ingredients (such as flour or pasta) and also more variety in legume grains (88%), whilst only 33% request more pre-cooked legume products or dishes. Most respondents (92%) recognise that having more recipes at their disposal will help them, and emphasized the need of training (89%) in this respect. Besides, whilst legumes may represent a technical constraint that could be solved by using canned, vacuum packed or pre-cooked products or dishes, raw legumes remain the main type of product used and 80% of respondents declare they never use pre-prepared (or already cooked) legumes.

Developing alternative dishes should favour legumes because of their richness in proteins. But the survey reveals that alternative dishes development is quite recent: only 13% of the respondents have been serving them for more than 5 years, and 23% for more than 2 years. 40% have been doing so for less than two years, or are planning to. In the Business segment alternative dishes have existed for longer periods. 26% of the respondents systematically use legumes for alternative dishes, and 52% on a regular basis, mainly in association with cereals. Therefore, alternative dishes remain a major driver of legume development. Legumes can be a source of innovation and they become more common, even in components where they are usually absent in the IFS sector such as desserts with, for example, newly-developed recipes using chickpea cooking water, such as vegan chocolate mousse often quoted.

Finally, concerning supply chains, wholesaling or central purchasing remain the main types regularly used by 88% of the respondents (only 12% declared to never use this type of sourcing). Few caterers regularly use alternative supply chains such as direct purchasing from farmers (8%) or from agricultural cooperatives (7%). But nearly 42% of respondents declare direct purchasing from farmers is a priority action for the next few years; and for more than 76%, developing regional sourcing is also a priority. We also observe that on-site kitchens more frequently use regional or national sourcing than the deferred system. For more than 69% of the respondents, developing organic sourcing is also a priority for the coming years, given the fact that certain legumes served regularly are organic (20% of the respondents serving beans regularly served organic beans, 33% for lentils). But it is important to note that most caterers have never served organic legumes (62%).

Kitchen profiling based on their characteristics and practices with legumes

Based on selected variables from this survey (Table 1), we conducted a clusterisation defining 6 main profiles of kitchens as explained in Section 3. We reported the statistical significance of the variables used in the clusterisation showing that variables on legume uses and kitchen size are the most discriminant (Table A4 in Supplementary Material); the statistical significance of the modalities contributing to each cluster from K-means clustering (Table A5 Supplementary Material) and from which the profiles depicted are established.

Figure 2 synthesized the characteristics of each cluster through two main axes: the diversity of legumes served and the frequency of legumes served by week. The modalities described in each cluster are the ones having a p-value <10%, most of them being <1%. From these clusters we described six profiles of kitchens, showing that there is no unique link between the frequency of legume serving and the other variables considered. In particular, we observed various commitments towards the sustainability dimensions of diets discussed in section 2, and a clear result appears: the kitchens that develop most legumes (both in frequency and diversity) are also those with more sustainable profiles according to the variables considered (such as local and organic sourcing and alternative dishes development).

Profiles with low legume serving frequencies: P1, P4 & P5

P1 -The "trend-followers" concern mainly the biggest kitchens (serving over 1 500 meals a day, almost absent from the other clusters) and which are more often under contracting-out models. They serve various segments but more frequently the Childcare, Business and Healthcare segments. The childcare segment is the most frequent (72% of the class). Even though they are characterised by low legume-serving frequencies, they propose a diversity of legumes through various types of dishes. The low frequency in legumes could appear in opposition to the fact that these kitchens are frequently engaged in sustainable food programs and serve alternative dishes. Hence, they seem to follow consumption and societal trends but are not at the forefront, compared to those also presenting sustainable food programs and alternative dishes but also serving with a higher frequency and diversity of legumes (P2 -The innovators). The low legume serving frequency of P1 could be explained by their size, as providing large quantities could prove problematic (this point was also mentioned during interviews) especially to obtain organic pulses (explaining why they are rarely served in this cluster) or to obtain French origin. They do not favour products facilitating legume-use (such as vacuum-packed, frozen, ready-to-use, etc). Platform supply purchasing is more frequent in this cluster. Furthermore, cooks more frequently declare that legume-cooking is not easy: such judgements might be reinforced because of the large quantities of meals they need to provide.

P4 -

The "elementals" are characterised by elemental practices regarding legumes. They don't have innovative or differentiating practices regarding legumes. It concerns mainly on-site and selfmanaged kitchens in the Education segment (98% of the class) with low number of guests. With a low legume serving frequency, low diversity and low popularity, this profile however declares not having problems with legume-cooking, probably because they use less raw legumes. Regarding geographical origin, P4 relies on national sourcing. But it presents weak sustainable commitment: organic legumes are never used, neither direct-to-the-farm supply; the majority do not have a sustainable food program, neither serve alternative dishes.

P5 -

The "reluctants" are quite similar to P4, gathering mainly self-managed kitchens in the Education segment (93% of the class) with low number of guests, but with both kitchen types. Like P4, P5 presents weak sustainable commitment: organic legumes are never used, nor direct-to-thefarm supply, most of them do not have a sustainable food program, nor serve alternative dishes. However, P5 presents a lower diversity of legumes than P4 and relies less on raw legumes but, above all, presents difficulties in cooking legumes. In addition, P5 relies more on imports (EU and worldwide) than P4. All these indicators conducted us to qualify P5 as reluctant because they do not adopt any of the dimensions contributing to sustainable diets.

Profiles with high legume-serving frequencies: P2, P3 & P6

P2 -The "innovators" are more medium-sized kitchens, mainly self-managed. They serve various segments, but less frequently Healthcare or Childcare segments; therefore, this class concerns mainly Education (81%) and Business (21%). Like group P1, they have sustainable food programs, serve alternative dishes more frequently, but they take this further as they also show the highest serving legume-frequency and diversity. In addition, most cooks of this class declare legumes are easy to cook and popularity is high. Their origin is mostly regional. They also more frequently declare using short legume supply chains with farmers or storage organisations, and regularly serving organic legumes. They mainly use raw legumes and more frequently legume-based dried ingredients (flour, pepites -new product like semolina -, etc.) compared to the whole sample. Finally, only in this cluster (as for P3) the modality "price is not the first determinant of legume purchase" is significant.

P6 -

The "traditionals" concern mainly the smallest kitchens of the sample (less than 200 guests served per week) and are more frequently associated with the contracting-out model. They are the opposite to P2 (the innovators) as whilst this group presents high frequencies of legumes, diversity is low. Furthermore, most of these caterers do not follow sustainable food programs, nor serve alternative dishes. Most of them never use direct farming or storage organisation supply chains, and do not purchase organic legumes. Therefore, their commitment towards sustainability could be qualified as low. Their high frequency of legume-serving could be then explained by the kind of guests they serve: the Healthcare segment (that includes the elderly) is over-represented in this class (70%). This segment is generally linked to a higher recognition of the nutritional intake of legumes and the fact that the elderly are more used to these products compared to younger people, and used to a low diversity of legumes types and dishes.

P3 -

The "ease-first" concern medium-sized kitchens not predominantly associated with any types of kitchen models or management. The Business segment is very little served by this group otherwise this class gathers various segments. This profile seems to seek "easy catering" as in this group, the caterers regularly use canned, vacuum-packed, frozen or ready-to-cook legumes and very rarely raw legumes. Legume serving frequency is high with quite a lot of diversity and most cooks declare cooking legumes is easy. The main supply chain is central platforms. In this group, price is not the main determinant of legume purchasing, corresponding to the fact that the type of products frequently used are more expensive than raw legumes. They declare more frequently that the origin is not national, but most of them declare they follow a sustainable food program.

Hence, this clustering reveals significant heterogeneity in caterers' profiles concerning legume issues: some caterers are already strongly committed to developing sustainable practices with legumes and others are still far from implementing such practices. This result confirms the necessity to develop and implement new policies for promoting legumes in a sustainable way, and most of the IFS professional organisations we interviewed recognised that up until now, no specific action has been carried out.

Figure 2. Kitchen profiles on their characteristics and practices regarding legumes from the six clusters

Lecture: The modalities considered in the clustering are depicted in Table 1. Only the modalities which were statistically significant (pvalue < 0,10) in each of the 6 clusters are mentioned in the figure (P1 corresponds to Cluster 1, etc.) and

Policy implications

How can sustainable practices be scaled-up in the IFS sector? The various dimensions analysed provide several insights for policymakers in fostering sustainable diets that include legumes. In addition, these insights could lead to a new research agenda for further investigation of the reasons why the different models of caterers do not present the same propensity to use legumes and adopt sustainable practices.

Using more legumes for sustainability is a recent issue and has not yet benefited from any specific fostering public policies. The adoption of new dietary guidelines by French public authorities for legumes in 2019 has not yet been followed up by any specific promotion through the media or public communications. Hence, any caterer already committed to sustainable practices with legumes can be highlighted as examples by policymakers and stakeholders. Our study reveals that such operators exist, even though they are a minority: the innovators profile concerns 16% of our sample. But considering the characteristics of this profile (mainly middle-sized, self-managed and serving chiefly the Education and Business segments), we must take a closer look at the following points.

1. From the clustering, our results suggest that in the IFS sector, the kitchens most committed to sustainability are mainly self-managed, in other terms they that are not enclosed in large private catering companies (PCCs). As often advanced in sustainability transition studies, free thinking opens the way to greater creativity. But no previous study has been developed to assert this point in the IFS sector. Here, it would seem that the self-managing model allows more independence in particular for their supply chains, and could be more receptive to emergent trends. Even if PCCs (contracting-out model) promote sound practices -for instance, they are currently developing new recipes with legumes as mentioned during interviews -the most sustainable practices with legumes are already being developed by caterers from the self-managing model. On the other hand, on-site and deferred systems did not seem to be strongly opposed regarding legume practices, notwithstanding the fact that the most innovative profile is mainly composed of on-site kitchens.

2. Comparing the networks of the most innovative caterers, and their exchanges, we can thoroughly grasp the influences that lead to innovative behaviour. These different observations reinforce the idea that adopting sustainable practices is currently more likely to be linked to caterers' immediate surroundings and environment than their ties with professional organisations, as most kitchens declared having few or no interactions with professional organisations. Hence, their personal commitments and the ways they acquire skills, rather than hierarchical injunctions, could influence the adoption of sustainable practices. This opens up a new research agenda focusing on chefs and cooks, seen as key-actors of sustainability transition. This will give us a better understanding of their socio-demographic characteristics, know-how and work conditions, since generally speaking, not much is known about this profession.

3. The selection of supply chains turns out to be an adequate proxy of sustainability profiles. We observed a strong correlation between more legume uses and sustainable chains, such as direct sourcing with farmers. The innovators, with the highest rate of legume frequency and diversity, are definitely those more active in organic and regional supplying. Nevertheless, most of the caterers declared their will to develop regional and organic legume supplying. Therefore, public authorities could foster the re-organisation of the food system to achieve this objective. We also observed that legumes are greatly used in alternative dishes. Overall, these observations suggest that promoting sustainable programs for legumes in the IFS sector could be a step to go further with more extensive programs in food sustainability.

4. Kitchen-size appears to be a main determinant in adopting sustainable practices with legumes: medium-sized kitchens being the most innovative. This could reveal how technical or logistical issues can be resolved more easily in kitchens with higher capacities (economically and spatially) compared to smaller kitchens. On the other hand, the biggest kitchens encounter more difficulties in sourcing and cooking large quantities of legumes, leaving also less scope for organic and local supplying, whereas smaller kitchens seem more flexible by varying their supplying methods. The size variable should be explored further in order to understand if infrastructures and technical constraints are main obstacles to sustainable practices. Hence, it raises the following question: which size for IFS (number of guests served) should be fostered to improve the implementation of sustainable practices?

5.

Training and recipes appears more important than for ready-to-cook legumes. Indeed, legume popularity among guests (perceived by cooks) was closely related to serving frequencies and cooks' skills. Thereby, when cooks declare to have difficulties in cooking legume, we also observed lower frequency and less popularity, which could suggest their guests do not enjoy the way legumes are being cooked. Cooks' skills appear crucial since most of the respondents clearly request more recipes and training regarding legumes. In addition, the majority of respondents also mentioned a greater use of raw legumes (also confirmed through the open-ended interviews). Therefore, whereas ready-to-cook or other pre-processed legumes could be a lever to make using legumes easier, this is not a preferable lever in IFS.

6. Any sustainable food policy in the IFS sector must take into account both cooks and guests. Most respondents (97%) mentioned that developing legumes in the IFS sector requires specific policies aimed at increasing consumer (guest) recognition of the benefits of eating legumes. This is in line with the suggestion of Vaino et al. ( 2016), in terms of public policies, to develop "consumers' culturally accepted ideas of healthy and 'natural' foods". In particular, as our survey reveals that legumes are less served in Education segment and taking into account that food habits are strongly related to childhood and teenage years, it appears crucial that public policies should start implementing the promotion of legumes in this segment. The innovators profile revealed that some caterers already serve more legumes with higher diversity for this segment. Additional studies could focus on the guests themselves served by those innovator caterers in order to understand how food choices follow to the home front, but also how guests could influence caterers' choices through social interactions.

Conclusion

Legumes are highlighted as an important lever for more sustainable and healthy diets, and IFS services impact agrifood systems by serving millions of people every day. However, we know very little about the practices of caterers, and nothing at all when it comes to legumes. This first-time study for France contributes towards filling this knowledge gap. In addition, it highlights various commitments to sustainability revealed through specific practices such as local and organic supply or alternative dishes development. We observed that the caterers highly committed to sustainability are few but could be a driving force for the sustainability transition; and further studies focusing on guests to understand how those food choices in IFS spread to the home front are required. This study calls also for comparative studies in Europe. Our framework provides an effective and productive starting point for investigating such issues through the case of legumes, and this framework could be adapted to any other food category. [START_REF] Xerfi | La restauration collective[END_REF]Perret et al., 2017). For our study, we considered the following ones: Education (primary, secondary and high schools, and higher education), Business and Administration (private companies and public institutions), Healthcare and Eldercare (hospitals, clinics, and retirement homes), Childcare centres (pre-schools). We collected only two answers for Defence and Penitentiary (army, police, prisons) segment, that were not considered in our analysis. Lecture: "Clu/Mod" corresponds to the percentage of the respondents from the sample having the modality that belong to the cluster; while "Mod/Clu" corresponds to the percentage of respondents in the cluster having the modality considered. "v.test" and its "p.value" correspond to the statistical test comparing the value of "Mod/Clu" and the one for the whole sample: a positive and statistically

Table 2 . Successive groupings from the Hierarchical Cluster Analysis (n=383) Partitioning groups Total by groups

 2

	2		240			143
	3		240		51	92
	4	69	171		51	92
	5	69	171		51	30	62
	6	69	62	109	51	30	62
	Cluster numbering for the partition into 6 groups	2	5	4	6	3	1

Table 3 . Correspondence matrix between HCA and K-means

 3

	Cluster number from	CHA	2	5	4	6	3	1
	K-means	Total by cluster	69	62	109	51	30	62
	2	62	45	0	4	8	1	4

Table 4 . Inertia decomposition from the HCA and K-means for the partitioning in 6 clusters

 4

	HCA	K-means

Table 5 . Serving frequency of legumes in the IFS sector Serving frequency Contracted-out Self-managed Both

 5

	Less than twice a week	44% (36)	65% (196)	61% (232)
	Twice a week	21% (17)	18% (54)	19% (71)
	More than twice a week	23% (19)	11% (32)	13% (51)
	Everyday	11% (9)	7% (20)	8% (29)
	Number of respondents into brackets. Pearson's Chi-squared test: p.value=0.0024, df=3

Table A4

 A4

	High diversity
	of legumes served
	Low frequency	High frequency
	of legumes	of legumes
	served	served

(in Supplementary Material)

provided all the results from the k-means clustering method. Those profiles are positioned on two discriminant axis: the frequency and the diversity of legumes served. As recalled in Table

1

, the diversity variable is a score based on both the diversity of legumes species and variety of dishes in which legumes are incorporated. * Business segment is more represented in Cluster 2 with a pvalue of 0,15.

P1 -The trend-followers (19%)

				P2 -The innovators (16%)
	Mainly high number of guests Mainly deferred kitchens and more contracted-out More Business, Childcare and Health segments Sustainable food program, alternative dishes Difficulties in cooking legumes Heterogeneous legumes popularity More often France origin and storage org. supply Less organic legume			More medium number of guests Mainly on-site kitchens and self-managed More Business segment Sustainable food program, alternative dishes Facilities in cooking legumes More often high and medium legumes popularity More regional, farmer and storage org. supply More organic legumes Mainly raw legumes uses
	P4 -The elementals (28%)			P3 -The ease-first (9%)
	More low number of guests			More medium number of guests
	Mainly on-site kitchens and self-managed		Various kitchen types and management
	Mainly Education segment			No Business segment
	No sustainable program			Facilities in cooking legumes
	Facilities in cooking legumes Low legumes popularity Mainly France origin and central platform Less often raw legumes uses	Various legumes popularity Mainly central paltform and agrifood industries supply Less raw legumes, more ready-to-cook legumes
	P5 -The reluctants (15%) More low number of guests Various kitchens type and mainly self-managed Mainly Education segment More often no sustainable food program, neither alternative dishes Difficulties in cooking legumes Low legumes popularity Mainly import origin, more often no organic legumes Less often raw legumes uses	Low diversity of legumes	P6 -The traditionals (13%) Mainly very low number of guests Mainly on-site kitchens and more contracted-out Mainly Health segment More often no sustainable food program, neither alternative dishes More often high legumes popularity Mainly central platform supply More often no organic legumes purchase

Table A2 . Shares of contracting-out and self-managing models in France and our sample (n=383)

 A2 Market share from[START_REF] Xerfi | La restauration collective[END_REF]. *Estimated market share from data collected through the open-ended interviews. The number of answers from caterers serving only this segment is reported into parenthesis. There are no official definitions of IFS segments but they are usually divided into 5 subsections that can differ. The Education segment and Business & Administration segment are the most often commonly defined through studies while other segments' delineation can vary

	Data source	Market	Conducted	Answers	Market	Conducted	Answers	Total
		share	survey		share	survey
	IFS MODEL		CONTRACTING-OUT		SELF-MANAGING		BOTH
	SEGMENT
	ALL	40%	21%	81	60%	79%	302	383
	EDUCATION	28%	13%	39	72%	87%	253	292
	BUSINESS AND	72%	42%	24	28%	58%	33	57
	ADMINISTRATION
	HEALTHCARE AND	18%	51%	36	82%	49%	35	71
	ELDERCARE
	CHILDCARE	10%*	26%	23	90%	74%	67	90
	Lecture :

Table A3 . Contracting-out kitchens that declared the name of their company (n=383)

 A3

	Compass	1	203,0	3
	API Restauration	17	104,8	4
	Dupont Restauration	1	40,8	5
	Newrest	9	no data available	6
	Convivio	1	30,1	7
	MRS	0	12,5	8
	Other PCCs	13
	Private Catering Company	Number of	Number of meals per year	Ranking in
	(PCC) name	respondents	(millions) (Xerfi, 2015)	France
	Elior	8	351,3	1
	Sodexo	27	332,4	2

Table A4 . Chi2 test of the variables after the K-means clustering

 A4

	Variables	p.value	df
	Guest number	2,89748E-56	15
	Legume diversity	1,84898E-44	10
	Vacuum-packed legumes	9,12362E-41
	Kitchen type	9,96176E-40
	Education segment	5,26464E-36
	Health segment	2,11214E-26
	Childcare segment	1,66406E-24
	Alternative dishes	1,09137E-22
	Organic legumes	1,13265E-22	15
	IFS model (contracting-out/self-managing)	1,87184E-18
	Legume serving frequency	1,08329E-14	10
	Central Purchase Platform supply chain	6,37597E-13
	Frozen legumes	1,33383E-12
	Difficulties to cook legumes	6,84286E-12
	Sustainable food program	6,88074E-11
	Directly from farmers supply chain	1,07059E-09
	Legumes popularity	1,81045E-09	10
	From storage organisation supply chain	1,14468E-07
	Business segment	1,8377E-07
	Raw legumes	3,17087E-07	10
	Ready-prepared legumes	6,01197E-07
	Dried ingredients	2,93615E-05
	Price factor	0,0004282
	From agrifood industries supply chain	0,00046813
	Geographical origin of legumes	0,003030571	10
	Canned legumes	0,04817604

Table A5 . K-means clustering results: conditional frequencies and statistical tests for Clusters 1 to 3 and 4 to 6

 A5

	Variables Number of guests Legume Diversity Vacuum-packed legumes Kitchen type Education segment Health segment Childcare segment Alternative dishes Organic legumes IFS model Legume serving frequency From central purchase platform Frozen legumes K-Variables Difficulty to cook legumes Sustainable food Difficulty to cook legumes Number of guests program Directly from Sustainable food program Directly from farmer supply chain Legume popularity From storage organisation supply chain Business segment Raw legumes farmer supply chain Legume Diversity Legume popularity Vacuum-packed legumes From storage Kitchen type organisation supply chain Business segment Education segment Raw legumes Health segment Childcare segment Ready-prepared legumes Ready-prepared legumes Alternative dishes Dried ingredient legumes Price factor Dried ingredient legumes Organic legumes From agrifood Price factor industries Geographical From agrifood industries IFS model origin Geographical origin Legume serving Canned legumes Canned legumes purchase platform From central frequency	Modalities Very Low Low Medium High Low Medium High Never or sometimes Regularly Deferred On-site No Yes No Yes No Yes No Yes Never Rarely Often Don't know Contracting-out Self-managing Low Medium Sometimes or regularly Never or sometimes Regularly Modalities High Low No High Very Low Yes Low Low Never No Yes Never Sometimes or regularly Low Medium High Never Sometimes or regularly No Yes Never Sometimes Medium High Sometimes or regularly Low Low Medium Medium High High Never or sometimes Never Regularly Deferred Sometimes or regularly On-site No No Yes Yes Never No Sometimes Yes Regularly No Never Sometimes or regularly Regularly Never Sometimes or regularly Yes No Yes Never or sometimes Regularly Main determinant Never or sometimes Never Not Regularly Rarely Never Main determinant Often Sometimes or regularly Not Don't know National Never Contracting-out Europe or world Sometimes or regularly Self-managing Regional National Low Never or sometimes Europe or world Regional Never or sometimes Sometimes or regularly Never High Medium Regularly	Whole sample 16% 33% 29% 22% 18% 57% 25% 88% 12% 31% 69% 24% 76% 81% 19% 77% 24% 38% 62% 45% 24% 14% 17% 21% 79% 61% 19% 88% 77% 23% Whole 56% 44% sample 44% 56% 16% 56% 44% 33% 72% 44% 56% 72% 28% 40% 47% 13% 80% 20% 85% 15% 14% 22% 29% 22% 28% 18% 40% 57% 47% 25% 13% 88% 80% 12% 31% 20% 69% 85% 24% 15% 76% 14% 81% 22% 19% 64% 77% 80% 20% 64% 80% 20% 24% 38% 62% 63% 37% 56% 63% 45% 44% 37% 24% 59% 56% 14% 41% 44% 17% 35% 59% 21% 21% 41% 79% 44% 35% 61% 63% 21% 44% 63% 88% 12% 21% 19% 37%	Cluster 1 Clu/Mod Mod/Clu p.value 3% 3% 0,000 3% 5% 0,000 13% 19% 0,027 64% 73% 0,000 6% 5% 0,001 20% 58% 0,862 29% 36% 0,010 20% 93% 0,134 11% 7% 0,134 60% 96% 0,000 1% 4% 0,000 21% 26% 0,661 19% 74% 0,661 16% 69% 0,003 32% 31% 0,003 7% 28% 0,000 59% 72% 0,000 9% 18% 0,000 26% 82% 0,000 14% 32% 0,014 30% 36% 0,005 25% 19% 0,225 14% 12% 0,222 28% 31% 0,025 17% 69% 0,025 25% 77% 0,001 15% 15% 0,374 20% 93% 0,117 22% 86% 0,031 11% 14% 0,031 Cluster 4 20% 39% 0,000 38% 61% 0,000 Clu/Mod Mod/Clu p.value 37% 59% 0,000 26% 76% 0,000 17% 9% 0,031 21% 41% 0,000 11% 24% 0,000 47% 55% 0,000 31% 79% 0,032 11% 24% 0,000 26% 76% 0,000 19% 69% 0,576 21% 31% 0,576 20% 41% 0,904 20% 47% 0,914 18% 12% 0,769 16% 66% 0,002 32% 34% 0,002 15% 68% 0,000 42% 32% 0,000 17% 12% 0,664 15% 18% 0,318 23% 24% 0,187 14% 11% 0,001 20% 21% 0,032 9% 6% 0,000 39% 55% 0,000 41% 83% 0,000 25% 42% 0,256 13% 11% 0,000 6% 3% 0,000 31% 98% 0,000 32% 91% 0,001 4% 2% 0,000 8% 8% 0,000 13% 9% 0,001 37% 92% 0,000 32% 96% 0,000 2% 2% 0,000 7% 4% 0,000 36% 98% 0,000 17% 8% 0,052 34% 100% 0,000 35% 27% 0,135 0% 0% 0,000 28% 64% 0,952 33% 91% 0,000 30% 85% 0,155 21% 15% 0,155 21% 70% 0,230 19% 81% 0,890 19% 19% 0,890 11% 9% 0,000 29% 40% 0,605 27% 60% 0,605 33% 75% 0,002 19% 25% 0,002 33% 67% 0,007 19% 61% 0,712 29% 47% 0,704 21% 33% 0,007 20% 39% 0,712 30% 25% 0,616 28% 59% 0,972 21% 61% 0,399 7% 4% 0,000 28% 41% 0,972 17% 39% 0,399 40% 24% 0,021 33% 42% 0,086 19% 59% 0,934 9% 7% 0,000 24% 18% 0,394 19% 41% 0,934 33% 93% 0,000 25% 40% 0,337 26% 47% 0,018 33% 72% 0,004 30% 68% 0,229 18% 19% 0,702 15% 34% 0,046 18% 59% 0,430 30% 95% 0,004 11% 5% 0,004 11% 8% 0,000 30% 20% 0,727 24% 32% 0,229	Cluster 2 v.test Clu/Mod Mod/Clu p.value -3,81 7% 6% 0,022 -6,17 18% 37% 0,444 -2,21 28% 50% 0,000 10,77 5% 6% 0,000 -3,45 0% 0% 0,000 0,17 12% 44% 0,019 2,56 37% 56% 0,000 1,50 17% 95% 0,055 -1,50 7% 5% 0,055 13,45 7% 13% 0,000 -13,45 20% 87% 0,000 0,44 13% 19% 0,382 -0,44 17% 81% 0,382 -2,92 19% 95% 0,001 2,92 4% 5% 0,001 -10,07 19% 90% 0,003 10,07 7% 10% 0,003 -4,19 1% 2% 0,000 4,19 26% 98% 0,000 -2,45 6% 18% 0,000 2,81 19% 27% 0,428 1,21 58% 52% 0,000 -1,22 3% 3% 0,000 2,24 9% 11% 0,033 -2,24 18% 89% 0,033 3,28 10% 37% 0,000 -0,89 24% 27% 0,060 1,57 15% 84% 0,287 2,15 16% 77% 0,994 -2,15 16% 23% 0,994 Cluster 5 -4,05 24% 91% 0,000 4,05 3% 9% 0,000 v.test Clu/Mod Mod/Clu p.value 3,59 21% 64% 0,001 3,87 12% 40% 0,008 -2,16 13% 14% 0,785 -3,59 9% 36% 0,001 -3,87 22% 60% 0,008 5,63 21% 48% 0,010 2,15 18% 89% 0,001 -3,87 7% 19% 0,000 3,87 23% 81% 0,000 -0,56 8% 37% 0,000 0,56 36% 63% 0,000 0,12 5% 13% 0,000 0,11 20% 58% 0,053 -0,29 35% 29% 0,000 -3,03 12% 60% 0,000 3,03 32% 40% 0,000 -4,33 15% 79% 0,156 4,33 23% 21% 0,156 -0,43 4% 3% 0,004 -1,00 7% 10% 0,008 -1,32 16% 32% 0,603 -3,33 4% 5% 0,000 -2,15 6% 11% 0,001 -4,29 64% 80% 0,000 3,73 22% 59% 0,002 6,61 5% 20% 0,000 -1,14 10% 32% 0,018 -3,93 0% 0% 0,000 -4,13 10% 9% 0,305 4,15 16% 96% 0,029 3,48 16% 86% 0,224 -4,15 4% 4% 0,029 -6,32 11% 23% 0,184 -3,48 10% 14% 0,224 6,32 16% 77% 0,184 4,14 16% 93% 0,070 -7,14 4% 7% 0,001 -4,14 7% 7% 0,070 7,14 18% 93% 0,001 -1,95 28% 27% 0,005 6,93 17% 96% 0,001 1,50 15% 23% 0,789 -6,93 3% 4% 0,001 0,06 11% 50% 0,019 4,28 16% 82% 0,287 1,42 15% 84% 0,489 -1,42 12% 16% 0,489 1,20 22% 87% 0,000 0,14 16% 79% 0,752 -0,14 17% 21% 0,752 -4,28 11% 18% 0,287 0,52 33% 86% 0,000 -0,52 3% 14% 0,000 3,08 18% 77% 0,017 -3,08 9% 23% 0,017 2,68 16% 61% 0,487 -0,37 10% 40% 0,000 0,38 23% 70% 0,000 -2,68 13% 39% 0,487 0,37 26% 60% 0,000 0,50 8% 13% 0,031 -0,03 13% 54% 0,375 0,84 10% 34% 0,000 -4,00 7% 7% 0,088 0,03 17% 46% 0,375 -0,84 25% 66% 0,000 2,30 9% 11% 0,176 1,72 15% 36% 0,930 0,08 16% 60% 0,912 -4,67 2% 4% 0,000 -0,85 22% 30% 0,062 -0,08 16% 40% 0,912 4,67 18% 96% 0,000 -0,96 11% 34% 0,098 2,37 11% 24% 0,045 2,86 20% 84% 0,000 1,20 14% 61% 0,645 -0,38 11% 15% 0,195 -1,99 22% 61% 0,003 -0,79 18% 69% 0,296 2,89 10% 57% 0,000 -2,89 52% 43% 0,000 -3,94 4% 5% 0,001 0,35 8% 11% 0,098 -1,20 16% 39% 0,645	Cluster 3 v.test Clu/Mod Mod/Clu p.value -2,29 2% 3% 0,015 0,76 4% 14% 0,008 3,75 17% 53% 0,002 -3,52 13% 31% 0,219 -4,88 3% 6% 0,028 -2,34 10% 61% 0,626 5,92 13% 33% 0,211 1,92 2% 17% 0,000 -1,92 67% 83% 0,000 -3,49 10% 33% 0,723 3,49 9% 67% 0,723 -0,87 9% 22% 0,845 0,87 10% 78% 0,845 3,30 8% 72% 0,152 -3,30 14% 28% 0,152 2,95 10% 81% 0,568 -2,95 8% 19% 0,568 -7,36 8% 33% 0,546 7,36 10% 67% 0,546 -4,88 9% 44% 0,932 0,79 11% 28% 0,522 7,91 2% 3% 0,025 -3,49 14% 25% 0,196 -2,14 12% 28% 0,316 2,14 9% 72% 0,316 -4,05 6% 36% 0,002 1,88 11% 22% 0,544 -1,06 10% 97% 0,059 0,01 3% 25% 0,000 -0,01 31% 75% 6,11 12% 52% 0,574 Cluster 6 -6,11 14% 48% 0,574 v.test Clu/Mod Mod/Clu p.value 3,25 18% 63% 0,007 0,000 -2,66 7% 42% -0,27 58% 73% 0,000 -3,25 8% 38% 0,007 0,076 2,66 12% 58% 0,076 2,56 6% 17% 0,008 3,37 14% 81% 0,109 -4,40 6% 28% 0,038 4,40 12% 72% 0,038 -6,20 9% 72% 0,943 6,20 9% 28% 0,943 -4,99 10% 42% 0,821 1,93 10% 47% 0,949 3,61 8% 11% 0,723 -3,96 9% 78% 0,754 3,96 10% 22% 0,754 -1,42 11% 97% 0,020 1,42 2% 3% 0,020 -2,89 25% 36% 0,000 -2,67 14% 33% 0,098 0,52 4% 8% 0,000 -3,59 1% 2% 0,000 -3,37 8% 19% 0,109 11,40 19% 27% 0,106 3,08 5% 17% 0,000 -6,16 12% 56% 0,886 -2,37 16% 58% 0,089 -5,53 9% 17% 0,175 -1,03 24% 25% 0,019 2,18 13% 94% 0,207 1,22 15% 96% 0,001 -2,18 7% 6% 0,207 -1,33 4% 10% -1,22 3% 4% 0,001 0,001 1,33 16% 90% 1,81 11% 77% 0,112 0,001 -3,40 51% 96% -1,81 19% 23% 0,112 0,000 3,40 1% 4% 2,79 9% 10% 0,486 0,000 3,46 5% 31% 0,27 13% 23% 0,844 0,000 -3,46 46% 69% -2,35 13% 67% 0,718 0,000 1,07 15% 92% 0,69 15% 94% 0,008 0,005 -0,69 4% 6% 0,008 4,31 4% 31% 0,000 -0,32 5% 44% 0,000 0,32 27% 56% 0,000 -1,07 4% 8% 0,005 7,90 20% 60% 0,001 -7,90 8% 40% 2,39 13% 63% 0,973 -2,39 13% 38% 0,973 0,001 0,70 13% 60% 0,555 -3,87 7% 47% 0,050 3,96 19% 69% 0,001 -0,70 11% 40% 0,555 3,87 13% 53% 0,050 -2,16 2% 4% 0,000 -0,89 18% 83% 0,000 -3,87 7% 42% 0,066 -1,71 0% 0% 0,000 0,89 5% 17% 0,000 3,87 13% 58% 0,066 -1,35 20% 27% 0,059 0,09 11% 31% 0,546 0,11 5% 33% 0,001 -3,89 40% 67% 0,000 1,87 11% 19% 0,754 -0,11 15% 67% 0,001 3,89 5% 33% 0,000 -1,66 14% 50% 0,386 -2,00 4% 14% 0,003 4,02 6% 31% 0,000 -0,46 14% 71% 0,260 -1,30 14% 31% 0,139 2,94 12% 56% 0,154 1,05 6% 42% -6,53 14% 98% 0,013 0,006 6,53 2% 2% 0,013 -3,37 31% 52% 0,000 -1,66 11% 17% 0,747 0,46 10% 29% 0,260	v.test -2,44 -2,64 3,08 1,23 -2,20 0,49 1,25 -10,88 10,88 0,35 -0,35 -0,20 0,20 -1,43 1,43 0,57 -0,57 -0,60 0,60 -0,09 0,64 -2,25 1,29 1,00 -1,00 -3,07 0,61 1,89 -7,01 -0,56 0,56 v.test 2,70 7,01 9,84 -2,70 -1,77 -2,63 1,60 1,77 -2,08 2,08 0,07 -0,07 0,23 0,06 -0,35 -0,31 0,31 2,32 -2,32 3,55 -3,66 -1,60 -4,09 -3,64 1,61 1,70 -0,14 2,34 -1,36 3,28 1,26 -1,26 -3,28 -3,47 -1,59 3,47 1,59 11,65 -0,70 -11,65 0,20 -8,33 0,36 8,33 2,66 2,81 -2,66 1,66 -4,27 -5,04 -2,81 3,31 -0,03 0,03 -3,31 0,59 5,04 3,48 -0,59 -1,96 -3,75 3,79 1,96 -3,58 -3,79 -1,84 1,89 -0,60 1,84 7,36 -0,31 -3,22 -7,36 0,87 3,22 -4,35 1,13 -2,93 -2,76 2,48 -2,48 1,43 5,14 1,48 -0,32 -1,13
	Frozen legumes	High Never Regularly Never or sometimes Regularly	21% 12% 37% 77% 23%	8% 11% 21% 31% 17%	8% 7% 41% 86% 14%	0,001 0,117 0,430 0,010 0,010	-3,19 -1,57 0,79 2,58 -2,58	28% 22% 14% 15% 13%	35% 16% 31% 80% 20%	0,004 0,287 0,296 0,568 0,568	2,92 1,06 -1,05 0,57 -0,57	19% 2% 15% 13% 11%	42% 3% 58% 79% 21%	0,003 0,006 0,760 0,059 0,760	2,96 2,76 0,30 -1,89 -0,30

As explained byEdwards (2013:223), "food services" (UK spelling and "foodservices" for American spelling) or "catering" terms describe "the serviced provision of food and beverages (meals) purchased out of the home but which may be consumed both in and out of the home".

Whichever the model, IFS concern a wide variety of guests, both in number and in type: from over 10,000 meals per day for metropolitan schools or major administrations to few meals in rural retirement homes.

By alternative dishes we consider both vegetarian and vegan dishes. As underlined by[START_REF] Dagnelie | 1 -Vegetarian Diets: Definitions and Pitfalls in Interpreting Literature on Health Effects of Vegetarianism[END_REF] there is no clear definition of such dishes in the literature and we adopted the following: vegetarian dishes refer to the exclusion of meat, fish, seafood but not eggs and dairy products; vegan dishes refer to the exclusion of all animalbased products.

 4 In France, see the legislation NOR: AGRG1032380A.

From Kantar World Panel: https://www.kantarworldpanel.com/fr/A-la-une/flexitariens-nl48 [Accessed 10thDecember 2020]

Estimated data from COSELAG project: https://www6.inrae.fr/coselag/Livrables

From French Organic Data: https://www.agencebio.org/wp-content/uploads/2020/07/DP-AGENCE-BIO-CHIFFRES-2019_def.pdf

https://doi.org/10.15454/QR1XMS

https://cran.r-project.org/web/packages/FactoMineR/index.html

Note also that those frequencies are similar to the whole sample based on n=568.

Acknowledgements

Authors acknowledge all the participants in the elaboration of this study and the respondents to the interviews and the survey. Particular acknowledgements are addressed to Muriel Gineste from CISALI, and Marie-Joseph Amiot-Carlin from INRAE, the French Ministry of Agriculture and Food, and everyone who helped us to diffuse it, and Alice Thomson-Thibault for her helpful comments and English editing of the manuscript.

Funding

This work was supported by the European Union's Horizon 2020 research and innovation program under grant agreement No 727672 for the LEGVALUE (Fostering sustainable legume-based farming systems and agrifeed and food chains in the EU) project 2017-2021.

Declaration

On behalf of all authors, the corresponding author states that there is no conflict of interest.

Supplementary Material


Toinon Vigier

Maxime Ameil

Impact of visual immersion on perception of urban morphology and density in 3D city models

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.

Impact of visual immersion on perception of urban morphology and density in 3D city models

Abstract-Urban information visualization is an essential tool for decision process in urban planning. Nowadays, more and more urban visualizations incorporate virtual 3D city scenes to better convey spatial and morphological information. On the other hand, the development of consumer grade VR devices as Head Mounted Displays (HMD) enable to visualize urban information with a greater degree of immersion. These new ways to render and display 3D city models may have a significant impact on the perception of urban morphology and, consequently, on the interpretation of the urban visualization. In this paper, we present a subjective experiment to evaluate the impact of visual immersion -field of view, stereoscopy and allocentric or egocentric representations -on the perception of urban morphology and density in 3D city models. Obtained results can be useful to improve urban visualization, but also to better understand perception, user behavior and navigation in 3D virtual environments.

Index Terms-3D city models, Perception, Urban visualization, Immersion, Head Mounted Display, Virtual reality.

1I NTRODUCTION

Urban information visualization is an essential tool for decision process in urban planning. Nowadays, more and more urban visualizations incorporate virtual 3D city scenes to better convey spatial and morphological information [START_REF] Biljecki | Applications of 3D City Models: State of the Art Review[END_REF]. On the other hand, the development of consumer grade VR devices as Head Mounted Displays (HMD) enable to visualize urban information with a greater degree of immersion. These new ways to render and display 3D city models may have a significant impact on the perception of urban morphology and, consequently, on the interpretation of the urban visualization. In this paper, we propose to evaluate the impact of visual immersion -field of view, stereoscopy and allocentric or egocentric representations -on the perception of urban morphology and density in 3D city models. This study aims at linking the quality of the visualization and the perceived quality of the urban space, in the specific context of density visualization and evaluation.

The paper is organized as follows. Section 2 presents some relative works about urban density, perception of 3D models and impact of visual interfaces on user experience. Then, a subjective experiment about the impact of visual immersion on the perception of urban density and morphology is described in Section 3. The obtained results are presented and discussed in Section 4. Finally, conclusion and future works end the paper in Section 5.

2R ELATED WORKS

Urban density

In urban planning, density analysis is essential because of the constant augmentation of population and services in cities and its impact on the perception and appropriation by final users of their environment [START_REF] -L | Understanding residential density: The relationship between policy, measurement, and perception[END_REF], [START_REF] Bergdoll | Density Perception on Residential Streets[END_REF]. Density is a complex notion based on different aspects as population and dwelling densities, land use intensity, coverage, building height and uniformity, spaciousness, etc [START_REF] Berghauser Pont | Spacematrix: space, density and urban form[END_REF]. Thus, the evaluation of density is not simple and, providing efficient 3D urban visualizations would be helpful for the various actors involved in urban planning. However, because urban density directly depends on urban form, it is important, prior to any visualization of density indicators in 3D city scenes, to qualify how morphology is perceived in 3D urban models.

Perception of 3D models

The perception of urban form of 3D city models can be influenced by the perception of depth, shape and distances in virtual environment, depending on rendering and display features, such as the field of view, the viewpoint, the stereoscopy and the realism.

First of all, several physiological and psychological factors are involved in the perception of depth [START_REF] Mehrabi | Making 3D Work : A Classification of Visual Depth Cues , 3D Display Technologies and Their Applications[END_REF]. Physiological factors are either binocular -e.g. accommodation, vergence, stereopsis (or binocular disparity) -, or monocular -e.g. motion parallax. All the psychological cues are monocular -e.g. retinal image size, linear and aerial perspectives, shadowing and shading. According to the visual interface and the quality of the rendering, the different cues could be more or less effective to perceive depth [START_REF] Mehrabi | Making 3D Work : A Classification of Visual Depth Cues , 3D Display Technologies and Their Applications[END_REF]. On monoscopic screens, mainly psychological cues are used to deduce depth information. On stereoscopic displays, two different images are conveyed to each eye, enabling depth perception thanks to stereopsis. However, stereoscopic devices create ocular and cognitive constraints (e.g. accommodation/vergence conflict) which can damage visual acuity and can lead to visual fatigue [START_REF] Urvoy | How visual fatigue and discomfort impact 3D-TV Quality of Experience : a comprehensive review of technological , psychophysical and psychological factors[END_REF].

On the other hand, 3D city models enable users to modify their viewpoint, moving from egocentric to allocentric representations which can impact perception of space [START_REF] Klatzky | Allocentric and Egocentric Spatial Representations: Definitions, Distinctions, and Interconnections[END_REF]. Moreover, in egocentric representation of virtual environments, distances are judged compressed [START_REF] Witmer | Judging Perceived and Traversed Distance in Virtual Environments[END_REF]. The reasons of this effect are not very clear and different causes can interact, like the field of view of the display and the geometric field of view (field of view of the camera), the lack of realism of the model, etc [START_REF] Willemsen | The effects of head-mounted display mechanical properties and field of view on distance judgments in virtual environments[END_REF], [START_REF] Banton | Effect of Geometric Field of View on Stereoscopic Spatial Judgments[END_REF].

Toinon Vigier 1 Maxime Ameil, Vincent Tourre 2, 3 1 LS2N -Laboratoire des Sciences du Numérique de Nantes 2 AAU -Ambiances, Architectures, Urbanités 3 CRENAU -Centre de recherche nantais Architectures Urbanités For all of these reasons, visual interfaces and visual immersion may influence the way morphology is perceived in 3D urban environments and therefore the way density is derived and evaluated.

Impact of visual interface on user experience

A few studies directly compared user experience and performance while using HMD and desktop. Robertson et al. compared user behavior and navigation between HMD (with head-tracking) and desktop [START_REF] Ruddle | Navigating Large-Scale Virtual Environments: What Differences Occur Between Helmet-Mounted and Desk-Top Displays?[END_REF]. They found that participants were faster with HMD: they adopted a more natural behavior by looking around more while they were moving and they spent less time stationary. Santos et al. compared user performance with HMD and desktop to navigate and catch objects in a game scenario [START_REF] Santos | Head-mounted display versus desktop for 3D navigation in virtual reality : a user study[END_REF]. They found that participants were faster and grabbed more objects while on desktop. However, this results could be biased by user experience: the paper showed that users who rarely played video games usually performed better with HMD. In terms of user experience, participants enjoyed both devices, but more users felt disoriented and sick in the HMD condition comparing to the desktop one. It could be due to technical limitations of the HMD (i.e. low resolution, narrow field of view, low contrasts, discomfort of the cables connecting HMD, etc.).

More recently, some studies focused also on the comparison between TV screen and HMD in terms of enjoyment, attention, presence, etc. [START_REF] Passmore | Effects of viewing condition on user experience of panoramic video[END_REF], [START_REF] Perrin | Towards the Need Satisfaction in Gaming : A comparison of different gaming platforms[END_REF], [START_REF] Macquarrie | Cinematic Virtual Reality : Evaluating the Effect of Display Type on the Viewing Experience for Panoramic Video[END_REF] However, this work concerns entertainment applications and is more distant from our current questions.

3E XPERIMENTAL DESIGN

We present here a subjective study about the perception of urban morphology and density for different visual immersion conditions:

• allocentric or egocentric representations;

• monoscopic desktop screen or stereoscopic HMD device.

This experiment was conducted in the University of Nantes.

Virtual urban environment and stimuli

The stimuli used in this experiment were extracted from a 3D city models of the city of Nantes 1 (France). Ten virtual urban scenes, homogeneous in terms of urban morphology, were manually selected to be assessed by the observers. The scenes are illustrated Figure 1.

The virtual scenes were viewed from two different viewpoints: allocentric or egocentric. In allocentric representation, observers could visualize the 3D city models from a bird's eye view and the urban scene of interest was highlighted in red as we can see Figure 1. In egocentric representation, observers were immersed in the scene in first person view and the urban scene of interest was delimited thanks to semi-transparent walls as we can see Figure 1

Experimental setup

For each scene, the two types of representation, allocentric or egocentric, was visualized on two different devices: desktop or HMD. The desktop screen used in this experiment was a DELL 2208WFPt with a 1680 × 1050 resolution and a 22 inch size. Observers were seated at a desk in front of the computer and used a keyboard and a mouse to interact with the application (see Figure 2a).

The HMD used in this experiment was the HTC Vive with one Vive controller to interact with the application. The viewport resolution of HTC Vive was 1200 × 1080 per eye and the viewing angle was around 110 o in both horizontal and vertical directions. The orientation of the head was tracked with the Vive base stations. The observers were themselves seated comfortably in a turn-chair and were free to rotate the full 360 degrees (see Figure 2b). The application was implemented on Unity 3D.

Navigation and interfaces

On desktop in egocentric representation, participants navigated in the 3D model with arrow keys and the mouse was used to control the camera. In egocentric representation with HMD, participants navigated with the pad of the Vive controller. The camera was controlled thanks to the head tracking.

In allocentric representation, observers could move along an ellipsoid orbit centered on the scene of interest (see Figure 3a). The orbit was initially located at an altitude of 220 meters and observers could zoom in and zoom out from 44 meters to 316 meters above the ground (see Figure 3). Participants could also change the orientation of the camera along the orbit. In desktop condition, observers used the right and left arrow keys to move along the orbit, and the up and down arrow keys to zoom in and out. In HMD, these actions were achieved with the trackpad of the Vive controller. The camera was still controlled with the mouse on desktop and thanks to the head tracking in HMD.

After the visualization of each scene, participants had to answer a questionnaire to evaluate urban morphology. To pause the immersion in the 3D model, users had to right click with the mouse or push the trigger, according to the used device. Then, they had to select, in a 2D menu, whether to continue navigation or to switch to the questionnaire interface. Finally, they had to answer the questionnaire displayed on the screen with the mouse or, in HMD, with the trackpad of the Vive controller.

Experimental protocol

The ten urban scenes were evaluated by each observer in four sessions corresponding to the four viewing conditions: allocentric viewpoint on desktop screen, egocentric viewpoint on desktop screen, allocentric viewpoint in HMD, egocentric viewpoint in HMD.

The order of the sessions were randomized for each observer but, in order to avoid visual fatigue, the two HMD sessions were never done successively. In each session, the ten scenes were also displayed and assessed in a random order.

After each urban scene, the participants had to evaluate their perception of the four following urban characteristics on a 5-point Likert scale: • Density (very low, low, medium, high, very high);

• Building height (very low, low, medium, high, very high);

• Ground space (very narrow, narrow, medium, large, very large);

• Building uniformity (not diverse, slightly diverse, medium, diverse, highly diverse).

After the four sessions, the participants had to fill in a questionnaire where they were asked to rank the four different viewing conditions in terms of:

1) facility to evaluate density; 2) facility to evaluate building height; 3) facility to evaluate ground space; 4) facility to evaluate building uniformity; 5) facility to perceive depth; 6) facility to understand urban morphology; 7) sense of presence in the urban space.

Participants

Twenty-three remunerated observers participated to this experiment. They were aged from 20 to 60 (most of them were students with different backgrounds). Before the experiment, participants were asked to sign a consent form and instructions were given.

4R ESULTS AND DISCUSSION

Impact of visual immersion on urban morphology

Each perceived urban characteristic -density, building height, ground space and building uniformity -can be seen as the dependent variable of a full factorial design where independent factors are:

• Viewpoint (V): allocentric or egocentric;

• Display (D): monoscopic screen or stereoscopic HMD.

Results on 5-point Likert scale were projected from 0 to 4.

Because of the non-normality of the residuals, the statistical analyses were done using Friedman test (i.e. nonparametric version of two-way ANOVA).

Density evaluation

The Friedman test shows that the null hypothesis cannot be rejected for both independent factors, i.e. Viewpoint (χ 2 V (1) = 0.15, p V =0 .70) and Display (χ 2 D (1) = 0.45, p D =0.50).

Surprisingly, and contrary to our expectations, the evaluation of density in 3D city models does not seem to be affected by the viewing mode.

Building height evaluation

The Friedman test shows that the null hypothesis cannot be rejected for the factor Display (χ 2 D (1) = 0.011, p D =0 .92) but can be rejected for the factor Viewpoint (χ 2 D (1) = 45.53, p V < 0.001).

As illustrated by Figure 4, buildings were perceived higher in egocentric than in allocentric representations. Relief tends to be perceived as flattened from a bird's eye point of view. In order to explore the cross effects between factors, a pairwise comparison between all the four viewing modes was performed thanks to the non-parametric Wilcoxon rank sum test (see Table 1). Results show that the factor Viewpoint has a significant effect on building height perception for both desktop and HMD but, as can be seen on Figure 4, the effect seems stronger in HMD. It could be explained by the fact that stereoscopy, as well as a large field of view and the visualization of the buildings at scale 1, may strengthen the impression of height in egocentric representations with HMD.

Ground space evaluation

The Friedman test shows that the null hypothesis can be rejected both for the factor Viewpoint (χ 2 V (1) = 7.68, p V = 0.006) and the factor Display (χ 2 V (1) = 11.13, p D < 0.001). In order to explore the cross effects between factors, a pairwise comparison between all the four viewing modes was performed thanks to the non-parametric Wilcoxon rank sum test (see Table 2). Results show that the viewpoint has a significant effect only in HMD and that the display has a significant effect only for egocentric representation. Indeed, only pairs with HMD Egocentric viewing mode are significantly different, with an overestimation of the ground space (Figure 5). This result disputes previous results which showed that distances are perceived as compressed in egocentric representations of virtual environments [START_REF] Witmer | Judging Perceived and Traversed Distance in Virtual Environments[END_REF]. It may be explained by the fact that a larger field of view in HMD enables, in first person viewpoint, the perception of urban environment in peripheral vision, leading to an impression of higher spaciousness.

Building uniformity evaluation

The Friedman test shows that the null hypothesis cannot be rejected for both independent factors (χ 2 V (1) = 1.57, p V = 0.21 and χ 2 D (1) = 3.44, p D =0 .064). Visual immersion does not seem to impact building uniformity perception. The standard deviation computed on mean opinion scores for each scene was quite low (0.30) comparing to other perceptual characteristics; thus, we can assume that the models had not enough visual cues (e.g. building textures)

Correlation between perceptual urban characteristics

We investigate here if some correlations exist between the evaluation of density, building height, ground space and building uniformity. Table 3 shows the Pearson and Spearman correlation coefficients for each pair of perceptual characteristics. Results show, as expected, a moderate positive correlation between density and building height and a strong negative correlation between density and ground space. They also exhibit a low, but coherent, negative correlation between building height and ground space.

Contrary to what it was shown in situ or in natural pictures [START_REF] Bergdoll | Density Perception on Residential Streets[END_REF], [START_REF] Xu | Density and What Matters: A Study of People's Attitudes Toward and Perceptions of Urban Density[END_REF], no correlation has been found between building uniformity perception and density. It may be due to the absence of details on the 3D city models and, consequently, the difficulty for participants to evaluate uniformity.

Observers preferences

We present here the results of the final questionnaire where participants had to rank the four viewing modes. The answers of two participants, who did not understand well the instructions, were not integrated in the analysis.

Statistical analyses, computed with Friedman test, show that a significant effect of viewing mode on user ranking except for the evaluation of density and ground space (see Table 4). More particularly, egocentric view in HMD was logically preferred to evaluate height and depth as well as to understand urban morphology, whereas allocentric representations on desktop screen obtained the lowest scores (see Figure 6). Participants found difficult to assess building uniformity on egocentric representations displayed on desktop to evaluate uniformity. screen (see Figure 6); probably because of the narrow field of view limits the possibility for observers to compare building shape in a urban scene from a single viewpoint. Finally, participants felt more immersed in HMD and in egocentric viewing modes.

A lot of participants reported a disorientation feeling using allocentric viewpoint with HMD. It may be due to the choice of the interactions (navigation and camera rotation on a fixed orbit) and the absence of reference point.

General discussion

The impact of visual immersion on urban morphology and density perception was evaluated through a subjective experiment where participants had to evaluate urban perceptual characteristics for four different viewing modes, grouped in two factors Viewpoint and Display comprising two levels, respectively Allocentric / Egocentric and Desktop / HMD. We have found that building height was significantly overestimated whatever the display in egocentric representation and that ground space was significantly assessed as larger in HMD egocentric viewing mode. Moreover, subjective results show a moderate positive correlation between density and building height perception and a strong negative correlation between density and ground space perception. Nevertheless, they do not exhibit an impact of visual immersion on density assessment.

Here are some attempts to explain this latter result, rather unexpected. We know that in situ people base their judgment on building height and ground space to evaluate density. It turns out that visual immersion effects on urban morphology perception can offset themselves, while the combination of building height and ground space perception in density evaluation. Indeed, at least for HMD egocentric viewing mode, building are perceived higher but, at the same time, ground space is perceived larger than with the other modes. Considering the sign of the correlations between building height, ground space and density, it could cancel the differences on density evaluation between egocentric viewpoint in HMD and other viewing modes. However, this explanation cannot be valid for desktop display because building are also perceived taller with egocentric viewpoint but ground space is not perceived larger. We could assume that density is a complex and abstract notion based on different urban perceptual characteristics and that correlations between density, building height and ground space are not necessarily direct.

We could also potentially expect that allocentric representations were preferred by participants to assess density by comparison with other areas of the city, but no significant difference have been found between the viewing modes. On the contrary, observers voiced their preference to egocentric view with HMD to assess building height and ground space. These results can be also explained by the fact that density evaluation is based on the combination of an substantial number of urban characteristics, which should be still determined in 3D city models. In addition, these characteristics can differ from virtual environments to reality. Indeed, we have shown that building uniformity was not correlated with density perception in 3D city models without texture whereas it is the case in situ or on natural pictures [START_REF] Xu | Density and What Matters: A Study of People's Attitudes Toward and Perceptions of Urban Density[END_REF].

The main results of this study is useful both for the virtual reality community -to better understand the impact of visual immersion on shape and morphology perception, which can impact user behavior and navigation [START_REF] Ruddle | Navigating Large-Scale Virtual Environments: What Differences Occur Between Helmet-Mounted and Desk-Top Displays?[END_REF], [START_REF] Santos | Head-mounted display versus desktop for 3D navigation in virtual reality : a user study[END_REF] and for the field of urban information visualization. In this sense, the results tend to prove that visual immersion and visual interfaces can influence the way urban morphology is perceived. Consequently, when urban indicators and information are added to the 3D city models, the viewing mode can affect how this new information is interpreted regarding to the form and the physical characteristics of the studied urban area. We can recommend either to adjust the way urban data are visualized in the 3D city models according to the viewing mode, or to propose and advise to users to experiment all of the viewing modes.

In the near future, we plan to confront the subjective answers to objective indicators of urban scene physical morphology, in order to recommend some viewing modes tailored to the provided and displayed urban information. A deeper analysis of user behavior, as attentional processes from head and eye tracking, for the different viewing modes could also be useful to interpret the results obtained here, but also but also to provide valuable insights over the user performance in navigation and other tasks related to shape perception in virtual reality.

5C ONCLUSION

The recent use of 3D city models in urban planning process and the development of consumer grade VR devices raise new questions about the impact of viewing modes and visual immersion on the evaluation of urban characteristics, as morphology and density, from these 3D urban visualizations. To address these questions, we set up an experiment where participants had to evaluate density, building height, ground space and building uniformity of 10 virtual urban scenes of a 3D city model for four viewing conditions: allocentric viewpoint on desktop screen, egocentric viewpoint on desktop screen, allocentric viewpoint in HMD, egocentric viewpoint in HMD. Results mainly show a significant impact of visual immersion on the assessment of building height and ground space. However, despite significant positive -respectively negative -correlation between density evaluation and building height -respectively ground space -perception, we did not discover any significant impact of visual immersion on density. We proposed several hypotheses to explain this unexpected results. In addition, a vast majority of the results obtained here can be useful both for 3D urban visualization and evaluation of user experience and navigation in virtual reality.

  .

  Fig. 2. Experimental setup.

Fig. 1 .

 1 Fig. 1. Screenshots of the 10 urban scenes assessed during the experiment in allocentric (Allo) and egocentric (Ego) representations.

  (a) The orbit on which the user could move in allocentric representation. (b) Initial zoom. (c) Maximal zoom. (d) Minimal zoom.

Fig. 3 .

 3 Fig. 3. Navigation and zoom in allocentric representation.

Fig. 4 .

 4 Fig. 4. Mean Opinion Scores (MOS) for building height evaluation (error bars correspond to standard errors).

Fig. 5 .

 5 Fig. 5. Mean Opinion Scores (MOS) for ground space evaluation (error bars correspond to standard errors).

Figure 5

 5 Figure5shows that observers perceived the ground space larger in egocentric representations and with HMD.In order to explore the cross effects between factors, a pairwise comparison between all the four viewing modes was performed thanks to the non-parametric Wilcoxon rank sum test (see Table2). Results show that the viewpoint has a significant effect only in HMD and that the display has a significant effect only for egocentric representation. Indeed, only pairs with HMD Egocentric viewing mode are significantly different, with an overestimation of the ground space (Figure5). This result disputes previous results which showed that distances are perceived as compressed in egocentric representations of virtual environments[START_REF] Witmer | Judging Perceived and Traversed Distance in Virtual Environments[END_REF]. It may be explained by the fact that a larger field of view in HMD enables, in first person viewpoint, the perception of urban environment in peripheral vision, leading to an impression of higher spaciousness.

  (R) and Spearman (ρ) correlation coefficients between perceptual urban characteristics ( * p<.05; * * p<.001). The correlation coefficients were computed on mean opinion scores (N data = Nscenes × N modes =40).

TABLE 1

 1 Pairwise comparison for building height evaluation.

TABLE 2

 2 Pairwise comparison for ground space evaluation

TABLE 3 Pearson

 3

TABLE 4

 4 Results of Friedman test for all dependent variables with one independent factor (Viewing mode) with 4 levels Fig.6. Mean Opinion Scores (MOS) for viewing condition preferences.