Search

With the popularization of RGB-D cameras, access to the third dimension is now possible at low cost. However, these systems have a lower accuracy compared to other technologies such as terrestrial laser scanners (TLS) or mobile laser scanners (MLS). RGB-D cameras have proved their potential for 3D indoor mapping, particularly for Building Information Models reconstruction (Li et al., 2020). This paper aims to investigate the acquisition protocol and propose a method for BIM reconstruction by using an RGB-D camera (Kinect Azure). First, an acquisition protocol is established with the aim of improving the quality of 3D reconstruction of indoor scenes. Different scene cases are considered, namely a single wall, a corridor, a room (with different levels of detail) and two adjacent rooms. After having extracted the best acquisition scenarios for each case of the studied scenes, an image processing is performed for the most complex scenes. Then the 3D reconstruction is performed and the resulting point clouds are subsampled and cleaned. Next, an evaluation of the geometric quality of the 3D reconstruction is performed, by making a comparison between the point clouds from the acquisition protocol (room and corridor) and the reference point clouds from an MLS. The results of this comparison shows that the differences between the two point clouds have an absolute average deviation that doesn’t exceed 4.8mm, which proves that the proposed method has reached competitive accuracy. Finally, segmentation and 3D modeling of the studied scenes are proceeded to extract the BIM objects.

International audience

3D modeling responds to both an economic and an environmental issue, whether at the building or at city scale. Over the past ten years, acquisition techniques have evolved considerably in terms of their speed, the amount of data to be managed, the heterogeneity of information acquired by multi-sensor systems, as well as in terms of processing methods. In this context, new processes such as the “scan-to-BIM” process have emerged. It characterizes the steps leading from point cloud to an intelligent digital model called BIM (Building Information Modeling). By adopting the digital model, building stakeholders are able to perform simulations and reduce, in addition to costs, the environmental impact related to interventions on the building, throughout its life cycle. In practice, to achieve an intelligent digital building model from a survey, many technological obstacles need to be overcome. In this context, I had the chance to supervise various research works on the topics of 3D data acquisition, from the processing of this data to the production of the 3D digital model. Through doctoral research studies that I had the opportunity to co-supervise, I participated in the construction of processing chains on point clouds acquired by airborne LiDAR, terrestrial LiDAR and other 3D sensors. This work has led to the development of innovative acquisition systems (PhD Mittet, 2015), registration algorithms (PhD Hullo, 2013 and PhD Lachat, 2019), segmentation and modeling of point clouds for the reconstruction of buildings (PhD Tarsha-Kurdi, 2008), of facades (PhD Boulaassal, 2010) and of indoor scenes (PhD Macher, 2017). The issue of assessing the quality of models was addressed in every thesis, particularly at the scale of buildings (Mohamed thesis, 2013).Based on the experience acquired through all of this work, we focused also on environmental issues, with the ambition to reconstruct urban trees in 3D. This daring challenge was met, thanks to the collaboration of specialists in urban climatology from the ICube-TRIO team. Finally, a new topic of research has been created within our team: the contribution of laserscanning to urban climate modeling. Urban climate simulation models need truthful 3D models of trees in order to assess the impact of vegetation on the creation of urban microclimates. A first work has shown that the challenge can be faced at the tree level and a park level (PhD Bournez, 2018). The study is currently continuing at city and regional levels (PhD Philipps).In the first part of this work, we will recall the major advances in each step of the established processing chain, before proposing research perspectives. In the "scan-to-BIM" process, the segmentation, up to now mainly geometric, deserves to be enriched with semantic information in order to result in a so-called "digital twin" of the building. The efforts that we will carry out in this direction will also benefit urban climatological models, which require knowledge of urban geometry. To control the errors affecting the models delivered by the processing chain remains a center of interest. In view of our skills and the growing interest of our European countries for a green economy and for energy transition, the future offers good prospects for the development of our team's research topics., La modélisation 3D répond à la fois à un enjeu économique mais aussi environnemental, que ce soit à l'échelle du bâtiment ou de la ville. Ces dix dernières années, les techniques d'acquisitions ont considérablement évolué du point de vue de leur rapidité, du volume de données à gérer, de l’hétérogénéité des informations acquises par les systèmes multi-capteurs, de même que les méthodes de traitement des données. De nouveaux processus sont nés de ces bouleversements, comme le processus « scan-to-BIM » caractérisant les étapes menant du nuage de points à une maquette numérique intelligente. En adoptant la maquette numérique, intégrée dans un processus collaboratif BIM (Building Information Modeling), les acteurs du bâtiment sont en mesure d’effectuer des simulations et de réduire, en plus des coûts, l’impact environnemental lié aux interventions sur le bâtiment, tout au long de son cycle de vie. En pratique, pour aboutir à une maquette numérique intelligente du bâtiment à partir d’un relevé de l’existant, de nombreux verrous technologiques sont à lever. Dans ce contexte, j'ai eu la chance d’encadrer divers travaux de recherches portant sur les thématiques de l’acquisition de données 3D (généralement sous formes de nuages de points 3D) à leur traitement, jusqu’à la production de la maquette numérique.Au travers des thèses que j’ai eu l’occasion de suivre, j’ai participé à la création et la mise en œuvre de chaînes de traitements de nuages de points acquis par LiDAR aéroporté, LiDAR terrestre et autres capteurs 3D. Ces travaux ont permis d’aboutir au développement de systèmes d’acquisitions innovants (thèse Mittet, 2015), d’algorithmes de consolidations (thèses Hullo, 2013 et Lachat, 2019), de segmentation et de modélisations de nuages de points pour la reconstruction de bâtiments (thèse Tarsha-Kurdi, 2008), de façades (thèse Boulaassal, 2010) et d’intérieurs de bâtiments (thèse Macher, 2017). La question de l’évaluation de la qualité des modèles a été abordée dans chacune des thèses, en particulier à l’échelle du bâtiment entier (thèse Mohamed, 2013). Souhaitant mettre au profit de problématiques environnementales l’expérience acquise au travers de l’ensemble de ces travaux de la phase de relevés à celle de la production de la maquette numérique, le regard longtemps focalisé sur le bâtiment s’est alors tourné vers d’autres objets urbains que sont les arbres en ville, avec l’ambition de les reconstruire en 3D. Ce défi audacieux a été relevé, grâce à l’impulsion de spécialistes en climatologie urbaine de l’équipe ICube-TRIO. Il finalement permis de créer un nouvel axe de recherche au sein de notre équipe : l’apport de la lasergrammétrie à la modélisation du climat urbain. En répondant au besoin, pour les modèles de simulation du climat urbain, de disposer de reconstructions 3D fidèles des arbres, nous avons, par la même occasion, été initiés à l’impact des arbres sur la création de microclimats urbains. Débutée à l’échelle de l’arbre et d’un parc (thèse Bournez, 2018), l’étude se poursuit actuellement à l’échelle de la ville et de la région (thèse Philipps, en cours).Nous rappellerons, dans la première partie de ce mémoire, les avancées majeures dans chaque étape de la chaîne de traitements mise en place, avant de proposer des perspectives de recherche. Dans le processus du « scan-to-BIM », la segmentation essentiellement géométrique méritera d’être enrichie d’information sémantique pour aboutir à une maquette numérique de bâtiment intelligente, appelée également « jumeau numérique ». Les efforts que nous mènerons en ce sens seront également profitables aux modèles climatiques urbains, ces derniers exigeant notamment la connaissance de la géométrie urbaine. Le tout sera accompagné d’un souci permanent de maîtriser les erreurs affectant la chaîne de traitement et par voie de conséquence les modèles qui en découlent.Au vu de la sensibilité grandissante de nos pays européens à une économie verte, qui se traduit notamment par l’accompagnement de la transition énergétique, l’avenir laisse entrevoir de belles perspectives d’évolution aux thématiques de recherche de notre équipe.

3D modeling responds to both an economic and an environmental issue, whether at the building or at city scale. Over the past ten years, acquisition techniques have evolved considerably in terms of their speed, the amount of data to be managed, the heterogeneity of information acquired by multi-sensor systems, as well as in terms of processing methods. In this context, new processes such as the “scan-to-BIM” process have emerged. It characterizes the steps leading from point cloud to an intelligent digital model called BIM (Building Information Modeling). By adopting the digital model, building stakeholders are able to perform simulations and reduce, in addition to costs, the environmental impact related to interventions on the building, throughout its life cycle. In practice, to achieve an intelligent digital building model from a survey, many technological obstacles need to be overcome. In this context, I had the chance to supervise various research works on the topics of 3D data acquisition, from the processing of this data to the production of the 3D digital model. Through doctoral research studies that I had the opportunity to co-supervise, I participated in the construction of processing chains on point clouds acquired by airborne LiDAR, terrestrial LiDAR and other 3D sensors. This work has led to the development of innovative acquisition systems (PhD Mittet, 2015), registration algorithms (PhD Hullo, 2013 and PhD Lachat, 2019), segmentation and modeling of point clouds for the reconstruction of buildings (PhD Tarsha-Kurdi, 2008), of facades (PhD Boulaassal, 2010) and of indoor scenes (PhD Macher, 2017). The issue of assessing the quality of models was addressed in every thesis, particularly at the scale of buildings (Mohamed thesis, 2013).Based on the experience acquired through all of this work, we focused also on environmental issues, with the ambition to reconstruct urban trees in 3D. This daring challenge was met, thanks to the collaboration of specialists in urban climatology from the ICube-TRIO team. Finally, a new topic of research has been created within our team: the contribution of laserscanning to urban climate modeling. Urban climate simulation models need truthful 3D models of trees in order to assess the impact of vegetation on the creation of urban microclimates. A first work has shown that the challenge can be faced at the tree level and a park level (PhD Bournez, 2018). The study is currently continuing at city and regional levels (PhD Philipps).In the first part of this work, we will recall the major advances in each step of the established processing chain, before proposing research perspectives. In the "scan-to-BIM" process, the segmentation, up to now mainly geometric, deserves to be enriched with semantic information in order to result in a so-called "digital twin" of the building. The efforts that we will carry out in this direction will also benefit urban climatological models, which require knowledge of urban geometry. To control the errors affecting the models delivered by the processing chain remains a center of interest. In view of our skills and the growing interest of our European countries for a green economy and for energy transition, the future offers good prospects for the development of our team's research topics., La modélisation 3D répond à la fois à un enjeu économique mais aussi environnemental, que ce soit à l'échelle du bâtiment ou de la ville. Ces dix dernières années, les techniques d'acquisitions ont considérablement évolué du point de vue de leur rapidité, du volume de données à gérer, de l’hétérogénéité des informations acquises par les systèmes multi-capteurs, de même que les méthodes de traitement des données. De nouveaux processus sont nés de ces bouleversements, comme le processus « scan-to-BIM » caractérisant les étapes menant du nuage de points à une maquette numérique intelligente. En adoptant la maquette numérique, intégrée dans un processus collaboratif BIM (Building Information Modeling), les acteurs du bâtiment sont en mesure d’effectuer des simulations et de réduire, en plus des coûts, l’impact environnemental lié aux interventions sur le bâtiment, tout au long de son cycle de vie. En pratique, pour aboutir à une maquette numérique intelligente du bâtiment à partir d’un relevé de l’existant, de nombreux verrous technologiques sont à lever. Dans ce contexte, j'ai eu la chance d’encadrer divers travaux de recherches portant sur les thématiques de l’acquisition de données 3D (généralement sous formes de nuages de points 3D) à leur traitement, jusqu’à la production de la maquette numérique.Au travers des thèses que j’ai eu l’occasion de suivre, j’ai participé à la création et la mise en œuvre de chaînes de traitements de nuages de points acquis par LiDAR aéroporté, LiDAR terrestre et autres capteurs 3D. Ces travaux ont permis d’aboutir au développement de systèmes d’acquisitions innovants (thèse Mittet, 2015), d’algorithmes de consolidations (thèses Hullo, 2013 et Lachat, 2019), de segmentation et de modélisations de nuages de points pour la reconstruction de bâtiments (thèse Tarsha-Kurdi, 2008), de façades (thèse Boulaassal, 2010) et d’intérieurs de bâtiments (thèse Macher, 2017). La question de l’évaluation de la qualité des modèles a été abordée dans chacune des thèses, en particulier à l’échelle du bâtiment entier (thèse Mohamed, 2013). Souhaitant mettre au profit de problématiques environnementales l’expérience acquise au travers de l’ensemble de ces travaux de la phase de relevés à celle de la production de la maquette numérique, le regard longtemps focalisé sur le bâtiment s’est alors tourné vers d’autres objets urbains que sont les arbres en ville, avec l’ambition de les reconstruire en 3D. Ce défi audacieux a été relevé, grâce à l’impulsion de spécialistes en climatologie urbaine de l’équipe ICube-TRIO. Il finalement permis de créer un nouvel axe de recherche au sein de notre équipe : l’apport de la lasergrammétrie à la modélisation du climat urbain. En répondant au besoin, pour les modèles de simulation du climat urbain, de disposer de reconstructions 3D fidèles des arbres, nous avons, par la même occasion, été initiés à l’impact des arbres sur la création de microclimats urbains. Débutée à l’échelle de l’arbre et d’un parc (thèse Bournez, 2018), l’étude se poursuit actuellement à l’échelle de la ville et de la région (thèse Philipps, en cours).Nous rappellerons, dans la première partie de ce mémoire, les avancées majeures dans chaque étape de la chaîne de traitements mise en place, avant de proposer des perspectives de recherche. Dans le processus du « scan-to-BIM », la segmentation essentiellement géométrique méritera d’être enrichie d’information sémantique pour aboutir à une maquette numérique de bâtiment intelligente, appelée également « jumeau numérique ». Les efforts que nous mènerons en ce sens seront également profitables aux modèles climatiques urbains, ces derniers exigeant notamment la connaissance de la géométrie urbaine. Le tout sera accompagné d’un souci permanent de maîtriser les erreurs affectant la chaîne de traitement et par voie de conséquence les modèles qui en découlent.Au vu de la sensibilité grandissante de nos pays européens à une économie verte, qui se traduit notamment par l’accompagnement de la transition énergétique, l’avenir laisse entrevoir de belles perspectives d’évolution aux thématiques de recherche de notre équipe.

International audience; The Bronze Age cave “Les Fraux” at Saint-Martin-de-Fressengeas (Dordogne, France) has been discovered in 1989. This site made of a network of galleries of several hundred meters, is a field of investigation for several researchers. This paper will focus on three dimensional contact free measurement techniques for a full 3D-documentation of the structural elements of the cave with some focus on cave art details. In this cave, most of the art is etched in the clay and follows linear, schematic and geometric designs. There are indeed several manmade depictions on the walls and other valuable remains of activity all around the cave. For the archaeologists, the documentation and recording started in 2008 should: - contribute to the accurate indexing of the surveys and images of the remains and collections as well as structural elements and sculptures; - guarantee the indexing compatibility of the data between the different groups of researchers involved in the excavation; - ensure the georeferencing of any type of object in the different parts of the cave. Different techniques based on Terrestrial Laser Scanning (FARO Photon 80), Digital Photogrammetry (CANON EOS 5D images) and Spatial Imaging System (Trimble VX) have been used. The aim of the documentation work is to generate a geometric and photorealistic 3D model from the combination of point clouds and photogrammetric images, for both visualization and accurate documentation purposes. The underground tunnels of the cave are linked to the above terrain with surveying techniques for an accurate georeferencing. The workflow from the raw data to the final PDF-3D model will be discussed. Emphasis will also be given to the deliverables, since the huge amount of data is not directly usable by the archaeologists.

Résumé : La spécification de qualité d’un nuage de points laser est plus pertinente si tous les points ont des qualités individuelles similaires. Pourtant, en pratique, des hétérogénéités de qualité sont causées par la présence de différents matériaux et par la géométrie de la scène qui engendre des hétérogénéités de distances. Cet article s’intéresse à l’hétérogénéité des distances et à son impact sur l’hétérogénéité de la qualité dans un nuage de points. Les acquisitions aussi bien terrestres qu’aériennes sont considérées. Un indicateur simple est proposé pour caractériser l’hétérogénéité des distances et ses effets sur différents critères de qualité. L’analyse de levés lidar terrestre et aérien typiques montre que l’impact de l’hétérogénéité des distances est plus critique dans le cas terrestre. Finalement, des stratégies sont évoquées pour limiter l’hétérogénéité des distances dans un levé lidar, ainsi que des recommandations pour la mise en oeuvre des levés. Abstract : The quality specification of a laser point cloud is more relevant if all points have similar individual qualities. In practice however, quality heterogeneities are caused by the presence of different materials and by the geometry of the scene which produces range heterogeneities. This article focuses on range heterogeneity and its impact on the quality heterogeneity in a point cloud. The analysis of typical terrestrial and aerial lidar surveys shows that the impact of range heterogeneity is more critical in the terrestrial case. Finally, some strategies to limit range heterogeneity in a lidar survey are proposed, as well as recommendations for survey implementation.

International audience; Documentation of our cultural heritage is experiencing an explosion of innovation. New tools have appeared in recent decades including laser scanning, rapid prototyping, high dynamic range spherical and infrared imagery, drone photography, augmented and virtual reality and computer rendering in multiple dimensions. These give us visualisations and data that are at once interesting, intriguing and yet sometimes deceptive.

Surveying fields from geosciences to infrastructure monitoring make use of a wide range of instruments for accurate 3D geometry acquisition. In many cases, the Terrestrial Laser Scanner (TLS) tends to become an optimal alternative to total station measurements thanks to the high point acquisition rate it offers, but also to ever deeper data processing software functionalities. Nevertheless, traditional surveying techniques are valuable in some kinds of projects. Nowadays, a few modern total stations combine their conventional capabilities with those of a laser scanner in a unique device. The recent Trimble SX10 scanning total station is a survey instrument merging high-speed 3D scanning and the capabilities of an image-assisted total station. In this paper this new instrument is introduced and first compared to state-of-the-art image-assisted total stations. The paper also addresses the topic of various laser scanning projects and the delivered point clouds are compared with those of other TLS. Directly and indirectly georeferenced projects have been carried out and are investigated in this paper, and a polygonal traverse is performed through a building. Comparisons with the results delivered by well-established survey instruments show the reliability of the Trimble SX10 for geodetic work as well as for scanning projects.

PosterPoster; From lidar acquisition to FSPM application to 3D urban tree transpiration modeling. 2016 IEEE International Conference on Functional-Structural Plant Growth Modeling, Simulation, Visualization and Applications (FSPMA 2016)

Basic principles of operating Terrestrial Laser Scanners (TLS) are presented in this paper, as well as errors sources, recording modes and data processing methods. Terminology and processing aspects of TLS are defined. A classification of different types of scanners currently available is proposed. In order to assess the accuracy of each point recorded by a laser scanner, we consider all features that may affect the quality of the data produced by a laser scanner. The knowledge of the different errors sources combined to the understanding of the relations between those errors is necessary to quantify data accuracy. Aspects of pre-processing point clouds, direct or indirect georeferencing, registration, segmentation, modelling and texturing are finally presented., Cet article a pour objectif de définir les principes fondamentaux de fonctionnement des Scanners Laser Terrestres (SLT), les sources d 'erreurs, les modes d 'acquisition et les méthodes de traitement des données. Après avoir défini le vocabulaire spécifique et le processus de balayage laser terrestre, une classification détaillée des différents types de scanners disponibles est proposée. Pour estimer la précision de chaque point d 'un levé effectué par un capteur laser, l'ensemble des caractéristiques qui peuvent influencer la qualité des données produites par les appareils utilisés est à considérer. Une bonne connaissance des différentes sources d'erreurs et une compréhension des relations qui les lient est nécessaire pour quantifier la précision des données. Le traitement des données laser terrestre abordent ensuite les étapes de prétraitement, de géoréférencement direct ou indirect, de consolidation ou de recalage, de segmentation, de modélisation et de texturage., Grussenmeyer Pierre, Landes Tania. Lasergrammétrie terrestre. In: Collection EDYTEM. Cahiers de géographie, numéro 12, 2011. Images et modèles 3D en milieux naturels. pp. 11-28.

Communication orale et résumé; absent

International audience; Measurements of glacier surface velocity have been performed on the French Alps Argentière's glacier for more than ten years. Completed by precise other measurements done during the MEGATOR experimentations, the surface velocity could be calculated on one reference point located on the glacial accumulation area. The knowledge of this particular surface velocity allows solving the ambiguity of displacement fields derived from pairs of interferometric synthetic aperture radar (SAR) images acquired by ERS-1/2 satellites. These interferograms provide the surface velocity over large areas. The obtained values are then compared with in-situ precise geodetic measurements of local surface velocities. The similar obtained results permit to validate the described process.

International audience; Airborne laser scanner technique is broadly the most appropriate way to acquire rapidly and with high density 3D data over a city. Once the 3D lidar data are available, the next task is the automatic data processing, with major aim to construct 3D building models. Among the numerous automatic reconstruction methods, the techniques allowing the detection of 3D building roof planes are of crucial importance. For this purpose, this paper studies the Random Sample Consensus (RANSAC) algorithm. Its principle and pseudocode - seldom detailed in the related literature - as well as its complete analyse are presented in this paper. Despite all advantages of this algorithm, it gives sometimes erroneous results. That can be explained by the fact that it uses a pure mathematical principle for detecting the roof planes. So it looks for the best plane without taking into account the particularity of the captured object. The extended RANSAC algorithm proposed in this paper allows harmonizing the mathematical aspect of the algorithm with the geometry of a roof. It is shown that the extended approach provides very satisfying results, even in the case of very weak point density and for different levels of building complexity. Moreover, the adjacency relationships of the neighbouring roof planes are described and analysed. Hence the roof planes are successfully detected and adjacency relationships of the adjacent roof planes are calculate. Finally the automatic building modelling can be carried out easily.

Perched on a granite rock, the Castle of Haut-Andlau is surrounded by forests and ditches which make its access difficult. Only after the first crumbling, the Lord of Andlau worried about its durability and conservation. Since only poor documentation about the castle exists, a complete surveying of the castle was demanded. The problematic became a true challenge, regarding the constraints implied on the one hand by the steep and abrupt terrain surrounding the castle and on the other hand by the dense and broadening vegetation in the immediate vicinity of the castle. In this context, two universities shared their experiences and instruments: the Institute of Photogrammetry and Remote Sensing (Universität Karlsruhe (TH), Germany) and the MAP-PAGE team (INSA de Strasbourg, France). It became rapidly obvious that a unique technique would not overcome the vegetation and relief obstacles. That's why several recording techniques have been investigated. A quality assessment lead to the analysis of the models derived from each technique and to a crucial experience for further campaigns. Therefore, recommendations for an efficient acquisition planning and data processing are gathered. These solutions will help the castle owner to establish the framework of restoration tasks, by showing the destroyed historical structures. Moreover, they will help us to convince the department council to extend these first conclusions to the documentation of numerous other castles of the same type and therefore to insure the future of the Alsatian medieval patrimony.

Airborne laser scanner technique is broadly the most appropriate way to acquire rapidly and with high density 3D data over a city. Once the 3D Lidar data are available, the next task is the automatic data processing, with major aim to construct 3D building models. Among the numerous automatic reconstruction methods, the techniques allowing the detection of 3D building roof planes are of crucial importance. Three main methods arise from the literature: region growing, Hough-transform and Random Sample Consensus (RANSAC) paradigm. Since region growing algorithms are sometimes not very transparent and not homogenously applied, this paper focuses only on the Hough-transform and the RANSAC algorithm. Their principles, their pseudocode - rarely detailed in the related literature - as well as their complete analyses are presented in this paper. An analytic comparison of both algorithms, in terms of processing time and sensitivity to cloud characteristics, shows that despite the limitation encountered in both methods, RANSAC algorithm is still more efficient than the first one. Under other advantages, its processing time is negligible even when the input data size is very large. On the other hand, Hough-transform is very sensitive to the segmentation parameters values. Therefore, RANSAC algorithm has been chosen and extended to exceed its limitations. Its major limitation is that it searches to detect the best mathematical plane among 3D building point cloud even if this plane does not always represent a roof plane. So the proposed extension allows harmonizing the mathematical aspect of the algorithm with the geometry of a roof. At last, it is shown that the extended approach provides very satisfying results, even in the case of very weak point density and for different levels of building complexity. Therefore, once the roof planes are successfully detected, the automatic building modelling can be carried out.

There is an increasing interest of the scientific community in the generation of 3D facade models from terrestrial laser scanner (TLS) data. The segmentation of building facades is one of the essential tasks to be carried out in a 3D modelling process. Since in reality, majority of facade components are planar, the detection and segmentation of geometric elements like planes respond to the previous task. The RANSAC paradigm is a robust estimator and probably the most widely used in the field of computer vision to compute model parameters from a dataset containing outliers. Indeed, RANSAC algorithm is usually successful for fitting geometric primitives to experimental data like for example, 3D point clouds resulting from image matching or from airborne laser scanning. The innovative idea of this study is the application of RANSAC algorithm to TLS data, characterized by a meaningful proportion of outliers. Therefore, this paper presents an approach allowing automatic segmentation and extraction of planar parts of facades scanned by TLS. Firstly, potential planes describing planar surfaces are detected and extracted using RANSAC algorithm. Then, a quality assessment based on manually extracted planes is carried out. The obtained results are evaluated and prove that the proposed method delivers qualitatively as well as quantitatively satisfactory planar facade segments.

This paper highlights the potential to measure temperate glacier velocities and surface characteristics by airborne interferometric and polarimetric SAR remote sensing. Indeed, a novel SAR airborne campaign took place in October 2006 over two Alpine glaciers. Simultaneously to the acquisition of repeat pass interferometric, polarimetric and multi-band data, in-situ measurements were carried out to provide useful information for the SAR synthesis, for backscattering analysis and for performance assessment. Analysis of the experimental data as well as early PolInSAR processing results regarding information extraction are presented.

Mobile mapping techniques represent an efficient way to supply the requirements imposed by the development of 3D GIS, urban digital models and their applications using virtual and augmented reality. The methods widely applied in this domain depend on the video and photogrammetric sensors which provide accurate results but with long time of post-processing. Hence, the integration of a terrestrial laser scanner or terrestrial LiDAR in such mobile mapping platforms would allow obtaining point cloud quickly at low operating cost. However this technique requires an ideal synchronisation between the different components. Each laser pulse has to be strictly synchronized with the GPS/INS module which enables to establish the trajectory of the platform. Terrestrial Laser Scanners (TLS), though, mostly designed for static stations, usually do not give the exact time of each laser pulse. In this paper, we show that under some conditions, it is possible to synchronize point cloud obtained by the TLS with the trajectometry data, in order to achieve the georeferencing of the scanned cloud points into a world coordinate system. We describe the error model and accuracy that one can reach with such a platform, and we illustrate the theoretical results with experimental data obtained by a platform prototype developed at the MAP-PAGE laboratory at INSA of Strasbourg. Thus, we demonstrate that a terrestrial vehicle-borne LiDAR technique can be considered as a novel alternative for the traditional mapping methods.

International audience; Four descending ERS1-2 tandem mode synthetic aperture radar (SAR) interferometric (InSAR) data pairs are used to measure the surface flow field of two alpine glaciers in the French Alps mountains. The topographic component of the interferometric phase is removed by using a digital elevation model (DEM) of the terrain and precise orbit data to reconstruct the ERS InSAR imaging geometry. As one line of sight (LOS) measurement is not suffisant to derive the three dimensional (3D) surface flow field, several different assumptions are considered to determine the missing variables, and to calculate the 3-D surface flow fields. An expert knowledge and the analysis of ten years measurements of the glacier flow allow the detection of areas when the velocity is stationnary during the different seasons. Annual in-situ measurements at the date of the SAR acquisition are taken into account to fix the unknown LOS displacement offset. Finally, a discussion of the four velocity fields observed over different glaciers is proposed and a good agreement with differential GPS measurements is shown.

International audience; Le suivi de l'évolution rapide des glaciers tempérés est important pour des raisons économiques, de sécurité et d'indicateur local des effets du changement global du climat. Comparées aux mesures terrestres dispersées, les acquisitions d'images Radar à Synthèse d'Ouverture (RSO ou SAR) permettent de suivre régulièrement la dynamique des glaciers et apportent des mesures denses des paramètres physiques qui sont nécessaires pour détecter des changements significatifs et contraindre les modèles d'écoulements des glaciers. L'interférométrie RSO ou les techniques alternatives peuvent être appliquées pour mesurer des champs de déplacements qui peuvent être de quelques décimètres par jour dans les Alpes. Les images satellitaires ERS1-2 ont été utilisées pour obtenir des champs de vitesse, principalement en hiver à cause de la forte décorrélation temporelle en été. La polarimétrie RSO peut augmenter le potentiel des observations des surfaces ou des sub-surfaces des glaciers composés de rochers, de neige et de glace. Jusqu'à aujourd'hui, peu de campagnes aéroportées PolSAR ou Pol-InSAR ont été réalisées dans les Alpes. Cette communication présente les premiers résultats d'une campagne d'avion doté d'un capteur SAR qui s'est déroulée en octobre 2006 sur deux glaciers de la vallée de Chamonix : Argentière et Mer de Glace. Grâce à une collaboration entre le DLR (Agence Spatiale Allemande) et le groupe MEGATOR (http://www.lis.inpg.fr/megator), des acquisitions répétées E-SAR ont été effectuées dans les modes interférométriques et polarimétriques dans plusieurs bandes de fréquences ainsi que des mesures in-situ qui vont servir à l'évaluation des performances. Les images E-SAR incluent : 1. Des données polarisées (simples), bande X interférométrique, destinées à la réalisation d'un MNT. 2. Des données polarisées (doubles), bande C qui vont permettre la comparaison entre la haute résolution E-SAR et les données basse résolution ENVISAT. 3. Des données polarisées (" full polar "), bandes L et P interférométriques avec différentes lignes de bases pour l'analyse de la cohérence et à un jour d'intervalle pour l'analyse du déplacement. Les mesures in-situ incluent : 1. Du GPS différentiel pour connaître les positions précises des " corner reflector " et pour obtenir des profils longitudinaux et transversaux des vitesses. 2. Des profils Ground Penetrating Radar (GPR) à différentes fréquences pour étudier les profondeurs de pénétration des ondes électromagnétiques. 3. Des profils stratigraphiques pour mesurer les caractéristiques des strates du manteau neigeux (température, taille des grains...). Les premiers résultats de ces acquisitions uniques en Europe seront présentés ainsi que les axes de recherche qui vont être développés. Des perspectives seront extraites concernant des applications pour l'analyse Pol-InSAR du manteau neigeux et le suivi Pol-InSAR des glaciers tempérés. E-SAR : Experimental Synthetic Aperture Radar PolSAR : Polarimetric Synthetic Aperture Radar Pol-InSAR : Polarimetric-Interferometric Synthetic Aperture Radar Remerciements : Les auteurs souhaitent remercier tous les participants à cette expérimentation : - Ralf Horn, Martin Keller, Christian Andres (DLR-HR Oberpfaffenhofen) - P. Grussenmeyer, M. Koehl, E. Smigel, S. Guillemin (MAP-PAGE, CNRS-INSA Strasbourg), - J.-M. Vanpe, L. Ott (GIPSA-lab, CNRS-INP Grenoble), - I. Petillot, L. Valet, Ph. Bolon (LISTIC, Université de Savoie), - G. Lehureau, L. Denis, F. Tupin (TSI, CNRS-GET Telecom Paris), - N. Longepe, L. Ferro-Famil (IETR, CNRS-Université de Rennes 1), - J. Deparis (LGIT, CNRS-INP Grenoble), - L. Moreau (EDYTEM, CNRS-Université de Savoie), - R. Lecluse (guide). Ainsi que la Société d'Emosson qui nous a autorisés à utiliser ses locaux pour mettre en place des instruments de mesures sous le glacier d'Argentière.

Twenty years of airborne photography, more then ten years of multi-spectral and radar images were a sufficient pretext for creating a cooperation between 4 French laboratories called the MEGATOR Group. Aim of this group is to demonstrate the interest of using high resolution optical and radar data to monitor temperate glacier activity. For this ambitious purpose, it was necessary to reassemble specialists coming from different application fields. Thus, surveyors participate for providing detailed and accurate optical products as well as terrain physical data which will be used in further radar processing steps. The extended abstract presents the results of the measurements and processing products of the MAP-PAGE team, as well as the perspectives of that exciting project.

International audience; The monitoring of temperate glacier activity is one of the applications which require the combined use of optical and SAR data. It should become feasible thanks to the ALOS PRISM and PALSAR sensors. In this paper, we present the interest of using L-band polarimetric interferometric SAR data and high resolution panchromatic stereoscopic data to monitor moving temperate glaciers made of ice, snow and rocks. The scientific issues are described and a test-site located in the Mont-Blanc region in the Alps is proposed for specific experiment and validation. The Mont-Blanc test-site includes two well-known glaciers (Mer-de-Glace and Argentière glaciers) where a large data set has been collected: ERS, RADARSAT and ENVISAT data, airborne E-SAR data (X, C, L and P bands), airborne photographs, GPS and GPR in-situ measurements...

International audience; Temperate glaciers are an indicator of the local effects of global climate change. For economical and security reasons in the surrounding areas, the monitoring of those geophysical objects is being a necessity. SAR data are expected to provide dense measurements of physical parameters which are necessary to detect significant changes and to constrain glacier flow models. In this paper, five descending one-day ERS- 1/2 tandem interferometric data pairs from July 1995 to April 1996 are studied in the Chamonix Mont-Blanc area (French Alps). This multi-temporal interferogram series is used to analyse the coherence levels and fringe patterns over nine glaciers. Moreover, when the coherence is sufficient, Differential SAR Interferometry (D-InSAR) processing are applicable to derive a three-dimensional (3-D) velocity fields. An expert knowledge and a ten years measurements analysis of glacier flow are used to fix the line of sight (LOS) displacement offset. Finally, an analysis of the wrapped phase difference between interferograms is exposed to detect the presence of residual topographic fringes and to characterize the surface flow field evolution.

Airborne laser scanning systems generate 3-dimensional point clouds of high density and irregular spacing. These data consist of multiple returns coming from terrain, buildings, and vegetation. The major difficulty is the extraction of object categories, usually buildings. In the field of disaster management, the detection of building damages plays an important role. Therefore, the question arises, if damaged buildings can also be detected by a method developed for the automatic extraction of buildings. Another purpose of this study is to extend and test an automatic building detection method developed initially for first echo laser scanner data on data captured in first and last echo. In order to answer these two questions, two institutes share their data and knowledge: the Institute of Photogrammetry and Remote Sensing (IPF, Universität Karlsruhe (TH), Germany) and the MAP-PAGE team (INSA de Strasbourg, France). The used 3D LIDAR data was captured over an area containing undamaged and damaged buildings. The results achieved for every single processing step by applying the original and the extended algorithm to the data are presented, analysed and compared. It is pointed out which buildings can be extracted by which algorithm and why some buildings remain undetected