QUALITE DES MODELES NUMERIQUES DE TERRAIN DERVIES PAR CORRELATION AUTOMATIQUE

Digital Terrain Models are plying an important role as information layer, mainly with the development of geographic information systems, since they describe the topographic surface of the terrain and hence it constitutes a valuable support for the study of variety of geographical and environmental events. With the advent of digital techniques and the advantages they are offering in terms of automation and precision, users are adopting image matching techniques to derive automatically Digital Terrain Models. The quality of these DTM are determined by different factors (photo scale, scanning resolution and software parameterization). This paper is a contribution to evaluate the influence of some of some factors on the final accuracy of DTM derived by correlation. In this respect, different tests were carried out on two photo scales (1/7500 an 1/20000) flown on varying topography. The photos were scanned to 20, 25, 32 and 42 microns pixel sizes and digital terrain models were derived using ViruoZo software from Supresoft. The assessment of the derived DTMs quality was based on qualitative (visual comparisons of contours) and quantitative ( RMS computed from residuals on ground check points) criteria. Results showed that, in rugged terrain, DTM derived from 1/20000 photos are accurate to 32cm, which may enable deriving contours with 1 m interval. The introduction of break lines prior to the correlation seems to have less influence on the accuracy of derived DTM when the generated grid is very dense, but contributes to reduce the editing burden. The high accuracy of automatically derived DTM may contribute to make less tight the map to photo scale ratio. For instance mapping at 1/5000 from 1/20000 photos can preserve the height accuracy, while with conventional methods, height accuracy at 1/5000 map scale is preserved usually for mapping from 1/12000. 1

Modélisation automatique des données LIDAR

Despite progress in computer vision and aerial photogrammetry, automatic reconstruction of three-dimensional scene from images or LIDAR data are one of the complex problems and also a wide field of research. Accurate and detailed 3D models of buildings have a major interest in many fields such as city planning, navigation, planning of networks telecommunication and military simulation, these models should beings powered and updated periodically. Many 3D modeling approaches have been proposed in recent decades that could beings classified according to the data used (satellite image, MNS, point cloud), the type of treatment (parametric or non-parametric) and the rate of human intervention (automatic, semi-automatic or manual). Modeling 3D information in an automated manner is an essential step for the implementation of several current applications that require a high level of LASER data interpretation. Therefore, there is a growing interest in this area of research and an extensive literature. We propose, through this paper, a study of the state of the art of different modeling approaches reported in the literature.  Keywords: Modeling, LIDAR, 3D, AutomaticMalgré les progrès réalisés en vision par ordinateur et en photogrammétrie aérienne, la reconstitution automatique de scène tridimensionnelle à partir des images ou bien des données LIDAR restent l’un des problèmes complexes et aussi un large champ de recherche. Les modèles 3D précis et détaillés des bâtiments ont un intérêt majeur dans plusieurs domaines tels que l’urbanisme, la navigation, la planification des réseaux de télécommunication et la simulation militaire, ces modèles doivent êtres périodiquement alimentés et mis à jour. De nombreuses approches de modélisation 3D ont été proposées durant ces dernières décennies qui pouvaient êtres classées en fonction de la donnée utilisée (Image satellitaire, MNS, Nuage de points), du type du traitement (paramétrique ou non paramétrique) ainsi que le taux d’intervention humaine (automatique, semi automatique ou bien manuel). La modélisation de l’information 3D d’une façon automatique est une étape primordiale pour la mise en œuvre de plusieurs applications actuelles qui nécessitent une interprétation de haut niveau des données LASER. Par conséquent, il existe un intérêt croissant pour ce domaine de recherche et une vaste littérature. Nous proposons, à travers cet article, une étude de l’état de l’art des différentes méthodes de modélisation proposées dans la littératures. Mots clés: Modélisation, LIDAR, 3D, Automatique.   &nbsp