Recalage GPS / SIG / Video, et synthèse de textures de bâtiments

National audienceDans le contexte du recalage de données SIG de bâtiments avec des vidéos -- par exemple pour des applications de réalité augmentée -- nous présentons une solution à un des problèmes les plus critiques, à savoir l'initialisation de ce recalage. La méthode proposée exploite d'une part les informations sémantiques que l'on peut associer aux primitives extraites des images, et d'autre part le principe même de l'algorithme robuste RANSAC pour trouver automatiquement la pose initiale de la caméra d'acquisition. Nous montrons également comment ce recalage peut être exploité pour enrichir la base SIG visualisée par des textures réelles, calculées à partir des images acquises au sol, et ce de façon tout aussi automatique

Using Geometric Constraints for Camera Calibration and Positioning and 3D Scene Modelling

International audienceThis work concerns the incorporation of geometric information in camera calibration and 3D modelling. Using geometric constraints enables stabler results and allows to perform tasks with fewer images. Our approach is interactive; the user defines geometric primitives and constraints between them. It is based on the observation that constraints such as coplanarity, parallelism or orthogonality, are easy to delineate by a user, and are well adapted to model the main structure of e.g. architectural scenes. We propose methods for camera calibration, camera position estimation and 3D scene reconstruction, all based on such geometric constraints. Various approaches exist for calibration and positioning from constraints, often based on vanishing points. We generalize this by considering composite primitives based on triplets of vanishing points. These are frequent in architectural scenes and considering composites of vanishing points makes computations more stable. They are defined by depicting in the images points belonging to parallelepipedic structures (e.g. appropriate points on two connected walls). Constraints on angles or length ratios on these structures can then be easily imposed. A method is proposed that "collects" all these data for all considered images, and computes simultaneously the calibration and pose of all cameras via matrix factorization. 3D scene reconstruction is then performed using many more geometric constraints, i.e. not only those encapsulated by parallelepipedic structures. A method is proposed that reconstructs the whole scene in iterations, solving a linear equation system at each iteration, and which includes an analysis of the parts of the scene that can/cannot be reconstructed at the current stage. The complete approach is validated by various experimental results, for cases where a single or several views are available

Spatially Coherent Geometric Class Labeling of Images and Its Applications

Automatic scene analysis is an active research area and is useful in many applications such as robotics and automation, industrial manufacturing, architectural design and multimedia. 3D structural information is one of the most important cues for scene analysis. In this thesis, we present a geometric labeling method to automatically extract rough 3D information from a single 2D image. Our method partitions an image scene into five geometric regions through labeling every image pixel as one of the five geometric classes (namely, “bottom”, “left ”, “center”, “right”, and “top” ). We formulate the geometric labeling problem as an energy minimization problem and optimize the energy with a graph cut based algorithm. In our energy function, we address the spatial consistency of the geometric labels in the scene while preserving discontinuities along image intensity edges. We also incorporate ordering constraints in our energy function. Ordering constraints specify the possible relative positional labels for neighbor pixels. For example, a pixel labeled as the “left” can not be the right of a pixel labeled as the “right” and a pixel labeled as the “bottom” can not be above a pixel labeled as the “top”. Ordering constraints arise naturally in a real scene. We observed that when ordering constraints are used, the commonly used graph-cut based «-expansion is more likely to get stuck in local minima. To overcome this, we developed new graph-cut moves which we call order-preserving moves. Unlike «-expansion which works for two labels in each move, order-preserving moves act on all labels. Although the global minimum is still not guaranteed, we will show that optimization with order-preserving moves is shown to perform significantly better than «-expansion. Experimental results show that it is possible to significantly increase the percentage of reasonably good labeling by promoting spatial consistency and incorporating ordering constraints. It is also shown that the order-preserving moves performs significantly better than the commonly used «-expansion when ordering constraints are used as there is a significantly improvement in computational efficiency and optimality while the improvement in accuracy of pixel labeling is also modest. in We also demonstrate the usefulness of the extracted 3D structure information of a scene in applications such as novel view generation, virtual scene walk-through, semantic segmentation, scene synthesis, and scene text extraction. We also show how we can apply this order-preserving moves for certain simple shape priors in graph-cut segmentation. Our geometric labeling method has the following main contributions: (i) We develop a new class of graph-cut moves called order-preserving moves, which performs significantly better than «-expansion when ordering constraints are used. (ii) We formulate the problem in a global optimization framework where we address the spatial consistency of labels in a scene by formulating an energy function which encourages spatial consistency between neighboring pixels while preserving discontinuities along image intensity edges. (iii) We incorporate relative ordering information about the labels in our energy function. (iv) We show that our ordering constraints can also be used in other applications such as object part segmentation. (v) We also show how the proposed order-preserving moves can be used for certain simple shape priors in graph-cut segmentation

3D Scene Geometry Estimation from 360∘^\circ Imagery: A Survey

This paper provides a comprehensive survey on pioneer and state-of-the-art 3D scene geometry estimation methodologies based on single, two, or multiple images captured under the omnidirectional optics. We first revisit the basic concepts of the spherical camera model, and review the most common acquisition technologies and representation formats suitable for omnidirectional (also called 360$^\circ$, spherical or panoramic) images and videos. We then survey monocular layout and depth inference approaches, highlighting the recent advances in learning-based solutions suited for spherical data. The classical stereo matching is then revised on the spherical domain, where methodologies for detecting and describing sparse and dense features become crucial. The stereo matching concepts are then extrapolated for multiple view camera setups, categorizing them among light fields, multi-view stereo, and structure from motion (or visual simultaneous localization and mapping). We also compile and discuss commonly adopted datasets and figures of merit indicated for each purpose and list recent results for completeness. We conclude this paper by pointing out current and future trends.Comment: Published in ACM Computing Survey

Analyse de visibilité et géolocalisation en milieu urbain avec un modèle numérique 3D

L'analyse de visibilité est une question importante de la recherche qui peut trouver des applications dans de nombreux domaines: sécurité, conception de réseau sans fil, gestion du paysage, mise en oeuvre d'accès piétonniers .... La prise en compte de la troisième dimension dans le calcul de visibilité est un réel défi. Seules quelques solutions peuvent détecter les obstacles 3D qui limitent l'isovist. Dans cette communication, nous présentons un nouvel algorithme qui peut détecter tous les objets qui bloquent la vue dans un environnement 30 reconstitué numériquement intégrant le relief. Une démonstration avec des données SIG est également effectuée.La reconnaissance automatique des bâtiments est une étape essentielle pour la réalité augmentée et un outil possible pour la géolocalisation d'une prise de vue. Les recherches dans ce domaine n'utilisent pas la localisation par contenu de l'image. Cet article présente une méthodologie pour l'enrichissement d'une base de données urbaine SIG grâce à un descripteur de texture de façade calculé sur des images de référence. Cet indicateur est ensuite utilisé pour retrouver ce bâtiment dans une nouvelle image et le localiser dans une base de données SIG 3D afin d'estimer sa position et son orientation dans le repère de l'appareil photographique qui a pris le cliché. La qualité des résultats obtenus fait l'objet d'une discussion.The isovist or vision field is an interesting topic with many applications in different fields: security, wireless networkdesign, landscape management and analysis, pedestrian access .... Taking in account 3D environment is a verychallenging task. Only a few solutions can detect 3D obstacles that limit the vision field. We present in this paper a newalgorithm that can detect all the objects which block the sight in a 3D environment including the ground surface. A demonstration with GIS data is also given.Building recognition is the first step for augmented reality and the geolocation of the camera. Research in this field usually does not use the content of the image to locate it. This paper presents a methodology for enhancing and complementing a GIS database of buildings with a texture descriptor of the facades by using information extracted from reference images. This descriptor is used to locate any other image by searching similar texture in the image and locate it through the 3D GIS data base. The absolute position and orientation of the camera of the new image can then be computed if camera parameters (i.e. focal length) are known. The quality of the results is presented and discussed.ST ETIENNE-Bib. électronique (422189901) / SudocSudocFranceF

Hybrid sketching : a new middle ground between 2- and 3-D

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Architecture, 2005.Includes bibliographical references (leaves 124-133).This thesis investigates the geometric representation of ideas during the early stages of design. When a designer's ideas are still in gestation, the exploration of form is more important than its precise specification. Digital modelers facilitate such exploration, but only for forms built with discrete collections of high-level geometric primitives; we introduce techniques that operate on designers' medium of choice, 2-D sketches. Designers' explorations also shift between 2-D and 3-D, yet 3-D form must also be specified with these high-level primitives, requiring an entirely different mindset from 2-D sketching. We introduce a new approach to transform existing 2-D sketches directly into a new kind of sketch-like 3-D model. Finally, we present a novel sketching technique that removes the distinction between 2-D and 3-D altogether. This thesis makes five contributions: point-dragging and curve-drawing techniques for editing sketches; two techniques to help designers bring 2-D sketches to 3-D; and a sketching interface that dissolves the boundaries between 2-D and 3-D representation. The first two contributions of this thesis introduce smooth exploration techniques that work on sketched form composed of strokes, in 2-D or 3-D. First, we present a technique, inspired by classical painting practices, whereby the designer can explore a range of curves with a single stroke. As the user draws near an existing curve, our technique automatically and interactively replaces sections of the old curve with the new one. Second, we present a method to enable smooth exploration of sketched form by point-dragging. The user constructs a high-level "proxy" description that can be used, somewhat like a skeleton, to deform a sketch independent of(cont.) the internal stroke description. Next, we leverage the proxy deformation capability to help the designer move directly from existing 2-D sketches to 3-D models. Our reconstruction techniques generate a novel kind of 3-D model which maintains the appearance and stroke structure of the original 2-D sketch. One technique transforms a single sketch with help from annotations by the designer; the other combines two sketches. Since these interfaces are user-guided, they can operate on ambiguous sketches, relying on the designer to choose an interpretation. Finally, we present an interface to build an even sparser, more suggestive, type of 3-D model, either from existing sketches or from scratch. "Camera planes" provide a complex 3-D scaffolding on which to hang sketches, which can still be drawn as rapidly and freely as before. A sparse set of 2-D sketches placed on planes provides a novel visualization of 3-D form, with enough information present to suggest 3-D shape, but enough missing that the designer can 'read into' the form, seeing multiple possibilities. This unspecified information--this empty space--can spur the designer on to new ideas.by John Alex.Ph.D

Interactive construction of 3d models from panoramic mosaics

This paper presents an interactive modeling system that constructs 3D models from a collection of panoramic image mosaics. A panoramic mosaic consists of a set of images taken around the same viewpoint, and a transformation matrix associated with each input image. Our system first recovers the camera pose for each mosaic from known line directions and points, and then constructs the 3D model using all available geometrical constraints. We partition constraints into soft and hard linear constraints so that the modeling process can be formulated as a linearlyconstrained least-squares problem, which can be solved efficiently using QR factorization. The results of extracting wire frame and texture-mapped 3D models from single and multiple panoramas are presented.

Interactive Construction of 3D Models from Panoramic Mosaics

This paper presents an interactive modeling system that constructs 3D models from a collection of panoramic image mosaics. A panoramic mosaic consists of a set of images taken around the same viewpoint, and a transformation matrix associated with each input image. Our system first recovers the camera pose for each mosaic from known line directions and points, and then constructs the 3D model using all available geometrical constraints. We partition constraints into soft and hard linear constraints so that the modeling process can be formulated as a linearlyconstrained least-squares problem, which can be solved efficiently using QR factorization. The results of extracting wire frame and texture-mapped 3D models from single and multiple panoramas are presented. 1 Introduction A great deal of effort has been expended on 3D scene reconstruction from image sequences (with calibrated or uncalibrated cameras, e.g., [FSL + 95]) using computer vision techniques. Unfortunately, the results f..