Highway traffic monitoring on medium resolution satellite images

International audienceThese last years, earth observation imagery has significantly improved. Public satellites such as WorldView-3 can now produce images with a Ground Sample Distance of 31cm, reaching an equivalent resolution than aerial images. Perhaps more importantly, the revisit frequency has also been greatly enhanced: providers such as Planet can now acquire images of an area on a daily basis. These major improvements are fueled by an increasing demand for frequent objects detection. An application generating a particular interest is vehicle detection. Indeed, vehicle detection can give to public and private actors valuable data such as traffic monitoring and parking occupancy rate estimations. Several datasets, such as DOTA or VehSat, already exist, allowing researchers to train machine learning algorithms to detect vehicles. However, these datasets focus on relatively high definition and expensive aerial and satellite images. In this paper, we will present a method for detecting vehicles on medium resolution satellite images, with a GSD comprised between 1 and 5 meters. This approach can notably be used on Planet images, allowing to monitor traffic of an area on a daily basis

Quality performance measures for small capsule endoscopy: Are the ESGE quality standards met?

Background and study aims The European Society of Gastrointestinal Endoscopy (ESGE) recently issued a quality performance measures document for small bowel capsule endoscopy (SBCE). The aim of this nationwide survey was to explore SBCE practice with ESGE quality measures as a benchmark. Patients and methods A dedicated per-center semiquantitative questionnaire based on ESGE performance measures for SBCE was created by a group of SBCE experts. One-hundred-eighty-one centers were invited to participate and were asked to calculate performance measures for SBCE performed in 2018. Data were compared with 10 ESGE quality standards for both key and minor performance measures. Results Ninety-one centers (50.3 %) participated in the data collection. Overall in the last 5 years (2014–2018), 26,615 SBCEs were performed, 5917 of which were done in 2018. Eighty percent or more of the participating centers reached the minimum standard established by the ESGE Small Bowel Working Group (ESBWG) for four performance measures (indications for SBCE, complete small bowel evaluation, diagnostic yield and retention rate). Conversely, compliance with six minimum standards established by ESBWG concerning adequate bowel preparation, patient selection, timing of SBCE in overt bleeding, appropriate reporting, reading protocols and referral to device-assisted enteroscopy was met by only 15.5%, 10.9%, 31.1%, 67.7%, 53.4%, and 32.2% of centers, respectively. Conclusions The present survey shows significant variability across SBCE centers; only four (4/10: 40 %) SBCE procedural minimum standards were met by a relevant proportion of the centers ( ≥ 80 %). Our data should help in identifying target areas for quality improvement programs in SBCE

Observation de la Terre et stéréoscopie

This thesis deals with the problem of computing accurate digital elevationmodels of the Earth's surface from optical images taken by pushbroomobservation satellites. It takes advantage of the collaboration of thedefendant with CNES (the French Space Agency) on the development ofstereo vision tools for Pléiades, the first Earth observation satelliteproducing quasi simultaneous stereo pairs or triplets with small baseline.The first chapter describes a simple pushbroom camera model for observationsatellites orbiting around the Earth and addresses the correction of theacquisition geometry by involving extrinsic information. This chapter proposesa new algorithm to refine the orientation parameters from a set of groundcontrol points, applicable to all pushbroom satellites.With the goal of testing for satellite imaging the thriving exploration ofstereo matching by the computer vision community, the second chapter exploresthe adaptation of the theory of epipolar resampling to pushbroom images.Epipolar resampling is traditionally used in stereo to reduce the matchingcomputational cost, and permits to test for satellite imaging the mostcompetitive computer vision algorithms. The third chapter discusses the effectsof geometric calibration inaccuracies and proposes a method to cancel itsimpact on stereo matching.The fourth chapter analyzes and describes a detailed implementation of theSemi-Global Matching (SGM) algorithm, which is currently among the top-rankedstereo vision algorithms. Based on a recently proposed interpretation of SGM asa min-sum Belief Propagation algorithm, a variant is proposed that allows toreduce by a factor five the energy gap of SGM with respect to referencealgorithms for Markov Random Fields with truncated smoothness terms.By wrapping together the algorithmic blocks described in the previous chapters,the fifth chapter describes S2P, a complete stereo pipeline for producingdigital elevation models from satellite images. As an application, a landscapeevolution model is presented in the sixth chapter. The model is used tosimulate numerically the fine structure of the river networks on digitalelevation models obtained from Pléiades Earth observation images.The source code of the S2P stereo pipeline is distributed as open source. Toensure reproducibility, the algorithms implemented in each step of the S2Ppipeline are submitted to the IPOL journal, with detailed descriptions of thealgorithms, documented source codes and online demonstrations for each block ofthe pipeline.Cette thèse étudie les problèmes posés par l’estimation automatique de modèles numériques d’élévation de la surface terrestre à partir de photographies prises par des satellites. Ce travail a bénéficié d’une collaboration avec le CNES (Centre National d’Etudes Spatiales) sur le développement d’outils de vision stéréoscopique pour Pléiades, le premier satellite d’observation de la Terre capable de produire des paires ou triplets d’images quasi-simultanées. Le premier chapitre de la thèse décrit un modèle simplifié de caméra pushbroom destiné aux satellites d’observation de la Terre, et aborde le problème de la correction des données de calibration en faisant intervenir des mesures externes. Ce chapitre propose un nouvel algorithme pour affiner les paramètres d’orientation du satellite à partir d’un jeu de points de contrôle. Il est utilisable pour tous les satellites munis de caméras pushbroom. Dans le but d’appliquer aux images satellitaires les nombreux algorithmes de mise en correspondance stéréoscopique développés en traitement d’images et en vision par ordinateur, le deuxième chapitre explore l’adaptation de la théorie de la rectification épipolaire aux images prises par des caméras pushbroom. La rectification épipolaire est utilisée habituellement pour réduire la complexité du problème de mise en correspondance stéréoscopique, et permet d’appliquer les algorithmes les plus récents à des images satellitaires. Le chapitre suivant étudie les effets des erreurs de calibration géométrique sur la rectification et propose une méthode pour éliminer leur impact sur la mise en correspondance. Le quatrième chapitre décrit et analyse en détails une implémentation de l’algorithme Semi-Global Matching (SGM), classé actuellement parmi les meilleurs algorithmes de mise en correspondance stéréoscopique. En se fondant sur une réinterprétation récente de SGM, ce chapitre en propose une variante qui permet de réduire d’un facteur cinq son écart en énergie par rapport aux algorithmes de référence pour la minimisation de champs aléatoires de Markov. En assemblant les blocs algorithmiques décrits dans les chapitres précédents, le cinquième chapitre décrit S2P, une chaîne stéréoscopique complète qui produit des modèles numériques d’élévation à partir d’images satellitaires. Un modèle d’évolution de paysage est présenté dans le sixième chapitre comme exemple d’application. Le modèle est utilisé pour simuler numériquement la structure fine du réseau hydrographique sur des modèles numériques d’élévation obtenus à partir d’images prises par Pléiades. Le code source de la chaîne S2P2 est distribué en tant que logiciel open source. Afin d’assurer la reproductibilité des résultats obtenus, les algorithmes implémentés dans S2P sont en cours de publication dans le journal IPOL, accompagnés de descriptions et d’analyses détaillées, de codes sources documentés et de démonstrateurs en ligne

The Bilateral Filter for Point Clouds

International audiencePoint sets obtained by 3D scanners are often corrupted with noise, that can have several causes, such as a tangential acquisition direction, changing environmental lights or a reflective object material. It is thus crucial to design efficient tools to remove noise from the acquired data without removing important information such as sharp edges or shape details. To do so, Fleish-man et al. introduced a bilateral filter for meshes adapted from the bilateral filter for gray level images. This anisotropic filter denoises a point with respect to its neighbors by considering not only the distance from the neighbors to the point but also the distance along a normal direction. This simple fact allows for a much better preservation of sharp edges. In this paper, we analyze a parallel implementation of the bilateral filter adapted for point clouds. Source Code The ANSI C++ source code permitting to reproduce results from the on-line demo is available on the web page of the article 1

The Bilateral Filter for Point Clouds

International audiencePoint sets obtained by 3D scanners are often corrupted with noise, that can have several causes, such as a tangential acquisition direction, changing environmental lights or a reflective object material. It is thus crucial to design efficient tools to remove noise from the acquired data without removing important information such as sharp edges or shape details. To do so, Fleish-man et al. introduced a bilateral filter for meshes adapted from the bilateral filter for gray level images. This anisotropic filter denoises a point with respect to its neighbors by considering not only the distance from the neighbors to the point but also the distance along a normal direction. This simple fact allows for a much better preservation of sharp edges. In this paper, we analyze a parallel implementation of the bilateral filter adapted for point clouds. Source Code The ANSI C++ source code permitting to reproduce results from the on-line demo is available on the web page of the article 1

MGM: A Significantly More Global Matching for Stereovision

International audienceSemi-global matching (SGM) is among the top-ranked stereovision algorithms. SGM is an efficient strategy for approximately minimizing a global energy that comprises a pixel-wise matching cost and pair-wise smoothness terms. In SGM the two-dimensional smoothness constraint is approximated as the average of one-dimensional line optimization problems. The accuracy and speed of SGM are the main reasons for its widespread adoption, even when applied to generic problems beyond stereovision. This approximate minimization, however, also produces characteristic low amplitude streaks in the final disparity image, and is clearly suboptimal with respect to more comprehensive minimization strategies.Based on a recently proposed interpretation of SGM as a min-sum Belief Propagation algorithm, we propose a new algorithm that allows to reduce by a factor five the energy gap of SGM with respect to reference algorithms for MRFs with truncated smoothness terms. The proposed method comes with no compromises with respect to the baseline SGM, no parameters and virtually no computational overhead. At the same time it attains higher quality results by removing the characteristic streaking artifacts of SGM

Attitude Refinement for Orbiting Pushbroom Cameras: a Simple Polynomial Fitting Method

International audienceThis paper describes a simple pushbroom camera model for Earth observation satellites and proposes a new algorithm to refine the orientation parameters of a camera from a set of ground control points. The relative importance of the various orientation parameters is analyzed. On the last generation of high resolution satellites such as Pléiades and WorldView, the attitude angles are shown to be the main contributors to localization errors. Thus the proposed algorithm focuses on refining the attitude angles. It is based on a simple polynomial fitting method. Numerous experiments, which can be reproduced through the online demo associated to this paper, show that the proposed algorithm is able to reduce the localization error by one order of magnitude with only a few ground control points. A geometric simulator for the proposed model is implemented, as well as the attitude refinement algorithm. Source Code The reviewed Python source code implementing a geometric simulator for the camera model and the attitude refinement algorithm is available from the web page of this article 1. Usage instructions and documentation are included in the README.md file of the archive

L1B+: A Perfect Sensor Localization Model for Simple Satellite Stereo Reconstruction from Push-Frame Image Strips

International audienceWe propose a novel method to generate a single image product from a multi-image strip acquired by a push-frame satellite imaging system. The images of the push-frame strips are combined into a large scale mosaic simulating a perfect sensor geometry. The local camera models of the input images are leveraged to produce a new localization model that covers the output mosaic entirely. Among other applications, this simplifies the task of stereo reconstruction enormously: instead of treating multiple stereo pairs of small images, it is possible to reconstruct the entire area covered by the push-frame acquisition using a single pair of mosaics incorporating all the images. We test our method using strips of SkySat L1B scenes and denote the output images as L1B+. To evaluate the quality of the L1B+ images and their localization models, the stereo reconstructions obtained with L1B+ are compared with those obtained with L1B and with a lidar reference model