Objectif fisheye | EPFL Graph Search

vignette|150px|Fisheye Nikon 2,8/10,5 mm vignette|150px|droite|Fisheye russe plein format Zenitar 2.8/16 mm Un objectif fisheye, raccourci en fisheye (de l'anglais fish eye signifiant « œil de poisson »), ou objectif hypergone, est un objectif photographique ayant pour particularité une distance focale très courte et donc un angle de champ très grand, jusqu'à 180° dans la diagonale, voire dans toute l'image. Il introduit par son principe même une distorsion qui courbe fortement toutes les lignes droites qui ne passent pas par le centre. On ne peut retrouver les angles qu'en projetant l'image sur un écran sphérique. Cette distorsion est un des effets recherchés en photographie créative. Deux utilisations célèbres du fisheye sont les vues subjectives de HAL9000 dans le film 2001, l'Odyssée de l'espace, et la pochette de l'album des Rolling Stones Big Hits (High Tide and Green Grass). Les catégories de fisheye Les objectifs fisheye sont d'une utilisation ponctuelle, aussi b

Habiter la rivière. Construction de logements en zone de revitalisation aquatique

Mathias Valceschini

Ce projet a deux objectifs: améliorer la qualité écologique de la Reuss, célèbre cours d'eau de Suisse centrale et relier le quartier de Emmen en marge de la ville de Lucerne au paysage fluvial qu'offre la rivière. Le projet s'inscrit dans un quartier périphérique très hétérogène et sans structure évidente. Le réaménagement établit un accès à la rive depuis le quartier. Ainsi, la rive n'est plus une zone en retrait de la ville mais une façade pour le quartier. L'intervention permet également de relier le quartier au cheminement de mobilité douce qui longe la rive. Les intersections ainsi générées deviennent les lieux de rencontre entre habitants du quartier et les pendulaires de l'agglomération. Les bâtiments hybrides remplissent deux rôles. Tout d'abord, la tête des bâtiments est disposée perpendiculairement au courant. Cette disposition permet d'offrir des vues paysagères sur le cours d'eau tout en se détournant de l'autoroute située sur la rive opposée. Cela protège la rive d'un érosion trop importante, suite à la décanalisation du tronçon tout en permettant une divagation du cours d'eau. D'autre part, la partie latérale du bâtiment est montée sur pilotis afin de rendre la rive plus perméable. Elle constitue d'autre part une barrière sonore contre les nuisances de l'autoroute. Sa finesse offre une orientation autant vers le Sud, ensoleillé mais bruyant, que vers le reste du quartier, plus calme.

2017

Vision-Based Sense and Avoid Algorithms for Unmanned Aerial Vehicles

Steven Adriaan Roelofsen

The field of Unmanned Aerial Vehicles (UAVs), also known as drones, is rapidly growing, both in terms of size and of number of applications. Civil applications range from mapping, inspection, search and rescue, taking aerial footage, to art show, entertainment and more. Currently, most applications have a human pilot supervising or controlling the vehicles, but UAVs are expected to gain more autonomy with time. To fly in general airspace, used by both general and commercial aviation, a high level of autonomy is required from UAVs. A core functionality required to fly in general airspace is the UAVs' ability to detect and avoid collisions with other aircraft or objects. This functionality is handled by a so called Sense And Avoid (SAA) system. From among several sensors investigated to be used for a SAA system, a vision-based sensor is seen as a good candidate for a SAA system due to its ability to detect and identify a large variety of objects, as well as being close to the human's main mean to detect aircraft and other objects. To be as general as possible, this work focuses on non-cooperative algorithms that do not take assumptions on the motion of other aircraft. This thesis presents algorithms for a vision-based SAA system. It focuses on the relationship between sensing and avoidance, and how the limitations of one constrain the second. In particular, this thesis studies the consequences of the limited Field Of View (FOV) of a camera sensor on the collision avoidance algorithms. Given the assumptions above, the sensing and tracking of other UAVs is performed using cameras with fish-eye lenses that have a large enough FOV for the collision avoidance algorithms to guarantee to be collision-free. The detection of other UAVs is performed using two methods: a marker-based or a marker-less computer vision algorithms. Using the measurements from the computer vision algorithm, the positions and velocities of neighboring UAVs are tracked using a Gaussian mixture probability hypothesis density filter. This tracking algorithm is able to track multiple UAVs while requiring little computational resources, therefore representing a suitable candidate for on-board deployment. In this work, it is mathematically proven that the motion of an UAV has to be constrained according to the FOV of its sensor. Following that result, several collision avoidance algorithms are adapted to ensure collision-free navigation when used with a sensor with a limited FOV. Sensory limitations such as noise, lag, limited range and FOV, and their effects on the performance of collision avoidance algorithms are studied. Experimental work using high-fidelity simulation and real robots shows that algorithms that only use position information from the sensors are overall more reliable, although less efficient (in terms of distance traveled or trajectory smoothness) than algorithms that also use velocity estimates from the sensing system.

EPFL2017

Origin and nature of measurement bias in catadioptric parallel goniophotometers

Marilyne Andersen, Boris Karamata

We briefly categorize and compare parallel goniophotometers, which are instruments capable of simultaneously measuring the far-field distribution of light scattered by a surface or emitted by a source over a large solid angle. Little is known about the accuracy and reliability of an appealing category, the catadioptric parallel goniophotometers (CPGs), which exploit a curved reflector and a lens system. We analyzed the working principle common to all the different design configurations of a CPG and established the specifications implicitly imposed on the lens system. Based on heuristic considerations, we show that the properties of a real (thick) lens system are not fully compatible with these specifications. This causes a bias to the measurements that increases with the acceptance angle of the lens system. Depending on the angular field, the measured sample area can be drastically reduced and shifted relative to the center of the sample. To gain insights into the nature and importance of the measurement bias, it was calculated with our model implemented in MATLAB for the CPG configuration incorporating a lens system with a very large acceptance angle (fisheye lens). Our results demonstrate that, due to the spatio-angular-filtering properties of the fisheye lens, this category of CPGs is so severely biased as to give unusable measurements. In addition, our findings raise the question of the importance of the bias in the other types of CPGs that rely on a lens system with a lower acceptance angle.

2014

Vision-Based Sense and Avoid Algorithms for Unmanned Aerial Vehicles

Steven Adriaan Roelofsen

EPFL2017