Damien Eynard

UAV altitude estimation by mixed stereoscopic vision

Altitude is one of the most important parameters to be known for an Unmanned Aerial Vehicle (UAV) especially during critical maneuvers such as landing or steady flight. In this paper, we present mixed stereoscopic vision system made of a fish-eye camera and a perspective camera for altitude estimation. Contrary to classical stereoscopic systems based on feature matching, we propose a plane sweeping approach in order to estimate the altitude and consequently to detect the ground plane. Since there exists a homography between the two views and the sensor being calibrated and the attitude estimated by the fish-eye camera, the algorithm consists then in searching the altitude which verifies this homography. We show that this approach is robust and accurate, and a CPU implementation allows a real time estimation. Experimental results on real sequences of a small UAV demonstrate the effectiveness of the approach.

Omnidirectional Vision for UAV: Applications to Attitude, Motion and Altitude Estimation for Day and Night Conditions

This paper presents the combined applications of omnidirectional vision featuring on its application to aerial robotics. Omnidirectional vision is first used to compute the attitude, altitude and motion not only in rural environment but also in the urban space. Secondly, a combination of omnidirectional and perspective cameras permits to estimate the altitude. Finally we present a stereo system consisting of an omnidirectional camera with a laser pattern projector enables to calculate the altitude and attitude during the improperly illuminated conditions to dark environments. We demonstrate that omnidirectional camera in conjunction with other sensors is suitable choice for UAV applications not only in different operating environments but also in various illumination conditions.

Multiple camera types simultaneous stereo calibration

Calibration is a classical issue in computer vision needed to retrieve 3D information from image measurements. This work presents a calibration approach for hybrid stereo rig involving multiple central camera types (perspective, fisheye, catadioptric). The paper extends the method of monocular perspective camera calibration using virtual visual servoing. The simultaneous intrinsic and extrinsic calibration of central cameras rig, using different models for each camera, is developed. The presented approach is suitable for the calibration of rigs composed by N cameras modelled by N different models. Calibration results, compared with state of the art approaches, and a 3D plane estimation application, allowed by the calibration, show the effectiveness of the approach. A cross-platform software implementing this method is available1.

HySCaS: Hybrid Stereoscopic Calibration Software

A stereo (or stereoscopic) rig is a device with two or more cameras that makes it possible to simulate human binocular vision and its ability to capture 3D images. The type and number of cameras used depends on the intended application. In the last decade, omnidirectional cameras (standard cameras that point to curved mirrors or use a fisheye lens) have attracted interest because of their wide field of view. However, conventional (perspective) cameras, which have a more limited angle of vision, are still useful. Their images have very high spatial resolution compared to omnidirectional images because, generally, the same number of pixels is used in both cases, although the field of view is smaller in perspective cameras. Therefore, creating a stereo rig with both a perspective and an omnidirectional camera has the potential to merge high spatial resolution with a wide field of view (see Figure 1). Systems that combine different types of cameras on the same rig are called hybrid stereoscopic systems. Their main application fields are video surveillance and localization or navigation in robotics. For instance, a stereo rig with perspective and fisheye cameras can be mounted on a unmanned aerial vehicle (UAV, see Figure 2) to estimate its altitude using images from both cameras (through a method called a plane-sweeping algorithm).1 On the other hand, the attitude of the aircraft, that is, its orientation relative to a reference line or plane, is determined thanks to the fisheye view and using the horizon line or straight lines in urban environments (such as the edge of a building). The field of view of the fisheye lens is wide enough that it can capture the ground—which is projected in the center of the image—and the horizon line—which appears on the border of the picture. Image processing can then detect this reference line and give the attitude of the UAV. Recently, we combined both views to have a precise and robust estimation of UAV motion.2 To retrieve 3D information on the environment and motion of a hybrid stereo rig, the device has to be calibrated first, a process that consists in determining the cameras’ intrinsic and extrinsic parameters. The relative pose—rotation and Figure 1. Example of a hybrid stereo rig: perspective and fisheye cameras.New software simultaneously calibrates conventional and omnidirectional cameras in the same stereoscopic rig.