21 Omnidirectional Vision-Based Control From Homography Youcef Mezouar, Hicham Hadj Abdelkader and Philippe Martinet LASMEA / Blaise Pascal University France 1. Introduction Vision-based servoing schemes are flexible and effective methods to control robot motions from cameras observations (Hutchinson et al 1996). They are traditionally classified into three groups, namely position-based, image-based and hybrid-based control (Espiau et al 1992), (Hutchinson et al 1996), (Malis et al 1999). These three schemes make assumptions on the link between the initial, current and desired images since they require correspondences between the visual features extracted from the initial image with those obtained from the desired one. These features are then tracked during the camera (and/or the object) motion. If these steps fail the visually based robotic task can not be achieved. Typical cases of failure arise when matching joint images features is impossible (for example when no joint features belongs to initial and desired images) or when some parts of the visual features get out of the field of view during the servoing. Some methods have been investigated to resolve this deficiency based on path planning (Mezouar et al 2002), switching control (Chesi et al 2003), zoom adjustment (Benhimane et al 2003). However, such strategies are sometimes delicate to adapt to generic setup. Conventional cameras suffer thus from restricted field of view. There is significant motivation for increasing the field of view of the cameras. Many applications in vision- based robotics, such as mobile robot localization (Blaer et al 2002) and navigation (Winter et al 2000), can benefit from panoramic field of view provided by omnidirectional cameras. In the literature, there have been several methods proposed for increasing the field of view of cameras systems (Benosman et al 2000). One effective way is to combine mirrors with conventional imaging system. The obtained sensors are referred as catadioptric imaging systems. The resulting imaging systems have been termed central catadioptric when a single projection center describes the world-image mapping. From a theoretical and practical view point, a single center of projection is a desirable property for an imaging system (Baker et al 1999). Baker and Nayar in (Baker et al 1999) derive the entire class of catadioptric systems with a single viewpoint. Clearly, visual servoing applications can also benefit from such sensors since they naturally overcome the visibility constraint. Vision-based control of robotic arms, single mobile robot or formation of mobile robots appear thus in the literature with omnidirectional cameras (refer for example to (Barreto et al 2002), (Vidal et al 2003), (Mezouar et al 2004). Image-based visual servoing with central catadioptric cameras using Source: Vision Systems: Applications, ISBN 978-3-902613-01-1 Edited by: Goro Obinata and Ashish Dutta, pp. 608, I-Tech, Vienna, Austria, June 2007 Open Access Database www.i-techonline.com