Building a Consistent 3D Representation of a Mobile Robot Environment by Combining Multiple Stereo Views

In this short article, we report new results on our work on the problem of using passive Vision and more precisely Stereo Vision to build up consistent 3D geometric descriptions of the environment of a mobile robot I-INTRODUCTION The robot that we have built consists of a four-wheeled platform with two driving wheels operated by electrical motors. A set of three CCD cameras provides black and white images of the environment The cameras are located at the vertexes of a vertical roughly equilateral triangle. Images are transmitted via a VHF link to a workstation where they are stored and made available through Ethernet to a number of processors. To the user, the vehicle appears as a standard peripheral and can be accessed as such from any terminal on the net It is therefore a very convenient testbed for studying a number of problems in Vision. One such problem is the following. Suppose we let our vehicle wander around in a building using its ultrasound sensors to avoid obstacles, odometry to roughly estimate its motion and its three cameras to compute 3D descriptions of its environment One question then is, can we hope to combine coherently the various sources of information, and especially the visual information obtained at different times and from different places, and build up an accurate geometric 3D representation of the building even if each individual measurement is itself fairly inaccurate 7 We call this problem the Visual Fusion problem. There are two deep issues which are associated with this question. First is the issue of the type of geometric representation that is used by the system. Representations which are mathematically equivalent may behave quite differently on a real problem due to the unavoidable presence of noise and errors. This brings up the second issue which is the question of how do we represent and manipulate uncertainty. In the next Sections we propose a solution to these issues and present some results. ll-WHAT IS THE PROBLEM THAT WE ARE TRYING TO SOL VE ? Each triplet of images provided by the three cameras is analysed by a Stereo program described in [3,4]. This program outputs 3D line segments described in a coordinate system attached to the three cameras. Each line segment has a geometric description which we elaborate on in the next Section and an uncertainty which we explain in Section IV. This uncertainty is directly related to …