Using Line Correspondence Stereo to Measure Surface Orientation

Abstract

Accuracy of geometric measurement of object environments for robotic vision tasks is of increasing importance as these tasks become more sophisticated. This paper is concerned with the accurate measurement of orientations of lines and planar surfaces from two camera stereo. Most existing stereo algorithms build up geometric descriptions from absolute position information about points. We emphasize in this paper the accuracy advantages of determining orientation of lines and planar surfaces using the correspondence of linear features instead of point features. Intuitively, the determination of only orientation from absolute position measurement of points uses too much information which requires the unnecessary accurate calibration of certain camera parameters. Orientation information is invariant to knowledge about absolute positional information. If the orientation of lines are computed from the intersection of planar sheets of projection from a stereo pair of cameras, in the absence of all camera errors, the result is independent of baseline. Orientation of planar surfaces can be determined from the cross product of the orientations of at least two coplanar linear features. It is shown that even in the presence of typical camera errors that measurement of the orientations of lines and surfaces using line correspondence stereo is relatively insensitive to baseline errors. Even more, the measurement of orientation from line correspondence stereo is relatively insensitive to typical localization error on the image plane. As a result orientations of lines and planar surfaces far from the baseline can be measured much better using line correspondence stereo rather than point correspondence stereo. 1