Homography-based visual measurement of wheel sinkage for a mobile robot

The wheel sinkage greatly affects the mobility and localization accuracy of a mobile robot in outdoor deformable terrains. A vision-based method to measure the sinkage is presented. It firstly computes the homography between the wheel plane in 3D space and the image plane of a mounted camera. Then identify the wheel rim in the image by the estimated homography. The difference in image intensity is used to detect wheel-terrain contact points. Considering that the imaging procedure is a projection transformation and some geometric properties do not preserve, detected contact points are transformed into the wheel plane with the estimated homography. Finally compute the wheel sinkage in the wheel plane. System errors introduced by existing methods are eliminated. Additionally, the proposed method does not need costly and complex sensors to measure the relative position between the camera and wheel. Results of experiments show its validity and feasibility.