Pose estimation of tube-shaped flexible objects from geometrically rectified shadow images

In this paper, we propose a method to estimate the pose of tube-shaped flexible objects from their shadow cast on non-planar backgrounds. To compensate for the distortion of the shadow by the non-planar backgrounds, we introduce a model-based method to calculate a look-up-table that enables scene-specific undistortion of shadow images if the geometric relations of camera, background and light source are known. In accordance with the established term image rectification that is used to correct images for camera lens errors we propose the term geometric rectification for this process. It is shown how to estimate the 3d position of tube-shaped flexible objects from geometrically rectified shadow images. For unknown lamp positions, we present a method to estimate the position of the point light from an image showing a special calibration rig. The method is verified on synthetic and real world example images taken from Industrial Machine Vision applications.