Online distance recovery for a sewer inspection robot

An algorithm for online distance computation based on images taken in a sewer by a robot-inspector is presented. Modern concrete sewers are made of standard cylindrical pipes separated by manhole junction areas. Circular structures typically originate at the pipe ends and entrances as well as at the joints of the pipe sections. These structures provide regular marks on the sewer images and can be used for their 3D interpretation. After each robot motion, we extract these circular structures from camera images, and recover their distance relative to the robot. The use of a laser-based orientation method to ensure almost parallel viewing direction of the robot head with respect to the pipe axis drastically simplifies the necessary image processing operations. The method is applied to real image sequences taken in a sewer test-net. Our results show that pipe ends and junctions can be reliably detected by the robot. We intend to use the approach to facilitate robot navigation for sewer inspection