3-D Interpretation of Sewer Circular Structures

A practical algorithm for 3-D interpretation of images taken in a sewer by a robot-inspector is presented. Modern sewers made of concrete present regular circular structures originating at the pipe ends as well as at the joints of the pipe sections. These pipe ends and joints provide regular marks on the sewer images and can be used for their 3-D interpretation. The key idea of the paper is to extract from their image projections the 3-D orientations of the circular structures and their distances relative to the robot. We adopt for this purpose a formula for the possible position of a calibrated camera on the basis of the image of a circle of known size. We describe a sequence of image processing operations that perform circle extraction, robust conic fitting and distance calculation based on original images. The reported results are preliminary in the framework of the project aimed at developing an autonomous robot for sewer inspections. We intend to use the approach to facilitate the orientation of the robot while moving in the sewer.