Recognition of Center Circles for Encoded Targets in Digital Close-Range Industrial Photogrammetry

Final position of center circles Recognition of encoded targets on the industrial backgrounds are hot topics in digital close-rang industrial photogrammetry. To recognize the encoded targets, the center circles of targets need to be detected above all. A method was proposed to spot the center circles accurately based on some criteria put forward by authors and was realized by the program developed in MatlabR2010a. Firstly, according to the image that was preprocessed by image-binary threshold and Canny edge detection, straight lines in image were deleted and dimension criteria was applied to obtain possible contours of center circles. Then all these contours were fitted to ellipses based on the Least Square Algorithm and the candidate ellipses were remained except those that did not meet the shape criteria. Finally because of shooting error, all candidate ellipses were modified to obtain the positions of encoded targets' center circles precisely. In laboratory, an experiment was conducted to test and verify the theory mentioned above and the result showed the robust of the method in this paper.