Calibration of an active stereoscopic imaging system

This paper describes the use of a photogrammetric technique for the calibration of a coordinate imaging system based on stereoscopic TV cameras and structured lighting. Experiments with this system showed that the generated 3-D coordinate images were prone to inaccuracies caused by optical distortions in lenses and also by general geometrical distortions due to positioning of the components of the vision system in three-dimensional space. This necessitated the use of a powerful calibration method which took account of all potential sources of error. A particular photogrammetric technique known as direct linear transformation was used for this purpose, resulting in a worst case accuracy of about 4 mm at a range of 1.8 - 2.2 meters. A discussion justifying this choice of calibration technique is presented together with the complete procedure used. The results obtained are analyzed and possible methods for further improvements in the accuracy of the coordinate data are discussed.