IN-SITU CALIBRATION FOR WIDE-ANGLE, 3-DIMENSIONAL STEREOSCOPIC IMAGE-ANALYSIS

Accurate measurement of three-dimensional object coordinates from ster eoscopic images is an essential element in various applications that r equire three-dimensional position information. Conventionally, optical ray tracing has been the measurement method of choice. However, it re quires accurate knowledge of geometrical and optical parameters, such as the image distance, camera locations relative to the object field, and size, shape, and refractive index of intervening elements, such as apparatus windows. On the other hand, all these parameters need not b e known if an optical transformation method based on an in situ calibr ation experiment is used. Furthermore, the use of in situ calibration not only increases the effective accuracy of the measured three-dimens ional object coordinates but also reduces significantly the computatio nal time compared with conventional optical ray tracing. The computati onal efficiency of the technique used is essential, especially when th e application requires multiple determinations of a large number of th ree-dimensional coordinates, such as is the case with three-dimensiona l particle-tracking velocimetry. The basic concept and formulation of an optical transformation method based on an in situ calibration exper iment is introduced. The technique is first demonstrated with syntheti c data, then case studies with actual in situ calibration data are dis cussed. (C) 1997 Optical Society of America.