3-DIMENSIONAL CAMERA CALIBRATION TECHNIQUE FOR STEREO IMAGING VELOCIMETRY EXPERIMENTS

A three-dimensional camera calibration technique is developed by combi ning two, 2-D camera calibrations for an orthogonal stereo viewing geo metry. The left camera view (YZ view) and the right camera view (XZ vi ew) are calibrated separately and then combined to produce an XYZ (3-D ) calibration routine, Our technique employs three parallel calibratio n planes. One is placed along the main diagonal of the cubic experimen tal chamber, and the other two planes are placed known distances in fr ont of it and behind it within the chamber. Both cameras view the cali bration points on the planes simultaneously. Given the coordinates of a number of points, we use a physical model to determine the exact pix el locations of the calibration points. After inverting the model equa tions, we input the absolute coordinates and measured pixel locations into a least-squares fitting algorithm to obtain the experimental came ra parameters for each camera individually, We then combine the two ca mera views via a ray-tracing method. We calibrated 3-in.(3) (7.62-mm(3 )), 4-in.(3) (10.16-mm(3)), 5-in.(3) (12.70-mm(3)), and 6-in.(3) (15.2 4-mm(3)) chambers with accuracies between 1.66 and 2.01 pixels (0.60 a nd 0.77% of full field), 1.26 and 1.86 pixels (0.43 and 0.63% of full field), 1.16 and 1.34 pixels (0.33 and 0.39% of full field), and 1.91 and 2.49 pixels (0.59 and 0.77% of full field), respectively, using ou r 3-D camera calibration routine. (C) 1997 Society of Photo-Optical In strumentation Engineers.