STATISTICAL COMPARISON OF DLT VERSUS ILSSC IN THE CALIBRATION OF A PHOTOGRAMMETRIC STEREO-SYSTEM

This paper compares the DLT and ILSSC approaches in the geometrical ca libration of a photogrammetric stereo-system in terms of accuracy and speed. To come up with an unbiased quantitative evaluation of the accu racy of the algorithms, the concept of reliable estimate has been intr oduced: the statistical distribution of the accuracy is assessed over different calibration experiments performed with the same data but wit h different noise distribution and different test sets. Results show t hat in the simulations where the only error on the two-dimensional poi nts was Gaussian, zero mean, and on real data which were corrected for distortions through polynomial or linear interpolation, the accuracy of the two methods was quite similar. DLT showed more accurate than IL SSC on simulated data with residual distortion errors and on real data which were not corrected for distortions. As far as speed is concerne d, a fast triangulation algorithm is associated with ILSSC while the s imultaneous solution of two pairs of DLT equations is associated to DL T. The first algorithm is much faster, requiring 113 flops per point v ersus 259 of DLT; the fast triangulation with DLT parameters does not achieve the same accuracy on the reconstructed three-dimensional posit ion. Taken all together the results suggest that ILSSC can be theoreti cally considered the best approach to three-dimensional reconstruction , provided that distortions are corrected in advance. The statistical evaluation of the accuracy allows a fair judgement of the performances of the algorithms to be obtained, unbiased by particular distribution s of measurement errors and test points. (C) 1997 Elsevier Science Ltd .