Performance of a 7-parameter DLT method for the calibration of stereophotogrammetric systems using 1-D transducers.

A method is presented for calibrating stereophotogrammetric systems which are based on 1-D cameras, i.e., able to record only one of the two coordinates relative to the projection of the target point onto the image plane of a camera. This procedure is based on the Direct Linear Transformation, DLT, introduced by Marzan and Karara. The present version (7DLT) is different from the standard 11-parameter DLT (11DLT); it avoids certain non-orthogonality problems arising in usual DLT implementations, whose correction can be obtained by modifying the basic algorithm, at the expense of its simplicity (MDLT). The accuracy assessment of the 7DLT method was carried out both by a computer simulation of a two-camera stereophotogrammetric system, and on real data from three 1-D optoelectronic cameras. The computer simulation permitted us to compare the performance of 7DLT with 11DLT and MDLT. The reconstruction accuracies of the three algorithms were quite similar. When using real 1-D data, a reconstruction accuracy of 0.66 mm RMS error was obtained (mean value for X, Y, Z coordinates) for 18 target points used as calibration control points. The extrapolation accuracy was 1.85 mm RMS for 180 target points lying outside the calibration structure.