NLT and extrapolated DLT: 3-D cinematography alternatives for enlarging the volume of calibration

This study investigated the accuracy of the direct linear transformation (DLT) and non-linear transformation (NLT) methods of 3-D cinematography/videography. A comparison of standard DLT, extrapolated DLT, and NLT calibrations showed the standard (non-extrapolated) DLT to be the most accurate, especially when a large number of control points (40–60) were used. The NLT was more accurate than the extrapolated DLT when the level of extrapolation exceeded 100%. The results indicated that when possible one should use the DLT with a control object sufficiently large as to encompass the entire activity being studied. However, in situations where the activity volume exceeds the size of oneʹs DLT control object, the NLT method should be considered.