Digital very close range photogrammetry of a test object incorporating optical texture

Abstract

A digital camera and fixed lens has been used to obtain convergent stereo-pairs of a test object prepared from an experimental material containing optical texture. This is part of a project developing a stereophotogrammetric technique for mapping individual human teeth. VirtuoZo (v3.3) photogrammetric workstation was used to process images with convergent geometries of 2 to 25 degrees and to generate DEMs. The precision of DEMs was typically around 10 μm for convergences of 4 to 25 degrees, decreasing to over 20 μm for convergence below 4 degrees. Relatively constant precision at the different convergence angles was attributed to improved image point measurement precision with decreasing convergence, with measurement precision estimated to be 0.6 μm (0.08 pixels) at 4 degrees and 2.8 μm (0.38 pixels) at 25 degrees. Photogrammetric solutions were not highly stable, with successive solutions at all convergence angles showing small variations in exterior orientation parameters. These variations in exterior orientation parameters were associated with systematic model height errors of up to 80 μm. It was concluded that the single camera and imaging geometry used was not reliably forming models of a tooth sized object given a need to achieve sub-30μm accuracy, intended for the monitoring of tooth surface loss.