Digital Photogrammetry and Microscope Photographs

Abstract

The feasibility of applying commercial digital photogrammetric software to the measurement of small objects photographed through an optical microscope has been examined. The objects, about 20 mm across, were photographed using a 35 mm film camera (at the lowest magnification setting of the Olympus microscope) giving photographs at a scale of 2:1. The photographs were then scanned before processing with the VirtuoZo digital photogrammetric system. Various problems needed to be overcome, some due to the limited options available with the highly automated digital system which was not designed for such measurement tasks. The unusual image scales, the uncommon pixel sizes and the unconventional and uncertain imaging geometry, all impeded immediate photogrammetric implementation. Photographic problems with the microscope were also faced, as with all microscope photogrammetry. Creating control points and independently assessing the accuracy of results at these scales were also difficult operations, but an analytical plotter was utilized for both these purposes and to verify the imaging geometry. Once such problems were overcome, image matching proceeded well and an accurate DTM could be created successfully, provided that a suitably textured object was chosen.