Using Digital Images to Reconstruct Three-Dimensional Biological Forms: A New Tool for Morphological Studies

Abstract  We examined two image-based methods, photogrammetry and stereo vision, used for reconstructing the threedimensional form of biological organisms under field conditions. We also developed and tested a third ‘hybrid’ method, which combines the other two techniques. We tested these three methodologies using two different cameras to obtain digital images of museum and field sampled specimens of giant tortoises. Both the precision and repeatability of the methods were assessed statistically on the same specimens by comparing geodesic and Euclidean measurements made on the digital models with linear measurements obtained with caliper and flexible tape. We found no substantial difference between the three methods in measuring the Euclidean distance between landmarks, but spatially denser models (stereo vision and ‘hybrid’) were more accurate for geodesic distances. The use of different digital cameras did not influence the results. Image-based methods require only inexpensive instruments and appropriate software, and allow reconstruction of the three-dimensional forms (including their curved surfaces) of organisms sampled in the field.