Three-dimensional Photogrammetry in Biology
Close-range convergent, three-dimensional analytical photogrammetry is an established technique that uses disparate perspectives obtained from (digital) images taken from multiple angles, to calculate relative spatial locations of a set of points. 3-D photogrammetry has been extensively used in architecture, archeology, forensic criminology, as well as in geology and space engineering. In Biology, photogrammetry has been largely limited to two-dimensional size estimation and pattern recognition applications. There is no reason however why three-dimensional photogrammetry should not become a viable, practical and accurate tool for the non-invasive assessment of biological systems and their physical environment.
We have tested the validity and accuracy of three-dimensional photogrammetry for contact-free spatial measurements of biological objects. Specifically, we tested how accurate standard morphometric measurements of vertebrates are that are derived from photogrammetric measurements. We also determined the accuracy of non-invasive body mass estimates for pinnipeds based on photogrammetrically derived body volume assessments. In an expansion of this concept, we are testing whether body condition can be estimated from a combination of photogrammetrically derived morphometric measurements.
The image below shows a typical digital still imaging setup used by former Texas A&M M.Sc. student Jason Waite at the Alaska Sea Life Center to obtain images suitable for the reconstruction of 3-D models of Steller sea lions. Four cameras are fairly evenly distributed around the experimental subject - as shown here. A minimum of three different perspectives are needed for 3-D modeling. With more images from different perspectives, accuracy generally increases significantly.
The four images captured in this setup are shown next:
These four images were used to reconstruct this spatially referenced, accurate, three-dimensional wireframe model of the sea lion. This was done using commercially available 3D modeling software: Photomodeler Pro by EOS Systems, Inc.
The application of 3D photogrammetry to volume-based mass estimation of Steller sea lions is described in this publication:
Waite JN, Schrader WJ, Mellish JE, Horning M (2007). Three-dimensional photogrammetry as a tool for estimating morphometrics and body mass of Steller sea lions (Eumetopias jubatus). Canadian Journal ofFisheries & Aquatic Sciences 64: 296-303.
For an application of 3-D photogrammetry, check out our SLiDAP remote imaging project