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.

Schematic illustrating the camera setup used to take four time synchronous pictures of a sea lion. A sea lion is sitting in the middle of this setup. The relative positions of four cameras are indicated through four camera models. The four cameras are very evenly distributed around the sea lion, spaced about ninety degrees apart.

The four images captured in this setup are shown next:

one of four images collected from four different perspectives as illustrates in previous schematic, and used to reconstruct a three-dimensional sea lion model

one of four images collected from four different perspectives as illustrates in previous schematic, and used to reconstruct a three-dimensional sea lion model

one of four images collected from four different perspectives as illustrates in previous schematic, and used to reconstruct a three-dimensional sea lion model

one of four images collected from four different perspectives as illustrates in previous schematic, and used to reconstruct a three-dimensional sea lion model

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.

three-dimensional wireframe model of a sitting sea lion’. With suitable software such as Photomodeler, accurate individual spatial measurements can be made on these 3D models, such as length, girth, or volume.

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