[D] 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 are currently testing the validity and accuracy of three-dimensional photogrammetry for contact-free spatial measurements of biological objects. Specifically, we are testing how accurate standard morphometric measurements of vertebrates are that are derived from photogrammetric measurements. In an expansion of this concept, we are determining the accuracy of non-invasive body mass estimates for pinnipeds based on photogrammetrically derived body volume assessments.
In the image below, you can observe a typical digital still imaging setup used by 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.
Viewing 3-D models
You can download and view three-dimensional models, providing your browser is VRML enabled (VRML = Virtual Reality Modeling Language). To test whether your browser is VRML enabled, go to the Web-3D VRML Browser detector website by the NIST. This site will tell you whether your browser is VRML enabled, and will suggest compatible VRML plugins and link you to free downloads. Alternatively, you can directly download the free Cosmo Player VRML plug-in. For Windows 2000, we have had best luck with the free Blaxxun Contact 4.4 plug-in. With a 3-D enabled browser, you can rotate the 3-D wire-frame models, zoom in and out, and look at the models from any angle.
A sample 3-D model of a Steller sea lion
From the four images shown in above camera perspectives, Jason assembled the sample 3-D model of Woody, a six-year old male Steller sea lion held at the Alaska SeaLife Center, shown below (you need a VRML enabled browser to view this 3-D model). This model was assembled using Photomodeler Pro 3.0 software (EOS Inc.).
[D] Click on the thumbnail
of Woody to view a 3-D model of a Steller sea lion.
On such a three-dimensional model, spatial measurements can be made with a "virtual tape measure", using the Photomodeler software. In the image below, the location of such measurements is highlighted by bright tape placed on an anesthesized sea lion at the Alaska Sea Life Center. Jason analysed the accuracy of the virtual tape measure, and has found the photogrammetric measurement estimates to be accurate within ±1.7 - 2.1% of actual ones.
[D] Click on image to enlarge.
You can read up on details of Jason Waite's preliminary results by downloading the FASEB Experimental Biology 2000 conference poster Jason presented in San Diego in April 2000 (257 Kb pdf file).
Check out the page on Jason's Body Composition Telemetry work in the <PROJECTS> section.
LABB Site map for disability access
This page is HTML 4.0 Transitional validated with the exception of mouseover-effects, wich do not conform to HTML standard, in order to maintain Netscape compatibility (Netscape mouseover effects are non-functional with HTML 4.0 Transitional).