Validation of two independent photogrammetric techniques for determining body measurements of gorillas
Jordi Galbany1,*, Tara S. Stoinski2,3, Disier Abavandimwe2, Thomas Breuer4, William Rutkowski5, Nicholas V. Batista6, Felix Ndagijimana2 and Shannon C. McFarlin1,7
|Keywords||photogrammetry, parallel laser, distance meter, gorilla,|
The ability to accurately measure morphological characteristics of wild primates in the field is challenging, yet critical for understanding fundamental aspects of their biology and behavior. Recent studies have shown that digital photogrammetry can be used to non-invasively measure morphological traits of wild primates, as it allows for the determination of geometric properties of objects remotely from photographic images. We report here on a rare opportunity to test this methodology by comparing measurements obtained directly from living great apes to those obtained from photographs. We test the accuracy and precision of two independent photogrammetric techniques, employing the use of parallel lasers and a distance meter, respectively, for obtaining measurements of static objects and captive western lowland gorillas (Gorilla gorilla gorilla) (n = 4) at Zoo Atlanta. For static objects, the mean percent error between corresponding measurements collected by the same observer directly versus using photogrammetry was 0.49–0.74% for the parallel laser method and 0.62–0.76% for the distance meter method. For gorillas, mean percent error between corresponding direct and remote measurements was 2.72–5.20% for the parallel laser method and 2.20–7.51% for the distance meter method. Correlations between direct measurements and corresponding parallel laser and distance meter measurements of gorillas were highly significant with R2 values and slopes approaching 1.0 (parallel lasers: R2 = 0.9989, P < 0.0001; distance-meter: R2 = 0.9990, P < 0.0001). Further, variation between measurements of the same targets collected repeatedly by the same observer, and between different observers, was uniformly low across methods (CV, range = 0.003–0.013). While errors are slightly higher for the distance meter technique, both methods show great promise for addressing a wide range of questions requiring the non-invasive collection of morphological data from wild primates.
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- Department of Anthropology, Center for the Advanced Study of Human Paleobiology, The George Washington University, Washington DC
- Dian Fossey Gorilla Fund International, Atlanta, Georgia
- Zoo Atlanta, Atlanta, Georgia
- Global Conservation Program, Wildlife Conservation Society, Bronx, New York
- Department of Physics, The George Washington University, Washington DC
- Department of Mechanical and Aerospace Engineering, The George Washington University, Washington DC
- Division of Mammals, National Museum of Natural History, Smithsonian Institution, Washington DC
* All Correspondence to: Dr. Jordi Galbany, Department of Anthropology, Center for the Advanced Study of Human Paleobiology, The George Washington University, 800 22nd Street NW, Ste 6000, Washington DC 20052. E-mail: firstname.lastname@example.org
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