Estimating animal location from non-overhead camera views

Tracking an animal's location from video has many applications, from
providing information on health and welfare to validating sensor-based
technologies. Typically, accurate location estimation from video is
achieved using cameras with overhead (top-down) views, but structural and
financial limitations may require mounting cameras at other angles. We
describe a user-friendly solution to manually extract an animal's
location from non-overhead video. Our method uses QGIS, an open-source
geographic information system, to: (1) assign facility-based coordinates
to pixel coordinates in non-overhead frames; 2) use the referenced
coordinates to transform the non-overhead frames to an overhead view; and
3) determine facility-based x, y coordinates of animals from the
transformed frames. Using this method, we could determine an object's
facility-based x, y coordinates with an accuracy of 0.13 ± 0.09 m (mean ±
SD; range: 0.01–0.47 m) when compared to the ground truth (coordinates
manually recorded with a laser tape measurer). We demonstrate how this
method can be used to answer research questions about space-use behaviors
in captive animals, using 6 ewe-lamb pairs housed in a group pen. As
predicted, we found that lambs maintained closer proximity to their dam
compared to other ewes in the group and lamb-dam range sizes were strongly
correlated. However, the distance traveled by lambs and their dams did not
correlate, suggesting that activity levels differed within the pair. This
method demonstrates how user-friendly, open-source GIS tools can be used
to accurately estimate animal location and derive space-use behaviors from
non-overhead video frames. This method will expand capacity to obtain
spatial data from animals in facilities where it is not possible to mount
cameras overhead.