Abstract:
The ecological monitoring of threatened species is vital for their survival as it provides
the baselines for conservation, research and management strategies. Wildlife
studies using tracks are controversial mainly due to unreliable recording techniques
limited to two-dimensions (2D). We assess close-range photogrammetry as a lowcost,
rapid, practical and reliable field technique for the digital three-dimensional
(3D) modelling of lion Panthera leo paws and tracks. First, we tested three reconstruction
parameters affecting the 3D model quality. We then compared direct measurements
on the paws and tracks versus the same measurements on their digital
3D models. Finally, we assessed the minimum number of photographs required for
the 3D reconstruction. Masking, auto-calibration and optimization provided higher
reconstruction quality. Paws masked semi-automatically and tracks masked manually
were characterized by a geometric deviation of 0.23 0.18 cm and
0.50 0.33 cm respectively. Unmasked tracks delineated by means of the contour
lines had a geometric deviation of 0.06 0.39 cm. The use of a correction factor
reduced the geometric deviation to 0.03 0.20 cm (pad-masked paws),
0.04 0.35 cm (pad-masked tracks) and 0.01 0.39 cm (unmasked tracks).
Based on the predicted error, the minimum number of photographs required for an
accurate reconstruction is seven (paws) or eight (tracks) photographs. This field
technique, using only a digital camera and a ruler, takes less than one minute to
sample a paw or track. The introduction of the 3D facet provides more realistic
replications of paws and tracks that will enable a better understanding of their
intrinsic properties and variation due to external factors. This advanced recording
technique will permit a refinement of the current methods aiming at identifying
species, age, sex and individual from tracks.
