Three-dimensional measurements of animal paths using handheld unconstrained GoPro cameras and VSLAM software

Abstract

I present the system PATMOS (paths and tessellated meshes from ORB_SLAM2) for measuring three-dimensional paths of animals in situ using two handheld GoPro cameras and a small spatial reference object. Animal paths were triangulated from mobile camera positions obtained from a modified version of ORB_SLAM2, an open-source visual simultaneous localization and mapping software package. In addition to path calculation, this process provided a virtual three-dimensional surface approximation to the environment from which path to environment distances can be quantified. PATMOS can also fit a tranquil water’s surface to an analytic plane if there are a sufficient number of visible objects intersecting the water’s surface and can track objects over the water’s surfaces with a single camera by measuring the object with its reflection. This technology was highly portable, could follow moving animals, and gave comparable spatial and temporal resolutions to fixed camera systems that use commercial cameras. An investigation of falling objects yielded a gravitational constant measurement of 978 ± 40 cm s−2. I demonstrated PATMOS’s utility in terrestrial and aquatic environments by quantifying dragonfly flight characteristics and the inter-spatial distances between substrate and damselfish.