The Forensic Utility of Photogrammetry in Surface Scene Documentation

Abstract

Outdoor crime scene documentation needs to be accurate and precise to preserve evidence. Photogrammetry is a potential option. Structure from Motion (SfM) processes photographs into 3D models. As commercial software does not disclose this process, this documentation technique could be legally inappropriate. A potential solution to this problem is open-source software. A series of mock outdoor crime scenes were documented using SfM and total station mapping. Ten large surface scatter scenes containing plastic human remains and personal objects were laid out in 10 × 10 m units in a New England forested environment. The small surface scatter scenes consisted of a pig (Sus scrofa) mandible placed in different environments. The resulting models were built using PhotoScan by AgiSoft and MicMac by IGN. Accuracy was measured by the amount of variance in fixed-datum measurements, whereas visual qualitywas determined by comparison.
 The average total variance in fixed-datum lengths for six of the ten scenes was below 0.635 cm. The maximum differences in measurement between the total station and software measurements were 0.0917 m (PhotoScan) and 0.178 m (MicMac). Comparative histograms had low standard deviations and mean distances between points. Conditions such as light, ground foliage and topography affect model quality. This research shows that SfM has the potential to be a rapid, accurate and low-cost resource, but there are limitations that must be considered.