Abstract
This paper examines the reliability of Structure from Motion (SfM) photogrammetry as a tool in the capture of forensic footwear marks. This is applicable to photogrammetry freeware DigTrace but is equally relevant to other SfM solutions. SfM simply requires a digital camera, a scale bar, and a selection of oblique photographs of the trace in question taken at the scene. The output is a digital three-dimensional point cloud of the surface and any plastic trace thereon. The first section of this paper examines the reliability of photogrammetry to capture the same data when repeatedly used on one impression, while the second part assesses the impact of varying cameras. Using cloud to cloud comparisons that measure the distance between two-point clouds, we assess the variability between models. The results highlight how little variability is evident and therefore speak to the accuracy and consistency of such techniques in the capture of three-dimensional traces. Using this method, 3D footwear impressions can, in many substrates, be collected with a repeatability of 97% with any variation between models less than ~0.5 mm.
Highlights
This paper examines the reliability of Structure from Motion (SfM) photogrammetry as a tool in the capture of forensic footwear marks
The aim of this paper is to provide an assessment of the reliability and reproducibility of small-scale 3D capture methods involving structure from motion (SfM) photogrammetry
We evaluate the reliability of Structure from Motion (SfM) photogrammetry in capturing footwear evidence
Summary
This paper examines the reliability of Structure from Motion (SfM) photogrammetry as a tool in the capture of forensic footwear marks. The results highlight how little variability is evident and speak to the accuracy and consistency of such techniques in the capture of three-dimensional traces Using this method, 3D footwear impressions can, in many substrates, be collected with a repeatability of 97% with any variation between models less than ~0.5 mm. While often neglected in favor of other lines of forensic data, the analysis of footwear marks is undergoing a minor revolution in terms of potential scene capture methods This revolves around the application of small-scale (close-up) photogrammetry to capture 3D models, allowing rapid capture, visualization and numerical analysis of 3D traces. The use of photogrammetry in other areas of forensic practice highlight the perceived value and general feelings of the community regarding the technique; regarding levels
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