Recovering of 3D footwear impressions from sandy substrates: technical note on the contribution of SfM photogrammetry.

Abstract

Three-dimensional footwear impressions are often left at crime scenes, particularly in areas of dry sandy substrates common on footpaths, in roadside gutters and on waste ground. Loose fine sandy substrates can preserve remarkable levels of detail that can allow for the comparison of characteristics from wear and use of the shoe, beyond the consideration of class characteristics. A Crime Scene Investigator has a range of options at their disposal for the recovery of such an impression from casting through to 2D photography. Here we illustrate the use of SfM photogrammetry in the recovery of these sometimes ‘difficult to cast’ impressions. Our aim here is not to evaluate such methods in detail but simply draw the attention of CSIs to this potential. We do this via a series of different scenarios which illustrate the potential of SfM photogrammetry to provide a superior recovery method for sandy substrates. Given further evaluation and future evaluation of SfM methods we argue that it provides a potential complimentary recovery technique expanding the range of options available for loose, dry substrates.