Preserving the impossible: conservation of soft-sediment hominin footprint sites and strategies for three-dimensional digital data capture.

Human footprints provide some of the most publically emotive and tangible evidence of our ancestors. To the scientific community they provide evidence of stature, presence, behaviour and in the case of early hominins potential evidence with respect to the evolution of gait. While rare in the geological record the number of footprint sites has increased in recent years along with the analytical tools available for their study. Many of these sites are at risk from rapid erosion, including the Ileret footprints in northern Kenya which are second only in age to those at Laetoli (Tanzania). Unlithified, soft-sediment footprint sites such these pose a significant geoconservation challenge. In the first part of this paper conservation and preservation options are explored leading to the conclusion that to 'record and digitally rescue' provides the only viable approach. Key to such strategies is the increasing availability of three-dimensional data capture either via optical laser scanning and/or digital photogrammetry. Within the discipline there is a developing schism between those that favour one approach over the other and a requirement from geoconservationists and the scientific community for some form of objective appraisal of these alternatives is necessary. Consequently in the second part of this paper we evaluate these alternative approaches and the role they can play in a 'record and digitally rescue' conservation strategy. Using modern footprint data, digital models created via optical laser scanning are compared to those generated by state-of-the-art photogrammetry. Both methods give comparable although subtly different results. This data is evaluated alongside a review of field deployment issues to provide guidance to the community with respect to the factors which need to be considered in digital conservation of human/hominin footprints

Technological innovation in the recovery and analysis of 3D forensic footwear evidence: Structure from motion (SfM) photogrammetry

The recovery of three-dimensional footwear impressions at crime scenes can be a challenge but can also yield important investigative data. Traditional methods involve casting 3D impressions but these methods have limitations: the trace is usually destroyed during capture; the process can be time consuming, with a risk of failure; and the resultant cast is bulky and therefore difficult to share and store. The use of Structure from Motion (SfM) photogrammetry has been used widely to capture fossil footprints in the geological record and while there is a small body of work advocating its use in forensic practice the full potential of this technique has yet to be realised in an operational context. The availability of affordable software is one limiting factor and here we report the availability of a bespoke freeware for SfM recovery and subsequent analysis of for footwear evidence (DigTrace). Our aim here is not to provide a rigorous comparison of SfM methods to other recovery methods, but more to illustrate the potential while also documenting the typical workflows and potential errors associated with an SfM based approach. By doing so we hope to encourage further research, experimentation and ultimately adoption by practitioners

Technological innovations in the collection and analysis of three-dimensional footwear impression evidence.

The development of digital 3D trace recovery in the fields of geology and archaeology has highlighted transferable methods that could be used for the recovery of 3D footwear impressions under the umbrella of forensic science. This project uses a portfolio of experiments and case studies to explore the veracity and application of SfM Photogrammetry (i.e., DigTrace) within forensic footwear. This portfolio-based research includes published papers integrated into conventional chapters. A method of comparing the accuracy and precision of different measurement methods is developed and introduced and gives a comparative view of multiple recovery techniques. A range of simulated crime scene and laboratory-controlled experiments have been conducted to compare different recovery methods such as casting, photography and SfM photogrammetry. These have been compared for accuracy, practicality and effectiveness. In addition, a range of common and lesser common footwear bearing substrates have been compared using SfM as well as other methods. One of the key findings shows that DigTrace SfM photogrammetry software reliably produces accurate forensic results, regardless of the camera used for initial photography and in a multitude of environments. This includes but is not limited to, soil, sand, snow, and other less obvious substrates such as food items, household items and in particular carpet. The thesis also shows that SfM photogrammetry provides a superior solution in the recovery of ‘difficult to cast’ footwear impressions. This finding allows for 3D recovery of impressions that would otherwise have only been photographed in 2D. More generally this project shows that 3D recovery is preferential to 2D and aids in the identification of individual characteristics and subsequent positive analysis. Overall, the thesis concludes that SfM photogrammetry is a viable and accurate solution for the recovery of 3D footwear impressions both as an alternative and replacement to 2D photography and conventional 3D casting. SfM 3D recovery provides increased visualisation of footwear evidence and individualising marks. Digital evidence obtained in this way integrates with the increasingly sophisticated search algorithms being used within the UK’s National Footwear Database and allows rapid file sharing, retrieval and evidence sharing. Moreover, the technique has significant cost saving in terms of time, equipment and resources. It is the author’s opinion, having consulted a wide audience of footwear examiners and crime scene employees, that this technique should, and can be, adopted quickly by forces in the UK and USA and disseminated for use