The methodology, based both on geomatic survey techniques and GIS analyses tools developed to achieve the aforesaid goals, requires:the availability of pictures taken by first aiders (law enforcement agents, forensic scientists, etc.), that provides information about the crime scene before items are moved or interfered with. Generally those pictures are acquired for record keeping purposes, focusing the attention on the semantic content and neglecting the geometric one, thus they are characterized by large geometric distortions that require an adequate modelling to be corrected;the availability of the shoes of the suspect (eventually of all the people whose movements on the crime scene have to be verified), to create a sole 3D model required as input data to reconstruct a specific sole footprint.

The availability of the real shoes is critical because particular sole consumption shapes may affect significantly shape and extent of the contact surface.A schema of the methodology developed by the authors is proposed in Figure 1, to allow the readers to better understand the structure of this paper and its most innovative parts.Figure 1.Schema of the developed methodology.2.?Reference data acquisitionIn order to correctly georeference all the images and data acquired at a crime scene by first aiders it is fundamental to have the sufficient number of 3D reference points characterized by high geometric accuracy.

These point can be used both as Ground Control Points (GCPs), required for the georeferencing procedures (see Section 3.1.2), Entinostat and as independent Check Points (CPs), useful for the evaluation of accuracy.

Generally this kind of data are obtained by means of surveying or phogrammetry. In the following chapters these techniques will be briefly described; they are often used jointly in order to have a redundant number of measurements, for two main reasons: crime scenes are not easily accessible in case of accidental data loss and the availability of redundant data allows one to evaluate the accuracy of the estimated coordinates.Surveying techniques help determine accurately the terrestrial or 3D space position of points and the distances and angles between them, using a total station instrument (Figure 2a) or a laser scanner (Figure 2b).

Figure 2.(a) Example of a total station (Leica TPS1200+ Total Station); (b) example of a 3D time of flight laser scanner (Riegl LMS-Z420i); (c) example of a 3D triangulation laser scanner (Creaform Handyscan 3D).A laser scanner is usually used to create AV-951 a point cloud of geometric samples on the surface of an object. These points can then be used to extrapolate the shape of the subject (a process called reconstruction).