In most situations, a single scan will not produce a complete mod

In most situations, a single scan will not produce a complete model of the subject. Multiple scans from different directions are therefore required to obtain information about each side of the subject. These scans have to be brought in a common reference system, a process that is usually called alignment or registration, and then merged to create a complete model [7]. Nowadays, laser scanner devices are frequently used for forensic investigation [2], since evidence gathered with laser scanning can be more compelling for juries and allow investigators to virtually ��revisit�� a crime scene.Close range photogrammetry allows the acquisition of information about physical objects through the process of recording, measuring, and interpreting photographic images. It may be used in any situation that requires the generation of accurate 3D data and is ideally suited to the survey and measurement of buildings and rooms. Usually, a detailed photogrammetric survey is not carried out immediately after the event, since it is a time-consuming procedure and requires the presence of a skilled technician. However, a post-event survey allows the generation of a map of the crime scene to be used as reference data.2.1. Sole footprint modelingIn order to have a 3D model of a specific sole footprint, required to correctly model human walk as clearly described in Section 4, a high-resolution scan should be acquired. Assuming the availability of the shoes worn by a suspect at the crime scene, a handheld high resolution triangulation scanner can be used in order to generate the model. The instrument used for the acquisition of the shoe sole is the Handyscan 3D produced by Creaform (Figure 2c); this scanner can acquire up to 25,000 points/second with a resolution of about 0.05 mm and an accuracy of 0.04 mm. High resolution 3D survey systems have long existed, especially for mechanical applications. Even if the different available solutions (laser distance measurements on controlled mechanical tables, stand-alone instruments, etc.) are based on different measuring principles, they show common technical problems, related to the stability of the acquisition reference systems during the survey or to the need to have direct access to the object.The instrument used belongs to a new generation of high resolution and precision scanners which have recently been introduced. With a direct survey in a 3D reference system materialized on the object, or nearby, these new instruments (the so-called third generation scanners) allow a complete surface of convex and concave objects to be scanned avoiding the necessity of moving the object from its natural location and without heavy instrumentation [8]. The basic idea of this instruments is very simple (it is a digital photogrammetric system), but the adopted solutions represent a true novelty from different points of view in the crime scene reconstruction field.