3D-technologies in forensic examination

Polyakova Anastasiya Vasil'evna ORCID: 0000-0002-0256-2432 Senior lecturer, Department of Forensic science, National Research Lobachevsky State University of Nizhny Novgorod 603105, Russia, Nizhny Novgorod region, Nizhny Novgorod, Boris Panin str., 5/5 anastasia.poliakova811@yandex.ru

Introduction

Scientific and technological progress brings a lot of new things to modern criminal proceedings, making the process of disclosure and investigation of crimes more technologically advanced. In the context of the industrial revolution 4.0, advanced technologies that will further serve as a vector for the development of forensic examination, according to A.V. Kokin, are "3D printing, artificial intelligence, biotechnologies, robots" ^{[1, p. 33]}. These technologies can fairly be supplemented with three-dimensional modeling and visualization, which make it possible to present objects of forensic examination in digital form in the form of 3D models.

An invaluable advantage of three-dimensional technologies is, first of all, the possibility of fixing the original appearance of objects subject to changes, whether it is the situation of the scene itself, or individual traces that may be affected by adverse weather conditions, their short duration of existence, the actions of the participants of the investigative task force, the applied technical and forensic means and methods of collection. Recording information in electronic form allows you to return to the analysis of the seized traces and the situation of the scene at any time of the preliminary investigation, to demonstrate them during the court session to increase the visibility of the evidence study.

The study of foreign experience in the use of three-dimensional modeling and visualization systems in the investigation and consideration of criminal cases indicates the need for their use in conditions of non-obviousness of the event ^[2], difficulties in direct investigation of complex mechanisms and events ^[3], integration of the information collected in the case for the reconstruction of the event ^[4].

The main part

Technologies for obtaining three-dimensional models can be represented as the following system: 3D scanning technologies, creating models in 3D editors, in computer-aided design systems (hereinafter referred to as CAD) and obtaining models from photographs and video frames by photogrammetry.

Three-dimensional scanning is a technology for obtaining a three-dimensional model of an object by collecting data on its shape, appearance and geometric parameters, and converting them into digital form. 3D scanners are a device for fixing a set of points reflecting the geometry of an object and subsequent modeling. The result of this digitization of the object is a three-dimensional model, which can later be imported into the necessary software and examined in accordance with the tasks of expert research.

Depending on the principle of operation, 3D scanners are divided into contact, in which direct contact of the scanning device (for example, a probe) with the original object is necessary to obtain a three-dimensional model, and non-contact, in which scanning is carried out by registering light reflected from the surface of the object ^{[5, pp. 23-24]}. The latter type of scanners is the most common. Based on the presence of a radiation source in the device, 3D scanners distinguish between active (the source is built into the scanner) and passive (uses either natural lighting conditions or a third-party artificial light source, the light of various lamps) ^{[6, p. 62]}. By the nature of the illumination source, 3D scanners are divided into laser scanners, emit a laser beam onto the surface of an object and fix reflected rays using a sensor, and structured light scanners, which project a light grid onto the object and also fix reflected rays ^[7].

Three-dimensional scanning technologies have proven themselves on the positive side when fixing tracological objects ^[8], the situation of road accidents ^[9].

         Universal 3D editors and 3D modeling programs, for example, Maya products, Autodesk 3DS Max, Blender 3D, Cinema 4D, ZBrush, etc., have huge opportunities for three-dimensional modeling and animation.

                Object modeling includes the following categories: geometry (model construction techniques); materials (information about the visual properties of models); light sources (setting the direction and power of illumination); virtual cameras (selecting the point and angle of projection); forces and impacts (animation), additional effects, visualization (rendering).

                   In 3D modeling programs, there are several different types of constructing the geometry of a three-dimensional model: polygonal modeling, which is based on creating polygon surfaces that consist of vertices, edges and faces; spline modeling - creating a model through smooth curves (splines); using B–splines - a type of modeling designed to create smooth shapes and models based on a special mathematical apparatus; sculpting – modeling a model by deforming a polygonal grid using various brushes ^{[10, p. 6-8]}. Primitives (geometric shapes), flat surfaces, and arbitrarily defined surfaces can act as initial data for modeling.

         At the stage of texturing the surface of the model, they get the appearance of real materials. In any 3D modeling program, there is a so-called Materials Editor, which contains both ready-made sets of materials and the tools with which they are created.  In the process of creating materials, texture maps are used, which are bitmap images of real objects. These maps are used in obtaining the relief and volume of the surface of the model based on the creation of a difference in the brightness of colors.

         The creation, direction and adjustment of virtual light sources are designed to emphasize the properties of the scene made as a result of modeling and the use of materials.

         One of the most important tasks of three-dimensional modeling is to obtain a realistic final image. Visualization is the final stage of working on the model. At this stage, the model turns into a form accessible to visual perception, which is called rendering. Only at this stage is visualization of all the properties of the object's materials, light sources, and environmental effects that were introduced into the scene ^{[10, p.11]}.

         The use of such editors for the needs of forensic examination is possible, both by importing ready-made three-dimensional models obtained using other methods into the program, and recreating the circumstances of the event from scratch using software tools. A forensic expert can analyze the mechanism of trace formation and its conditions, as well as make a comparative study of the trace model, the experimental sample and the trace-forming object itself ^[11].

         Computer-aided design (CAD) systems also belong to the software of three-dimensional modeling, which allow for the description of an object, the algorithm of its functioning, programming of production using a computer ^{[12, p.5]}. Moreover, these programs work not only with 3D models, but also with two-dimensional images (drawings, design documentation). Among the computer-aided design systems, the most common are COMPASS-3D, AutoCAD, SolidWorks, Autodesk Inventor, ArchiCAD, nanoCAD.

         One of the most popular ways to obtain three-dimensional models is photogrammetry, which is based on obtaining a series of overlapping photographic images or video frames. Photogrammetry allows you to determine from images, frames the shape of an object, its dimensions, spatial position in a given coordinate system, as well as its area, volume, changes in values after a given time interval ^{[13, p.6.]}. Among the photogrammetry software on a PC, Autodesk ReCap Pro, Autodesk Fusion360, Agisoft Metashape, Context are well-known Capture, Meshroom, Pix4D, 3DF Zephyr, COLMAP, there are also applications for building models on smartphones: Qlone, Scann3D, ScandyPro, Sony 3DCreator, Pix4Dcatch: 3D scanner, etc.

         The technology of three-dimensional photogrammetry is the closest to the activities of a specialist and an expert, since photofixation is the main method of fixing information about objects together with logging. With the correct application of methods and techniques of forensic photography, it is possible to preserve information about the external structure of objects that may change or collapse in the future, as well as sending them in electronic form for expert research.

Three-dimensional models obtained as a result of any of these technologies can be further printed on a 3D printer for presentation in physical form. Such full-scale models can be examined by an expert during the forensic examination, used as a full-scale sample in the collection of forensic objects, presented in the courtroom to illustrate the circumstances of the event under investigation ^[14].

In addition, the considered methods of constructing models can be used in a complex to reconstruct the event that occurred ^[15]. Three-dimensional reconstructions allow integrating the data obtained during various investigative actions into a single system that will allow you to build and verify investigative versions, establish objective circumstances of the case under investigation.

The use of three-dimensional models is also seen in the formation of both electronic and full-scale collections of forensic objects (for example, bullet holes, shoe prints, hacking tools, traces of teeth and dental apparatus, etc.). Moreover, the accumulation of information is possible by saving models obtained using universal technical means and software, and by maintaining data banks in automated systems of various kinds and types of forensic examinations. For example, in automated ballistic identification systems in which 3D modeling mode is implemented ^[16].

Conclusion

The existing technologies for obtaining three-dimensional models have an extensive set of technical tools and software for universal and specialized purposes that can be used in forensic activities. The subject of the model construction chooses the method based on the nature of the object of fixation, the set goal and objectives, as well as the technical capabilities of the forensic unit.

The main directions of application of 3D technologies in legal proceedings can be represented as follows: fixation, seizure and preservation of information about the traces of a crime, the situation of the scene of the incident during investigative actions, during the production of forensic examination; production of identification and diagnostic expert studies; three-dimensional reconstruction of the event under investigation; 3D printing of physical evidence; conducting forensic accounting; use in the training and advanced training of expert personnel.