3D-modeling of an experimenal wound channel caused by a piercing-cutting object with bilateral blade grinding

The research deals with the possibility to use up-to-date methods of 3D-modeling for diagnostics of piercing-cutting objects causing injuries with bilateral blade grinding. A virtual element of the wound channel is shown to be printed on 3D-printer and given to investigating bodies in order to increase the effective and objective search of a traumatic instrument.  Aim of the work. To apply the method of photogrammetry with further 3D-modeling of the wound channel formed by a piercing-cutting object with bilateral blade grinding for further examination of its morphological peculiarities and receiving its linear size with high accuracy in the space of graphics editor «3DsMax». Materials and methods. Fifteen experimental wound channels were made by means of alginate impression mass with rubber-like effect «Hydrogum 5» (firm «Zhermack», Italy), which becomes hard rapidly, remains elastic after polymerization, allows impresses to be obtained with an extremely smooth surface, most accurately preserves and reproduces characteristics of an immersed blade of the knife examined. To make experimental injury a piercing-cutting object was used – a knife with bilateral grinding of the blade 6,16 cm long, 2,6 cm wide in the base of the blade, and the blade in its middle part 0,3 cm thick. These sizes of the piercing-cutting instrument were obtained by means of sliding calipers with the error ±0,03-0,15 cm. The wound channel obtained was divided into fragments with a pitch about 3,5 cm. Every fragment of the wound channel was contrasted with a dye using 1 % brilliant green alcohol solution. All the fragments of the wound channel were opened parallel to its length and were placed on a rotary table located in a light cube to provide adequate illumination and photos were taken.  The digital camera SONY RX 10 II was used for shooting. The object of shooting was labeled with a number, a fragment of a plotting scale 1,0 cm long was placed on it to calibrate the scale and control the sizes of the object examined in computer programs. The photos obtained in JPEG format were loaded into the computer program «Agisoft Photoscan», and 3D-textured models of a wound channel fragment were created in it. The model obtained and the texture was exported in «OBJ» format. The next stage of the work was to transfer 3D-models obtained into the graphic space of «3DsMax» program, where the scale of the model was calibrated. After that the wound channel was reconstructed in the graphics editor by means of 3D models of the wound channel fragments. Results. To compare differences between classical and new methods of examination at first linear dimensions of injuries were measured by means of a ruler. The depth of the wound channel was obtained consisting of two fragments according to the method of measuring the wound channel depth in the dead body by means of joining of its separate parts due to immersion and passing the blade in the victim’s body (in the skin, subcutaneous tissue with muscles, in the wall of the cavity and inside of it, in the internal organ and other anatomical structures). The width and length of the wound channel on various levels of immersion were registered in the similar way, which is an important diagnostic component during forensic expertise in case of piercing-cutting injuries. The next stage in our research was to examine and get linear dimensions of injuries by means of up-to-date technologies using 3D-models with the help of the graphics editor «3DsMax». In this case the computer program enabled to get the above results with a higher accuracy to 0.001 cm. Conclusions. The results obtained are indicative of high information value of the three dimensional methods to identify a traumatic piercing-cutting object by means of a spatial reconstruction of the wound channel fragments, which provides high accuracy in solving applied tasks in modern forensic practice and criminal law science. The method with the use of the graphics editor «3ds max» allows retrospective diagnostics of the wound channel fragments to be obtained followed by further comparison with an expected traumatic object.