## 3 Procedure for Forensic Facial Soft Tissue Reconstruction in Detail
### Digitization of the Mortal Remains
#### 3.2.2 Photogrammetric Images and Modeling of the Victim in Case 2  
Photogrammetric images and photogrammetry itself are based on non-contact measurement methods and evaluation procedures that indirectly determine the position and shape of an object from photographs by measuring the image. This procedure is known in the literature as the \"photogrammetric method\" [59]. The use of specially developed algorithms, such as the SIFT algorithm (SIFT stands for scale-invariant feature transform), enables the calculation of 3D models of the depicted objects from overlapping photogrammetric images. In Case 2, the skull, or more precisely, the cranium, skullcap, and lower jaw, were positioned on a turntable (company: stageonair, Penzing, Germany; [60]) and photographed 90 times, i.e., every 4\({}^{\circ}\), with reference marks from three different perspectives using three Nikon D7100 and D7500 SLR cameras with simultaneous shutter release (Nikon Corporation, Tokyo, Japan; a total of 270 images per run, i.e., 90 images per SLR camera). Three NG-220A continuous light studio lights from NANGUANG (Guangdong Nanguang Photo&Video Systems Co., Ltd., Dongguan, China) were used as a light source, some of which were fitted with softboxes to ensure homogeneous illumination. The principle of photogrammetry and the test setup are shown in Figure 5. The photogrammetric images of the skull, more precisely the cranium, skullcap, and mandible, are shown in Figure 6.  
Figure 4: Volume model from the CT data of Case 1 in the Blender software application. The display of the volume model, calculated from the CT data in the Blender software application, is shown with artifacts (**A**) and after the post-processing steps (**B**). The latter model formed the basis for the actual soft tissue reconstruction of the face. Figure 3: Calculation of the volume model from the CT data of Case 1 in the software application InVesalius [37]. Display of the three slices: axial (**A**), sagittal (**B**), and coronal (**C**), as well as the calculated volume model (**D**) of the skull in the software application InVesalius using version 3.1.1. Possible artifacts were removed in post-processing steps. The photogrammetric images of the bony structures of the skull were processed into 3D models using the open-source software Meshroom (Version 2021.1.0) [38]. The basis for the 3D modeling was 270 photographs (90 images per SLR camera) for the cranium, skullcap, and mandible, respectively. The primary processing steps involved the extraction of image features, the alignment of the overlapping images, the calculation of the point cloud, the meshing of the point clouds, and the subsequent texturing of the calculated 3D models. Following data processing, a 3D model was generated for each of the images of the cranium, the skull, and the mandible. These were then combined into an overall model in the Blender software application. An overview of the calculated individual models and the combined model is presented in Figure 7.  
Figure 5: Principle of photogrammetry and experimental setup for photogrammetric photographs of the skull of the victim in Case 2. (**A\({}_{1}\)A\({}_{2}\)**) The three-dimensional structure of an object can be calculated using appropriate software applications based on overlapping photographs from different perspectives. The photographs themselves were taken on test setups, as shown in sub-figures (**B**,**C**). (**B**,**C**) show the positioning of the skull on a turntable. Three Nikon D7100 and D7500 single-lens reflex cameras with a simultaneous shutter release and three NG-220A continuous light studio lamps from NANGUANG were employed for the photographic sessions. The skull was captured a total of 90 times, with one image being taken at a 4\({}^{\circ}\) angle. Consequently, 270 images were generated per session (90 images per camera). Figure 6: Exemplary photogrammetric images of the skull of the victim in Case 2, more precisely, the cranium, skullcap, and lower jaw.