## 4 Results
### Digital Oven 3D Models
#### 4.2.3 Comparison of SLS and SfM Technologies  
The collective parameters of digital 3D models of the furnace made in SLS and SfM technology are presented in Table 5.  
The results included in Table 5 show that the optimisation of the 3D model obtained from the SLS method, consisting in a 10-fold reduction of the mesh size and 4-fold reduction of the texture dimension, with a virtually invisible visual change of the object, resulted in a reduction of the total file size over 6.5 times. With regard to the digital model from the SfM method, the improvement in object visibility after smoothing resulted in an almost 2-fold increase in the.obj file size. It should be added that the size of this file is almost 3.5 times larger than the SLS file, and the appearance of this model is of lower quality anyway. Figure 16: 3D model with the texture of the dishes in the furnace: (**a**) original version, (**b**) after smoothing the surface. Figure 15: Three-dimensional model of the furnace obtained by the SfM method: (**a**) original version, (**b**) after smoothing the surface. Tables 6 and 7 present the time-consuming nature of data acquisition and processing when creating digital 3D models of a jug and a stove using the SfM and 3D SLS methods. Table 8 lists the costs of devices and software used in the SfM and 3D SLS methods. The analysis of the results in Table 6 concerning the generation of a 3D model of a small jug shows that the time taken by the SfM method is almost twice as long as that of the 3D SLS methods. If more photos were taken, the time would increase to about 3 times. Knowing that raw photos need to be pre-processed, time can be saved by generating a 3D model from these photos and cropping them can follow straight away. In the case of a large object--a furnace (Table 7), it can be seen that the SfM method is about 15 times less time-consuming than the 3D SLS methods. In the method, scanning a large, complex surface takes a long time, as opposed to taking photos. When photographing the furnace, there was no need to create a shooting station, and moreover, the furnace was positioned against the wall, so only one accessible side was photographed. All this meant that the shooting time was 4 times shorter than that of a small jug. The program generating a 3D model from photos requires approximately the same time to generate the model, regardless of whether the object in the photos is large or small. Initial processing of scans from the 3D SLS method, consisting in separating point clouds from each other, when information about reference points was lost in the scanning process, and their recording as separate \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **SfM/Meshroom Program** & **min** & **3D SLS/Artec Studio Professional 15 Program** & **min** \\ \hline Data Acquisition & & 12 & 5 \\ \hline \multirow{6}{*}{Data processing} & Making a 3D model from raw photos—an automated process & 20 & \\ \cline{2-3}  & Photo processing & 90 & \\ \cline{1-1}  & Making a 3D model from processed photos & 20 & \\ \cline{1-1}  & Smoothing the model in Blender & 8 & Optimising the 3D model mesh in Blender & 10 \\ \cline{1-1}  & Total & 150 & Total & 85 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Time-consuming production of the 3D model of the jug using the SfM and 3D SLS methods. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **SfM/Meshroom Program** & **min** & **3D SLS/Artec Studio Professional 15 Program** & **min** \\ \hline Data Acquisition & & 3 & 55 \\ \hline \multirow{3}{*}{Data processing} & Making a 3D model from raw photos—an automated process & 20 & Converting a point cloud into a 3D mesh model—manual process & 480 \\ \cline{1-1}  & Smoothing the model in Blender & 15 & Optimising the 3D model mesh in Blender & 15 \\ \cline{1-1}  & Total & 38 & Total & 550 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Time-consuming production of 3D models of the furnace using the SfM and 3D SLS methods.