## 2 Materials and Methods
### Development of Procedures for Verifying Geometrical Accuracy
To obtain the complete geometry of a part of the pelvic model made as a single piece, measuring it in two orientations was necessary, as simultaneously measuring the model's surfaces in one position was impossible. Three geometry scans were taken at each model orientation, requiring six scans to obtain the model's geometry fully. Attempts to measure with fewer scans were unsuccessful in fully reconstructing a part of the pelvic model geometry. The two-point clouds obtained in positions one and two were aligned. First, an initial alignment was carried out based on feature point markers placed on the model. The final alignment was obtained using the best-fit method. This iterative process minimizes the square of the distance between the nominal and measured data to achieve convergence in the solution. The iterative process continued until the alignment of point clouds reached a value of \begin{table}
\begin{tabular}{c c} \hline
**Parameters** & **Value** \\ \hline Stripe width (Y) & 100 mm \\ Measuring range (Z) & 100 mm \\ Stand-off & 100 mm \\ Min. point resolution & 0.050 mm \\ Max. data rate & 150 Hz \\ Laser power Class 2 & 660 nm \\ \hline \end{tabular}
\end{table} 
Table 1: Established measurement parameters for the measuring arm-laser head system. 0.005 mm. The result was a complete representation of the model surface. When scanning three pelvic fragments, measurements were carried out at two different orientations of the models. However, it was sufficient to perform three scans in each model orientation to visualize the complete geometry of the models. Subsequently, the individual scans were adjusted similarly to a part of the pelvis model manufactured in one piece. The entire process is illustrated in Figure 4.  
Structured light methods can obtain information about the entire area of a measured model using [PERSON]'s stripe projection. The Atos II Triple Scan is a measurement system based on this method [45; 46; 47]. It comprises a stand with a measuring head, a projector, and two 5,000,000-pixel resolution cameras. The system includes a rotary table and a computer system for processing measurement data. The scanner uses triangulation to capture information about the position of points in space. The measurement result is a three-dimensional representation of the scanned geometry saved in STL format. During the calibration process of the Atos II Triple Scan system, three tests were conducted under the VDI/VDE 2634 standard [48]. Ceramic spheres were the standard for the optical head (Ps) test. The deviation between the measured diameter of the sphere and the calibrated value was determined using the least squares method, as per Equation (4). \[P_{s}=D_{measured}-D_{calibrated}, \tag{4}\]  
A standard was used to study the distance error (SD), in which two ceramic spheres were placed at a known distance. The error was calculated as the difference between the  
Figure 4: Developed geometry measurement procedure using a measuring arm-laser head system on the example of models manufactured for the surgery of patient no.1. estimated and calibrated distance between the centers of the two spheres. The distance was determined as the average of the measured values obtained from multiple soundings and calculated using Equation (5). \[SD=L_{measured}-L_{calibrated}, \tag{5}\]  
A ceramic rectangular plate standard was used to check the flatness error, which was determined using the least squares method. After calibrating the equipment, we tested the manufactured models. The entire process is illustrated in Figure 5.  
For methods using structured light, the resolution of the point cloud that reconstructs the measured geometry depends on various factors, including the measurement area's size and the measurement head's technical parameters (Table 2).