## 4 Development of a VLBI Antenna Static Displacement Monitoring Program  
A program for monitoring the static displacement of the VLBI antenna's main reflector was developed. The user interface (UI) was configured with features such as camera initialization, display of captured images, input for image coordinates and ground control point coordinates, calculation of the interior and exterior orientation parameters, calculation of the 3D position coordinates, and storage of observation results. To develop the software, the C# programming language was used on the Microsoft Visual Studio 2008 platform (Redmond, WA, USA). When the camera setting list in Figure 9 is clicked, the camera is initialized for taking pictures of the VLBI antenna.  
Figure 10 shows a captured image and the image coordinates and ground control point coordinates for the feature points of the VLBI antenna surface, which will be used for calculating the interior and exterior orientation parameters.  
Figure 10: Operation screen of the VLBI antenna static displacement monitoring program.  
Figure 9: Camera initialization user interface.  
After the image coordinates and ground control point coordinates for the feature points of the VLBI antenna surface are entered, as shown in Figure 10, the steps for calculating orientation parameters for the stereo images proceed. Figure 11 shows final results of the interior and exterior orientation parameters for the left and right images.  
Figure 12 shows the calculated 3D position coordinates for the feature points on the VLBI antenna surface in the software. The 3D position coordinates were calculated using the image coordinates for the conjugate point representing the positions of the common points in the stereo images, and the precise interior and exterior orientation parameters that had been determined through the previously described calculation process. The 3D position coordinates for the conjugate point were calculated using four collinearity equations for the stereo images. Therefore, a total of four residuals were calculated for the 3D position coordinates determined using the least-squares method. The precision of the results was verified using the standard deviation of the residuals, as shown in Figure 12. The mean precision of the 3D position coordinates was 2 mm.  
However, the standard deviation calculation from the residuals produced a statistical evaluation of the theoretical precision of the 3D coordinates computed with the bundle adjustment. Therefore, to estimate the overall accuracy of the system, the positional accuracy was calculated by comparing the experimental results from this study with total station survey results.  
For the total station survey results used in this evaluation, the ground control point survey results for a total of 188 feature points on the VLBI antenna surface were used.  
Table 1 shows the statistical analysis comparing the 3D position coordinates calculated through this program and the total station survey results for the 188 conjugate points. In fact, both sets of measurements resulted in accuracies of \(\mathrm{X}=1.13\pm 3.02\) mm, \(\mathrm{Y}=-0.92\pm 3.35\) mm, \(\mathrm{Z}=-1.05\pm 3.67\) mm, thus showing a high degree of accuracy.  
Figure 11: Result screen for the initially calculated interior and exterior orientation parameters for the stereo images. (**a**) the final orientation results for the left image; (**b**) the final orientation results for the right image.