# Technological Development and Application of Photo and Video Theodolites
## 4 Application of the State-of-the-Art Video Theodolites--IATS in Monitoring
### Case Study  
In this section, we present our own experiment to contribute to the above-presented theoretical basis, along with conclusions reached regarding the potential benefits and possibilities of using IATS for structural monitoring. Because of the lack of a state-of-the-art IATS, as shown in Section 2.5, we developed our own IATS prototype consisting of a Leica TPS1201 RTS and a GoPro camera mounted on the ocular of the telescope (Figure 12, left). We designed an adapter for fitting the GoPro camera on the Leica TPS1201, made using a 3D printer. This offered the possibility to directly attach the camera to the ocular of the telescope of Leica TPS1201. Before conducting measurements, we performed a stability examination of the instrument's telescope in the laboratory using a fitted camera in vertical direction. The examination showed that there were no movements of the telescope. The IATS prototype offered the possibility to manage the camera using the smartphone GoPro application, while we could manage the instrument using a laptop. Thus, we did not have to touch the instrument or the camera, thereby ensuring its stability along the horizontal and vertical axes. Before conducting tests in the field, we performed another experiment in the laboratory where we tested the ability of the IATS prototype to determine predefined amplitudes with different frequencies using a multi-purpose universal testing machine intended for static and dynamic testing of mechanical properties of building materials and constructions. The test consisted of simulated amplitudes of \(\pm\)0.2, \(\pm\)0.5, \(\pm\)1.0, \(\pm\)2.0, and \(\pm\)5.0 mm at frequencies of 0.2, 0.5, 1.0, 2.0, and 5.0 Hz. We managed to determine all amplitudes and all frequencies, as partially presented in [83]. The conducted tests in the field were performed on the railway bridge Klostar after its reconstruction for the purpose of load testing (Figure 12, middle). Since the bridge did not have any characteristic points, i.e., unsignalized targets suitable for image processing and target identification between frames, we used predefined photo marks (Figure 12, right) for target detection between frames. The photo marks were four different circles with predefined diameters (5 mm, 10 mm, 15 mm, and 20 mm), as well as a predefined horizontal spacing between the circle centers of 40 mm and a vertical spacing of 20 mm, as shown in Figure 12 (right). The IATS prototype was placed at a distance of 28.519 m perpendicular to the longitudinal axis of the bridge in the middle of the bridge span (Figure 13). This way, we achieved the optimal position of the IATS prototype relative to the bridge for determination of the bridge's vertical displacements, since the longitudinal axis of the bridge was parallel to the image sensor. Using the instrument's telescope at 30\(\times\) magnification, the camera recorded a movie with the following settings: narrow FOV, 1920 \(\times\) 1080 px, ay 60 fps. With this setup, we achieved the smallest circle with 5 mm diameter and 15 pixels, i.e., one pixel corresponded to 0.333 mm for this case study setup in the field. We also used accelerometers for measuring the frequency response of the bridge. Figure 12: IATS prototype (**left**), railway bridge Klostar over the river Dobra (**middle**), and photo mark (**right**). Figure 13: IATS prototype setup in the field in relation to the bridge. Trains passed along the bridge at different speeds. In this study, we show the results from two tests, i.e., when the trains passed at 40 km/h and 60 km/h. For processing the recorded movie from the camera, we developed an algorithm in MATLAB. The algorithm performed several steps. First, the movie format was converted into frames, whereby each image represented one measuring epoch. Then, the image was transformed into am orthogonal projection according to the known azimuth and zenith angle of the IATS prototype to the longitudinal axis of the bridge, i.e., to the position of the photo mark.