# Technological Development and Application of Photo and Video Theodolites
## 4 Application of the State-of-the-Art Video Theodolites--IATS in Monitoring
### Applications in Structural and Geo-Monitoring  
One of the first applications of IATS for structural monitoring was conducted by the Chair of Geodesy, TU Munich, for the measurement of dynamic displacements and natural frequencies of the Fatih Sultan Mehmet Bridge over the Bosporus waterway in Istanbul, Turkey. Using a self-developed IATS prototype consisting of a Leica TPS1201 RTS with an ocular replaced by a 5 MPx CMOS color camera, they managed to determine vertical displacements of up to 50 cm and the first six natural frequencies of 0.106 Hz, 0.132 Hz, 0.176 Hz, 0.209 Hz, 0.272 Hz, and 0.333 Hz of the bridge during daily traffic. The determined frequencies coincided with the known frequencies from previous examination tests [7]. Research conducted at the Institute of Engineering Geodesy and Measurement Systems, TU Graz, covered a variety of experimental studies and in situ measurements using IATS Leica MS50 and MS60. They were aimed at determining the natural frequencies of the Augarten and Pongratz-Moore-Steg footbridges over the river Mur in Graz, Austria. For reference measurements, they used three accelerometers which were oriented in the vertical direction, across and along the bridge. At Augarten bridge, using a Leica MS50 and instruments favorably placed along the longitudinal axis of the bridge [79], they managed to determine vertical displacements of up to 0.5 mm and a bridge frequency of 1.81 Hz using IATS (1.81 Hz using the accelerometer), which corresponded to a bridge natural frequency of 1.8 Hz [80]. At Pongratz-Moore-Steg bridge, using a Leica MS60 and instruments unfavorably placed along the transverse axis of the bridge [79], they managed to determine a bridge frequency of 2.5 Hz using IATS (2.5 Hz using the accelerometer) which corresponded to the step frequency of runners over the bridge. The displacements along the bridge axis (longitudinal and transverse) were too small to be resolved using the IATS placed in an unfavorable position, and they primarily depended on the reflectorless distance measurement accuracy of the IATS [79]. For geo-monitoring, the concept of using two IATS instruments for high-resolution, long-range stereo survey of georisk areas was investigated in the EU-FP7 project DE-MONTES, and the facts, objectives, results, and full report can be found in [81]. In the paper [82], the used methodology and a comparison of the main features with other terrestrial geodetic geo-monitoring methods were presented. The theoretically achievable accuracy of the measurement system was derived and verified using in situ data of a distant clay pit slope and simulated deformations. The deformations were simulated using movements of an artificial rock, a 1 m \(\times\) 1 m structured and textured plate, which was fixed by two ropes and shifted and rotated to varying degrees during the different epochs. It was shown that the stereo IATS concept could obtain higher precision in the determination of 3D displacements, i.e., deformations, than other systems with comparable sensors. With the use of the telescope camera and telescope magnification, the images could be used for long-range applications. Dense point clouds with high single-point accuracy, including information about their precision, were generated. The 3D displacement vectors could be derived automatically and their significance specified. These results may be used to directly determine the rigid body motions of objects and surface patches. Compared to terrestrial laser scanner (TLS) measurements, long distances with smaller footprints are possible using the IATS approach, and there is no need for reference points within the region of interest. The large magnification of the telescope camera and the ability to capture image bundles further lead to a higher point density in comparison to simple photogrammetry approaches.