# Technological Development and Application of Photo and Video Theodolites
## 2 Technological Development
### Development from 1991-2000  
Available prototypes of video theodolites (Figure 6) in the 1990s encouraged intensive research on their application with high degrees of automation. Equipped with motors, video theodolites made it possible to increase the dynamism of computer-controlled measurements, turning a video theodolite into a robot [33]. Built-in sensors provided a wealth of data that demanded to be processed meaningfully to obtain the necessary information. Electronic reading of directions and lengths was around for a long time, but the processing of data obtained using built-in cameras was still in its initial stages. The application of digital image processing methods and computer vision was investigated by the academic community. Initial research focused on detecting artificial targets and accurate aiming with the help of cameras [34]. Figure 7: Geodimeter model 4000, i.e., the first “One-Man-System” in the world that required only one expert to operate it [22]. Aiming at and measuring unsignalized targets proved to be a special challenge [35]. To achieve this, solutions based on artificial intelligence were developed [36]. Until then, the expert/operator was in charge of sighting and deciding on the characteristic points to be measured. By implementing this knowledge into software solutions, artificial intelligence was applied, and expert systems were developed. Initially, development was limited to smaller and simpler processes that occurred in theodolite measurements [37]. Special attention was paid to the necessary sharpening of the image by developing autofocus algorithms [35; 37]. The developed processes and procedures were later implemented in commercial solutions of instrument manufacturers. This freed observers from repetitive operations, whereby they could now focus on more complex tasks. By automating the measurements, the level of achieved accuracy was increased. Computer-aided measurements and data processing provided greater accuracy than could be achieved visually by the observer. The developed systems could be applied to measurements in the industry. It was no longer necessary to bring the object to the measurement place since the system could be transported. External control of the developed systems allowed measuring objects at hazardous places. Since unsignalized targets could be targeted, measuring of inaccessible objects also became possible. At the very beginning of this epoch, in 1991, the automatic measuring system TOPOMAT was developed in Zurich. In collaboration with Wild, it was upgraded with a CCD image sensor to detect the target [22]. Its main features were that it could work independently, automatically, or via a controller. Other functions were also available via the controller, such as activation, deactivation, and change of measurement method [38]. GEOROOT and TOPOMAT had encouraged the development of commercial tracking TS. The transition from the 1980s to the 1990s was also marked by the development of the ATR function, which enabled the further development of IATS instruments. In 1991, Topcon presented its first motorized, auto-tracking total station AP-S1. In 1993, Topcon released its successor called model AP-L1, and 1996 saw the emergence of the new model AP-L1A, the so-called \"one-person surveying system\" [39]. This RTS differed from the instruments and developments presented before in that the fine aiming, similar to the structure of a television image, worked with line-deflecting optical elements (AO device) and could, thus, evaluate an image of the reflector illuminated by the instrument [40]. This system worked in conjunction with radio communication, a handheld data collector, and TDS Survey Pro Software. It produced a unique surveying system that enabled all field surveying tasks to be carried out by one expert working on their own.