# Technological Development and Application of Photo and Video Theodolites
## 2 Technological Development
### Development from 1941-1980  
After World War II, a theodolite named Electronic Eye (Figure 4, left) was developed at the Institute of Applied Geodesy in Frankfurt for automated aiming based on the difference  
Figure 3: Wild photo theodolites P30 (**left**) and FT9 (**right**) [20]. Figure 2: Photo theodolite from Italian army (**left**), Finsterwalder photo theodolite (**middle**), and Pulfrich photo theodolite (**right**) [18]. of two currents in a photoelectric cell. This method was further developed to enable bearing accuracies of 1'' as a mean of six sets of directions in the late 1950s [21]. Testing gave very good results; thus, the company Askania produced a modified theodolite based on Electronic Eye--the Askania Tracking System (Figure 4, right). While Electronic Eye could only measure static targets, the Askania Tracking System already had the ability to register the orbit of moving objects (aircraft or missile) during WW2. The Askania Tracking System was used as a tracking system from the late 1950s to 1973 [23]. Later, the type of theodolite shown on the left of Figure began to be produced in Switzerland under the name Contraves EOTS (electro-optical tracking system) and was later produced in China [22]. The instrument, called a cinetheodolite, was used to record important data during testing of missiles and aircrafts, as well as other experimental weapon systems. Ballistic cameras that were used in satellite geodesy very often had integrated CCD image sensors for video recording, and they can also be structurally considered as video theodolites [22]. With the aim of recording the landing of aircraft using the instrument, in 1972, a portable Minilir system was developed in Paris [22]. The system was developed as part of the internal research project SAT (Societe Anonyme de Telecommunications), and it was not only a geodetic advancement but also a military tool for automatic monitoring of infrared radiation, such as aircraft and missile exhausts. The aiming was based on the detection of aircraft headlights using a very sensitive infrared sensor that recorded the frequency and phase-modulated signal. This instrument has been used since the 1980s in combination with various distance-meters such as the IBEO Fennel electronic distance-meter (EDM) or the AGA Geodimeter-112 EDM. Depending on which EDM was in place, the instrument was referred to as AGA-Minilir (Figure 5, middle) or Fennel-Minilir. This instrument was used as early as 1980 in the Dutch delta project for the coastal navigation of transport ships. In combination with a film camera, the system became known as a cinetheodolite, which was used on launch sites Kourou (Guiana Space Centre) and Cape Canaveral. In civil use, Minilir has been used for the calibration of instrument landing systems [24]. Minilir was followed, in 1983, by the Krupp Atlas-Elektronik instrument known as Polarfix (Figure 5, right). The laser measuring principle for short-range high-accuracy dynamic survey applications was the basis of Polarfix. Polarfix had several advantages and improvements compared to the Minilir system. While Minilir required a heat source to find the target, Polarfix only needed a passive reflective prism to achieve target tracking. The vertical circuit was automatically compensated for, and the instrument could be operated on a 12 V source instead of a 220 V source, which allowed the use of batteries. Its weight and volume were twofold lower compared to Minilir. The system provided polar coordinates  
Figure 4: Electronic Eye from the Frankfurt Institute of Applied Geodesy (**left**) and the Askania Tracking System (**right**) [21; 22]. for position fixing, incorporated a fully automatic operator-free tracking function, and ensured range/azimuth fixing to 10 cm + 5 cm/km accuracy from a single shore-station linked to shipborne telemetry and beam reflector facilities. The operating range depended on weather and other factors, but its typical basic range was just under 3 km, which could be extended to 5 km or more.