# Technological Development and Application of Photo and Video Theodolites
## 2 Technological Development
### Development from 2001 until Today  
The forerunner of today's state-of-the-art commercial IATS systems was Topcon's model GPT-7000i from 2005 (Figure 8). Topcon integrated the camera into a TS, which created a new generation of video theodolites, named IATS. The instrument was equipped with two different VGA cameras. One camera was wide-angle with an FOV of 28\({}^{\circ}\)\(\times\) 22\({}^{\circ}\) and fixed focus, located on the telescope, allowing rotation to be synchronized and the field working area to be displayed. The second camera was coaxial, and it recorded the details of the terrain seen through the magnification of the telescope; thus, it included variable focus. It had an FOV that matched the telescope FOV (1\({}^{\circ}\)30\({}^{\prime}\)\(\times\) 1\({}^{\circ}\)30\({}^{\prime}\)) [41]. In 2007, Topcon introduced the successor of the first series model GPT-9000 Ai. The greatest technological development compared to the GPT-7000i was manifested as the possibility of automatic focusing of signal points and remote guidance by the controller, which eliminated the need for an observer, making it a so-called \"one-man station\". It was also the first RTS that enabled the taking of photographs and the possibility of scanning as a unique function within the IATS system. The instrument could scan up 20 points per second [42]. These types of IATS have been produced by Topcon for three generations and are known as Imaging Stations, with the latest model called IS3. Both cameras had an image sensor with a resolution of 1280 \(\times\) 1024 pixels, and they could also record video at 10 frames per second (fps), which could be transmitted to the station control screen or to the controller screen. Trimble introduced its first IATS in 2007, the model VX Spatial Station (Figure 8). It was basically an S6 model with added functionality of 3D scanning and digital imaging. VX delivered images that were accurately georeferenced. The instrument was equipped with a 3 MPx color camera, with fixed focus and an FOV of 16.5\({}^{\circ}\)\(\times\) 12.3\({}^{\circ}\). The camera was located on the telescope. This camera was later implemented in all total station models that Trimble released, including today's Trimble S9 series. The features of postprocessing photogrammetric analysis of calibrated images, 5 fps video recording, panoramic mosaic image, and overlap with measured data are known as \"Trimble Vision\". The VX Spatial Station was an RTS with MagDrive servo technology, involving an integrated servo/angle sensor electromagnetic direct drive in combination with added digital imaging and rudimentary scanning capabilities. The scanning function could scan 20 points per second with the ability to colorize scanned scenes based on recorded images [43]. In 2009, Pentax presented an RTS with integrated cameras into its instruments, known as Visio series model R-400 VDN. The camera was placed on the telescope, and a screen displaying captured images and video from the camera was also placed on the telescope above the ocular (Figure 8). The FOV was 8.8\({}^{\circ}\)\(\times\) 8.8\({}^{\circ}\), and it could record video at 10 fps [44]. Leica introduced its IATS instrument in 2010 called Viva; two models with overview cameras placed on the telescope were presented: Leica TS11 and Leica TS15 (Figure 8). Model TS15 was motorized using a servofocus drive with additional sensors for automatic and remote control, unlike TS11. The overview camera had an optical axis different from the optical axis of the telescope, which resulted in parallax; thus, the center of the optical axis of the telescope did not coincide with the center of the image sensor. The relative position of these two axes was determined by calibration at the time of its manufacturing. The effect of parallax could also be corrected by measuring the distance to the target.