PHOTO-TACHEOMETRY AND INTELLIGENT SCANNING. AN ALTERNATIVE TO 3D-LASER SCANNING (2005)

The method of photo-tacheometry is based on tacheometry as well as on elements of photogrammetry. Its basic hardware components are an intelligent tacheometer and a digital camera. An intelligent tacheometer is a motor-driven total station capable of reflectorless measuring, which is controlled and directed via a computer-notebook. This combination enables the development of control circuits and other “intelligent” control mechanisms that are based on the process of setting out. Intelligent tacheometry has several major advantages over traditional manually controlled electronic tacheometry. In combination with an image from the digital camera there are some more benefits concerning a) the field of documentation (i.e. by online superpositioning an image with other graphic information), b) the control of the instrument and c) the use of a photo for visualization purposes on site - detailed recording and control are possible as well as quick construction of photorealistic models. The most important functions of photo-tacheometry are explained, the advantages are shown and the differences between traditional tacheometry, intelligent tacheometry and laser scanning are discussed in detail. The user may decide if and where photo-tacheometry offers an actual advantage over laser scanning. 1. SOME NECESSARY DEFINITIONS Photo-tacheometry, intelligent scanning, intelligent tacheometry are keywords that arose in the course of the last two years. Their common basis is the well known tacheometric polar measuring technique. First of all, a distinction will be drawn between the terms traditional tacheometry, intelligent tacheometry, intelligent scanning, photo-tacheometry and laser scanning. • Traditional tacheometry Fundamental differences between intelligent tacheometry and traditional tacheometry (one could also say conventional tacheometry) have to be considered. Traditional tacheometry in this case stands for the use of the widespread reflectorless measurement method, utilizing a laser beam which is directed to the object manually. As far as hardware costs are concerned, intelligent tacheometry in comparison to conventional tacheometry adds a - rather negligible – 20%. The benefits outweigh the unique extra costs several times. • Intelligent scanning and intelligent tacheometry Intelligent scanning means scanning of predefined profiles, e.g. to determine the intersection between a plane with a building or, as it is done via laser scanning, to measure point arrays. To do this, there has to be feedback between the instrument and the object, which is provided by the controlling software. All tacheometric techniques focus on single points, whereas laser scanning initially delivers an unoriented point cloud, which is hardly adaptable to special circumstances. There is no feedback between object and measurement, i.e. no possibility to directly measure precisely defined profiles. The most important differences between intelligent scanning and laser scanning are point selectivity on site in intelligent tacheometry, and the high measuring speed in laser scanning. The costs for recording an object via intelligent tacheometry or laser scanning may also vary considerably. Intelligent scanning is part of intelligent tacheometry. Various surveying technologies, based on control circuit mechanisms, have been developed for the intelligent tacheometer: The ability to traverse feedbacks distinguishes the active, object-oriented intelligent totalstation fundamentally from the passive, not object-oriented laser scanner. Tacheometric methods are pointoriented; laser scanning is surface-oriented. • Photo-tacheometry