Self-calibration and direct georeferencing in terrestrial laser scanning

An important step in data processing from terrestrial laser scanning (TLS) is georeferencing, i.e. transformation of the scanner data (point clouds) into a real world coordinate system, which is important for their integration with other geospatial data. An efficient approach for this is direct georeferencing, whereby the position and orientation of the scanner can be determined in the field, similarly to the working routine of total stations. Thus the efficiency of the survey can be increased, and the project time and costs reduced. An important factor that affects the results of TLS surveys, especially those with direct georeferencing, is scanner calibration. In the recent years, the method of self-calibration used in photogrammetry has become popular for the recovery of systematic errors in laser scanners. This thesis has two main aims. The first one is to develop an approach for self-calibration of terrestrial laser scanners, which can be made available to users, and apply it to the calibration of a number of pulsed laser scanners in order to get a better insight into the systematic instrumental errors present in these instruments. The second aim is to investigate the possibilities for direct georeferencing in TLS in static applications, with the focus on the use of GPS for this purpose, and to develop a survey system based on the combination of TLS and GPS. An additional aim of the thesis is to make a systematic description of the error sources in TLS surveys, where direct georeferencing is employed. A good understanding of these error sources is necessary to secure the data accuracy. We subdivide these errors into four groups: instrumental, object-related, environmental and georeferencing. We have developed a unified approach for self-calibration of terrestrial laser scanners, where one can introduce stochastic information about all the estimated parameters, which helps in reducing their correlations. In part, it is possible to use direct georeferencing to det
QC 20100806
3D laser scanning of engineering constructions and historical monuments