Quantitative Evaluation of Scaling Factor on Coordinate Transformation for Time-of-Flight Terrestrial Laser Scanner

Terrestrial laser scanning is a new approach in three-dimensional measurement. Since the acquisition of terrestrial laser scanner data requires multiple scanning stations to complete the data of a scanned object, the coordinate transformation process is the inevitable procedure in the measurement phase of the laser scanner. However, neglected scale factors in the process of terrestrial laser scanning datum transformation have led to a dispute over the quality of the laser scanning data. Emerging of errors not only occurs during data collection phase but it also occurs during data processing phase involving the use of algorithms. For a comprehensive assessment of these scale factors, two experiments have already been conducted involving multiple-networks experiment and multi-distance experiment. Multiple network experiment is performed with the establishment of multiple scanning stations (from 2 to 7 stations) and some real object surfaces equipped with artificial targets. The multi-distance experiment involves various scanning distances provided by the time-of-flight terrestrial laser scanning, involving testing from 60m to 140m. The registration process is then performed to produce all 7 parameters including the scale factor calculated between the scanner positions. The statistical method, with hypothesis testing, is used to evaluate the scale factor that is calculated with the ideal value. The results show that in all configurations, the null hypothesis is accepted with a 95% confidence level. This result also stipulates that scale factor can be ignored in datum transformation process for terrestrial laser scanning.