Practical Studies of Accuracy Enhancement Techniques for Terrestrial Mobile LiDAR Point Clouds in Engineering Surveys

Improving the accuracy of Terrestrial Mobile LiDAR (TML) data has been a challenge in Engineering Surveys. This research aims at how to innovatively enhance the accuracy of TML solutions through post-processing toward meeting high accuracy specifications in Engineering Surveys. Three techniques are described and implemented. Firstly, the linear feature-enhanced 3D Conformal Coordinate Transformation (3DCCT) is developed by employing ground control points (GCPs) together with linear feature constraints. Secondly, a two-stage Multistrip Adjustment (MA) technique is proposed that first co-register the overlapped TML strips using tie points and tie features extracted from them and then adjust the co-registered LiDAR data by applying the feature enhanced 3DCCT. Lastly, a post-processing technique for calibrating the LiDAR boresight errors of a terrestrial LiDAR system is tested out by using its own point clouds. Their usage has been strategically studied through their applications to field-test data. Specifically, multiple scenarios have been tested, analysed, and compared in terms of the usage of GCPs, the effect of feature constraints, MA and the effect of boresight error compensation etc. As shown from the results, their utilization is encouragingly contributing to the accuracy improvement of TML data towards the high accuracy demand for Engineering Surveys. A practical implementation dataflow is outlined at the end of this manuscript.