Lidar Strip Adjustment Using Automatically Reconstructed Roof Shapes

LiDAR systems have been established as technology for fast and high-resolution acquisition of 3D point clouds. In general, LiDAR data acquisition is conducted by private companies who are also responsible for processing and quality control. However, in many cases a subsequent quality assessment of overlapping LiDAR strips still reveals apparent horizontal and vertical offsets which are caused by undetected systematic errors (e.g. insufficient calibration and strip adjustment). The presented work covers methods for the detection of remaining discrepancies in overlapping LiDAR strips with main focus on the development of a new precise 3D measurement technique based on intersecting roof ridge lines and roof planes which are automatically reconstructed from the LiDAR point clouds in overlapping strips. The coordinate differences between conjugate intersection points are incorporated in an adjustment process to resolve for the residual errors of each LiDAR strip separately. The new 3D reconstruction method can also take advantage of full waveform measurements like pulse width and intensity which are decomposed from the waveforms. Finally, the LiDAR strips are corrected and validated by checking the correspondence among neighbouring strips. The quality control system has been successfully applied to pre-processed and adjusted LiDAR strips. In general, the results show that significant discrepancies mainly in position still exist. After the adjustment of 8 strips (altitude 1000 m) using precise 3D measurements, the relative horizontal displacements between adjacent strips are improved by more than 70 %. * Corresponding author.