Automatic Registration of Point Clouds Acquired by a Sweeping Single-Pixel TCSPC Lidar System

Abstract: This project investigates an image registration process, involving a method known as K-4PCS. This registration process was applied to a set of 16 long range lidar scans, acquired at different positions by a single pixel TCSPC (Time Correlated Single-Photon Counting) lidar system. By merging these lidar scans, after having been transformed by proper scan alignments, one could obtain clear information regarding obscured surfaces. Using all available data, the investigated method was able to provide adequate alignments for all lidar scans.The data in each lidar scan was subsampled and a subsampling ratio of 50% proved to be sufficient in order to construct sparse, representative point clouds that, when subjected to the image registration process, result in adequate alignments. This was approximately equivalent to 9 million collected photon detections per scan position. Lower subsampling ratios failed to generate representative point clouds that could be used in the imageregistration process in order to obtain adequate alignments. Large errors followed, especially in the horisontal and elevation angles, of each alignment. The computation time for one scan pair matching at a subsampling ratio = 100%. was, on average, approximately 120 s, and 95s for a subsampling = 50%.To summarise, the investigated method can be used to register lidar scans acquired by a lidar system using TCSPC principles, and with proper equipment and code implementation, one could potentially acquire 3D images of a measurement area every second, however, at a delay depending on the efficiency of the lidar data processing.