An Automatic Procedure For Mobile Laser Scanning Platform 6DOF Trajectory Adjustment

In this paper, a method is presented to improve the MLS platform’s trajectory for GNSS denied areas. The method comprises two major steps. The first step is based on a 2D image registration technique described in our previous publication. Internally, this registration technique first performs aerial to aerial image matching, this issues correspondences which enable to compute the 3D tie points by multiview triangulation. Similarly, it registers the rasterized Mobile Laser Scanning Point Cloud (MLSPC) patches with the multiple related aerial image patches. The later registration provides the correspondence between the aerial to aerial tie points and the MLSPC’s 3D points. In the second step, which is described in this paper, a procedure utilizes three kinds of observations to improve the MLS platform’s trajectory. The first type of observation is the set of 3D tie points computed automatically in the previous step (and are already available), the second type of observation is based on IMU readings and the third type of observation is soft-constraint over related pose parameters. In this situation, the 3D tie points are considered accurate and precise observations, since they provide both locally and globally strict constraints, whereas the IMU observations and soft-constraints only provide locally precise constraints. For 6DOF trajectory representation, first, the pose [R, t] parameters are converted to 6 B-spline functions over time. Then for the trajectory adjustment, the coefficients of B-splines are updated from the established observations. We tested our method on an MLS data set acquired at a test area in Rotterdam, and verified the trajectory improvement by evaluation with independently and manually measured GCPs. After the adjustment, the trajectory has achieved the accuracy of RMSE X = 9 cm, Y = 14 cm and Z = 14 cm. Analysing the error in the updated trajectory suggests that our procedure is effective at adjusting the 6DOF trajectory and to regenerate a reliable MLSPC product

Point cloud segmentation for urban scene classification

High density point clouds of urban scenes are used to identify object classes like buildings, vegetation, vehicles, ground, and water. Point cloud segmentation can support classification and further feature extraction provided that the segments are logical groups of points belonging to the same object class. A single segmentation method will typically not provide a satisfactory segmentation for a variety of classes. This paper explores the combination of various segmentation and post-processing methods to arrive at useful point cloud segmentations. A feature based on the normal vector and flatness of a point neighbourhood is used to group cluttered points in trees as well as points on surfaces in areas where the extraction of planes was not successful. Combined with segment merging and majority filtering large segments can be obtained allowing the derivation of accurate segment feature values. Results are presented and discussed for a 70 million point dataset over a part of Rotterdam