Corner features for unifying coordinate systems of multiple liDAR stations

This paper proposes a semi-automatic method for registration of terrestrial laser point sets acquired at different stations. Firstly, a point cloud on a local plane is selected manually, and then a mathematical plane is fitted in a least squares manner onto them. Three local planes on an object corner are thus respectively determined, and their intersection point is computed by solving these three plane equations. Such points are used as tie points for transforming different laser coordinate systems into a common one. The transformation is bad in cases of inaccurate, or insufficient, or worse-distributed tie points. This paper adopts suitable "virtual corner points" to solve this problem. The test results show that suitable virtual corner points really can improve the geometrical condition for the transformation and thus raise the accuracy of corresponding transform parameters with the improvement rate of 36% to 71%. On the other hand, the ratio of the RMSD-value to the scanning distance S becomes a constant of 0.00015 in case of S ≫ 50m, where RMSD denotes the root mean square value of the perpendicular distance from a laser point to its corresponding plane.