| Summary: | 碩士 === 國立成功大學 === 測量工程學系碩博士班 === 93 === Terrestrial laser scanner can rapidly acquire accurate and dense 3D point clouds covered on the surfaces of scanned objects such as buildings. The point clouds provide the detailed data necessary for accurate building modeling. In order to acquire complete data points on a scanned building, the scanning operations must be done at more stations. Each station has its own coordinate system representing the 3D position of each laser point. Therefore, all coordinate systems of different scanning stations must be transformed into a common system to register laser points acquired on different laser-scanning stations.
This thesis proposes a semi-automatic method for registration of terrestrial laser point sets acquired on 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 system. The transformation is bad in cases of inaccurate, or insufficient, or worse-distributed tie points. This paper suggests to apply 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.
|
|---|
