萃取物表角面特徵點供多測站地面光達點雲面之連結

Extracting Corner Points for Registration of Terrestrial Multi-Station LIDAR Scanned Surfaces

蔡展榮(Jaan-Rong Tsay) ； 李姝儀(Shu-Yi Lee)

《航測及遙測學刊》 11卷4期 (2006/12) Pp. 339-359

https://doi.org/10.6574/JPRS.2006.11(4).1

摘要

本文提出一個半自動化的多測站地面光達點雲面連結方法，它是從雷射點雲萃取被掃瞄物表面上的局部角面特徵點並求定其三維坐標，進而將這些共軛角面特徵點做為連結點，把多個光達測站點雲轉換到同一個物空間坐標系統中，俾行資料連結整合之用。而在實務上，會有角面特徵點品質不佳、點數少、或分佈不佳的情況，所以本文以加入適當的「虛擬角點」的構想來解決此一問題；本文實驗成果顯示，在前述的情況下，加入適當的虛擬角點可改善連結點的幾何分佈強度，使得整體坐標轉換參數精度可提升36%~71%。掃瞄距離S大於50m時，局部平面點雲到最小二乘擬合平面的距離均方根值RMSD和S之比值RMSD/S約收斂於常數0.00015。

關鍵字

光達 ； 最小二乘擬合 ； 角面特徵點 ； 連結點 ； 坐標系統

並列摘要

Terrestrial laser scanner can rapidly acquire accurate and dense 3D point clouds covering 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 laser scanning stations must be transformed into a common system to register laser points acquired on different LIDAR stations.
This paper 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 one. 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 strengthen the geometrical configuration for the transformation and thus raise the accuracy of corresponding transformation 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, where RMSD denotes the root mean square value of the perpendicular distance from a laser point to its corresponding plane.

並列關鍵字

LIDAR ； least squares fitting ； corner feature point ； tie point ； coordinate system