地面雷射掃瞄儀可在短時間內獲取大量的高精度點雲資料，可視為密集覆蓋在物體表面上的量測點，能提供物體豐富的細節資訊，廣泛應用於各領域之三維模型重建工作。然而，雷射掃瞄儀受掃瞄範圍之限制，導致單一掃瞄站之掃瞄區無法完全涵蓋被測物，因此需以多測站施測之，再將這些測站坐標系轉換至同一個坐標系統，俾以連結多測站光達點雲資料。
　
　　本研究即提出一個半自動化的地面LIDAR多測站點雲連結方法，從雷射點雲萃取被掃描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群做為連結點，把多個LIDAR測站點雲轉換到同一個物空間坐標系統中，作為資料連結整合之用。然而實務上，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分佈的幾何強度，使得相關的測站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。

　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.

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http://nhmrc.cv.nctu.edu.tw/People/tyshih/Publications/35.pdf

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