Study on promoting the accuracy and the efficiency of scanning buildings by 3D laser scanner using conjugated 3D sphere markers

本研究以雷射掃描儀作為掃描建築物之工具，採用三維球型覘標作為相鄰測站間之共軛覘標，探討雷射掃描儀對於不同尺寸之共軛覘標在不同掃描距離條件下之球心坐標精度；及利用檢校場之固定樁位，求得雷射掃描儀與各覘標之距離誤差量，並建立距離誤差量改正模式；最後，提出最佳之掃描方式。 本研究分別選定三個場地作為不同實驗區，先選定一處室內場，以三種尺寸之三維共軛球型覘標，規劃距離儀器原點5公尺至40公尺，以每5公尺之等距離方式分布，並依序掃描，以求得球心坐標精度；再選定台中國土測繪中心之距離標準基線場，以雷射掃描儀直接掃描三段距離，分別為5公尺、23公尺及31公尺，以求得掃描儀之距離誤差；最後選定一建物，以一般掃描及較佳掃描之方式各別進行建築物掃描，以分析兩者間之效益。 依成果顯示，於相同掃描距離下，三維共軛球型覘標尺寸越小，其球心坐標精度越差；相同三維共軛球型覘標之尺寸，其球心坐標精度將隨著掃描距離增加而越差。另外，透過距離檢校場，可得知該儀器之系統性誤差，並建立其距離誤差改正模式，用以改正所獲取之點雲之系統性誤差，以提升三維點雲模型之精度。 最後將較佳掃描之方式與一般掃描情況下，進行實際掃描並比較分析兩者之數據，依成果顯示，於一般掃描作業及較佳掃描作業情況下，直徑14.5公分之三維共軛球型覘標較直徑12公分之三維共軛球型覘標，皆節省25％之掃描時間。而兩者之點雲模型精度相仿，且皆符合建築掃描精度要求於1 cm內之精度，可以得知最佳掃描效益能夠縮短掃描作業時間，並提升點雲模型之精度。This research uses laser scanner as the scanning tool, and 3D sphere marker as the conjugated marker between neighborhood stations, to investigate the accuracy of sphere center coordinates of different-sized 3D sphere markers at different scanning distances; calculate the distance errors between laser scanner and every marker with the fixed survey stations in the calibration field and establish distance error correction formula. At last, propose the best way to scan buildings according to the experiment results. Three different fields are selected as experiment areas. First, choose an indoor field, and scan three different-sized conjugated 3D sphere markers. Every conjugated marker is scanned at distances of 5 to 40 m at an interval of 5 m. Second, choose the standard baseline field of National Land Surveying and Mapping Center in Taichung as the experiment area, and use laser scanner to measure the distances of 5, 23 and 31 m to calculate scanning distance errors. At last, choose a building as scanning target, scan it in general way and efficient way respectively, and analyze the differences between the two methods. According to experiment results, the smaller the conjugated 3D sphere marker is, the worse the accuracy of sphere center coordinate will be at the same scanning distance; as the scanning distance gets longer, the accuracy of sphere center coordinate will decrease with the same size conjugated 3D sphere marker. On the other hand, the systematic error of the instrument can be known through the distance calibration field. With a known systematic error, a distance correction formula is established to correct the systematic error of the point cloud, and hence improve the accuracy of 3D point cloud model. Eventually, compare and analyze the differences of the results getting by the most efficient way and the general way of scanning. The results show that both scanning methods save 25% scanning time using 14.5-cm-diameter conjugated 3D sphere marker compare to using 12-cm-diameter conjugated 3D sphere marker. And the data represent that the point cloud models in the two situations have similar accuracy, and the accuracy of each model is better than 1 cm, which means they both meet the precision requirement of building scanning. Consequently, the most efficient way of scanning mentioned in this research can shorten the time of scanning work and improve the accuracy of point cloud model