車載光達移動測繪系統率定作業及精度分析

The ealibration and precision analysis of LiDAR Mapping System (LMS)

車載移動測繪系統結合精密整合式定位定向系統、光達、數位影像感測器等，具有高機動特性，可補足航遙測資料獲取的空隙，加速空間資料獲取。內政部國土測繪中心於106及107年度完成光達移動測繪系統（LiDAR Mapping System, LMS）建置，期能掌握先進測量技術並發揮其測繪能量，以達到圖資快速更新，提供國家經建政策規劃推動及防救災領域所需及時且正確的基礎圖資。為持續精進移動測繪系統成果品質，108年度針對現有測繪車光達及影像感測設備辦理相關率定作業之需求，進行資料蒐集，盤點國內車載移動測繪系統的種類與數量，以及近年來國內、外與車載移動測繪系統率定技術相關之應用文獻，評估未來辦理車載移動測繪系統率定場規劃作業，參考文獻既有技術研擬率定標準作業程序，俾利後續建置移動測繪系統率定場。本研究研提LMS率定程序，感測器包含定位定向系統、光達，率定項目包含軸角及固定臂，參考率定技術介紹及率定場選擇原則，建議率定場透空度可達50度以上，適合GNSS接收且可減少GNSS訊號受到遮蔽或多路徑效應影響；光達式率定場需進行往返軌跡掃描，使用點或面之型式進行率定解算，建議現地包含一棟建物及前方有空地情況，軌跡路線包含左右、前後往返掃描資料，以及與建物45度角運行方向進行點雲資料蒐集，以利蒐集往返及不同方向交會點雲資料。針對車載移動測繪系統率定程序，光達式LMS系統建議選用TerraMatch之軸角及固定臂率定作業流程，辦理國土測繪中心及RIEGL車載移動測繪系統率定試辦作業，試辦作業於成功大學歸仁校區之室外率定場進行。試辦成果顯示，本研究研擬之率定方法，可成功求得軸角率定成果，將率定成果帶回點雲進行修正，測繪中心及RIEGL光達式LMS其直接地理定位點雲平面精度為0.141公尺及0.044公尺、三維精度為0.204及0.073公尺，相關成果可應用於國土利用調查及臺灣通用電子地圖圖資更新等作業。

LiDAR Mapping System (LMS) integrates precise integrated positioning and orientation system, LiDAR, with high flexibility, which can fill the gap in aerial data acquisition and speed up the spatial data acquisition process. National Land Surveying and Mapping Center (NLSC) completed the construction of LiDAR Mapping System (LMS) in 106 and 107, hoping to update the map rapidly and provide timely and correct basic map for the promotion of national economic construction policy planning and the field of disaster prevention. In order to improve the quality of the results of the LMS, this research focuses on the issue of LMS calibration. The information about each kinds of mobile mapping system in our country has been reviewed, and the references that discussing about the calibration methods are also be collected. A calibration procedure for LMS is proposed in this research. The sensors contain positioning and orientation system and LiDAR. This research focuses on the issue of boresight and lever arm calibration. According to the principle of calibration field selection, the transmittance of the calibration field should be more than 50 degrees, which is suitable for GNSS reception and can reduce the effect of GNSS signal blocking and multipath effect. A good calibration field is an open space with hard surface ground and without disturbing objects such as cars or trees. At least on one large building without many detailed structures is recommended in the field. The calibration route includes two drive paths in opposite direction parallel to the vertical surface, two drive paths in opposite direction perpendicular to the vertical surface, and two diagonal drive paths towards or away from the vertical surface. TerraMatch program is suggested for the boresight and lever arm calibration procedure. NLSC LiDAR Mapping System and RIEGL LiDAR Mapping System are calibrated in the pilot region, the outdoor calibration field located in NCKU Kuei-Jen campus in Tainan. LMS with proposed calibration procedure can get the boresight angle and lever arm results successfully. The preliminary results about point clouds of positioning accuracy in direct georeferencing mode show that the 2D precisions of NLSC and RIEGL LiDAR Mapping System are 0.141 and 0.044 meters respectly, and 3D precisions are 0.204 and 0.073 meters. The relevant results can be applied to land use surveys and map updates of Taiwan Electronic Map.