截距法繪製船位之截距誤差與方位角誤差及其對船位之影響

The Effect of Intercept Errors and Azimuth Errors of the Intercept Method for Determining Ship's Positions

以傳統截距法繪製船舶位置線以決定船位時，易因位置線及方位角之繪製誤差而影響船位。本研究先請航行員以假設船位、真方位及截距繪製船位位置線取得繪圖樣本，進而將繪圖樣本掃瞄為影像檔，再以視窗程式讀取影像檔並加以計算，以與真實截距長度及方位角相比對，求取繪圖截距長度及方位角誤差。最後分析繪圖誤差之分佈現象與繪圖誤差對船位之影響，應用截距法向量解析法配合電腦程式計算船位，計算出船位誤差範圍，以提供航行員於繪製船舶位置時參考。研究結果顯示：（1）截距誤差與方位角誤差均呈現高斯誤差密度分佈。（2）截距與方位角誤差在一標準差之情況，位置三角形單點變化介於0.8浬至11.8浬之間：平均船位之變化量介於1.7浬至6.9浬。（3）截距法向量解析法配合電腦程式能快速且正確計算出船位，與傳統繪製之結果相差微小。 To determine the plotting ship position by the traditional intercept method, the ship's positions are likely to he deviated from attended ship's position due to the azimuth and intercept plotting errors. In this research, samples of experiment were plotted on the Mercator plotting chart b the navigators Then, the plotting samples were scanned and calculated by use of special designed computer program so that the results could be compared with the assigned line of position (LOP). Based on the comparison, the range of possible errors was obtained through the use of vector solutions of intercept method via computer computation. The results of the research show that: (1) The errors of intercept and azimuth probability density corresponded to Gaussian error distribution curve. (2) Under the circumstance of one standard deviation of the errors of intercept and azimuth, the single point position deviation of the ship position triangle formed by the intersection of the three lines of position varied from 0.8 to 11.8 nautical miles; while the mean ship's position varied from 1.7 to 6.9 nautical miles. (3) The ship's position can be obtained fast and accurately by use of the vector solutions of intercept method via computer computation with minor differences from the result of plotting.