地形圖掃瞄與數化位置精度之研究

Abstract

摘要 目前國土資訊系統（National Geographic Information Systems ；NGIS) 之九大資料庫中，以基本地形圖資料庫最具基礎性及應用性。而 數值地形圖的建置與供應為實施國土資訊系統的首要工作，幾乎所有後續 的應用均需以數值地形圖的內容為底圖，進行地理資訊分析。數位資料的 正確性及品質好壞，直接影響後續作業分析成果之可用性及可靠性，錯誤 之資料可能影響決策的品質，甚至導致錯誤的決策。因此，對數化的資料 實有必要進行評估。 本論文主要探討地形圖掃瞄與數化之精度。針對研 究區域之數值地形圖，以隨機取樣的方式，選取明顯地物點，如兩道路線 之交叉點，當成檢核點；以細線化的方法將掃瞄的原始影像細化處理，反 推其掃瞄影像圖上相對應的像點，比較數值成圖之物點座標與掃瞄稿圖之 像點座標，而探究數化製圖過程所產生之誤差。 實驗結果發現：（1） 道路圖層有74.28%位置誤差小於圖上0.5mm、水系圖層有53.13%位置誤差 小於圖上0.5mm，僅合乎二級精度之要求。誤差主要來源為數化過程產生 之誤差及其座標轉換誤差傳播之結果。（2）數值資料之良窳關係地理資 料分析結果之精確，須有完整精度檢核之程序，方能了解數值資料之誤差 分佈情形。關鍵字：數值地形圖、精度檢核、檢核點

Abstract Digital topographic maps are the most fundamental among the nine databases in the National Geographic Information System (NGIS). Theestablishment and supply of the digital topographic maps are primary work of the implementation of NGIS. Digital topographic maps are used in many applications as base maps to proceed various kinds of geographic analyses. Thequality and accuracy of the digital data affect the usability and reliability of theresult of the geographic analysis immediately. Using wrong data in the process of decision making would degrade the quality of the decision made, or even cause the wrong decisions. Therefore we should evaluate the quality of the digital data. The purpose of this research is to explore the positional accuracy of the scanned and digitized topographic maps. Based on the digital topographic mapsof the study area, obvious local image points such as intersections of road lines were chosen as check points. Line thinning algorithm was applied to thin thescanned image for obtaining corresponding points on the scanned imageCoordinates of these points from digitizing and scanning were compared toexplore the errors due to digital scanning process. Two findings are drawn from the experimental results of this research. (1) Positional errors of 74.28% of check points of the road layer and 53.18% of the water layer are less than 0.5mm on map which comfort to the second graderequest. The primary sources of errors are from the results of the map digitizationand coordinate transformation. (2) The quality of the digital data affects theaccuracy of the result of GIS''s analyses. Complete procedures of accuracyassessment must be established to understand the distribution of errors from data collection to applications. Keyword : Digitized topographic maps, Accuracy assessment, Verifiedpoint