由於IKONOS衛星影像具有甚高之空間解析度，對於大比例尺製圖而言具有相當高的潛力。因此本研究之重點即為考慮地形起伏、建築物存在及相互遮蔽問題之IKONOS衛星影像正射化為主要工作。 就IKONOS衛星而言，無法取得原始影像，因此以其使用率最高的GEO等級影像為本研究之標的。因考慮地形及房屋在影像中所造成的遮蔽，故所產生之正射影像稱為“真實正射影像”。 研究之方法包括：(1)對地面控制點進行高差移位改正，(2)進行影像坐標與地面坐標間之二維轉換，(3)對正射影像之每一個像元進行反投影，(4)使用數值地形模型進行前步驟所得像元之高差移位校正，(5)影像重新取樣。針對真實正射影像之產生尚需進行房屋區高差移位校正及遮蔽區處理。實驗成果顯示，在僅使用6個地面控制點之情況下，不論是僅考慮數值地形模型所產生之正射影像或使用房屋模型所產生之真實正射影像，其定位誤差均優於2m。 Due to its high spatial resolution, IKONOS imagery has a very high potential for large-scale topographic mapping. The focus of this investigation is performing the geometric correction for the IKONOS satellite images. Since raw image data would, in general, not be provided by the satellite company, we have developed a method that performs the rectification of IKONOS GEO images. We also considered the occlusions caused by terrain and buildings, thus, the generated orthoimages will be called the True “Orthoimage”. The proposed scheme includes the following steps: (1) the correction of relief displacement for GCPs, (2) the performing of two dimensional transformation between the ground coordinate system and the image coordinate system, (3) the performing of back projection for each pixel in the orthoimage, (4) the use of DTM to calculate the relief displacement for the pixel in the previous step, and (5) image resampling. Relief corrections for buildings and occlusion process will also be handled toward generation of true orthoimage. The experimental results indicate that the generated orthoimages, including the ones by using DTM and the one considering building effects, may reach an accuracy of 2 m, when 6 GCPs were employed.
