Generation of Digital Orthoimages from High Resolution Satellite Images

要旨

Digital orthoimages are the fundamental products for image maps, GIS image base, cartographic extraction, and map revision. This study investigates the methodologies to generate 1:5000/1:10 000 orthoimages. Based on the required accuracy standards we have developed an error budget model for the horizontal position and vertical position of a ground control points (GCP) and digital elevation model (DEM). The model then determines the methods to collect GCPs and the accuracy of a DEM. Two tests were conducted in Hong Kong to produce orthoimages with IKONOS Geo products at scale of 1:5 000 for various terrain conditions. One is in a hilly area covering the both sides of the Victoria Harbor with elevation ranging from 0 to 400 m, and the other is in a mountainous area covering Tai Mo Shan with elevation ranging from 0 to 950m. Different software and number of GCPs were used in the tests. The results indicate that it is possible to produce orthoimage at scale of 1:5000 for various terrain conditions with IKONOS Geo images and 7-11 GCPs per image provided careful design and operation of a project are exercised. Another test was also conducted to produce 1: 10 000 orthoimages with SPOT 5 images of 2.5m resolution. The test area covers the whole Hong Kong.