An ortho-image production method from stereoscopic images
Nobuhiko Mori
Osaka Institute of technology
1-79-1, Kitayama, Hirakatashi, Osaka, 573-01, Japan
Tel : (81)-720-66-5390 Fax : (81)-720-66-8380
Email :nmori@ij.oit.ac.jp
Abstract
An ortho-image is usually made using both an image and a DEM (Digital Elevation Model) of the same area. In this paper, a new method is proposed, which produce an ortho-image from streoscopic images directly. Because two images of the same are used in this method, some image corrections, such as partial replacements and arithmetical calculations on images, can be carried out to make a fine output of an ortho-image. This method can be realized by modifying the software of a digital photogrammetric system slightly.
1. Introduction
It is well known that ortho-images are necessary to make stereoscopic images of any B/H ratio, or bird's eye view images from any view point. But nowadays they are more frequently used in GIS (Geographic Information System), because they can be overlaid directly on many kinds of maps in the system. Ortho-images are usually made using DEMs and images with orientation elements. Because there are few kinds of available DEMs now, those DEMs are very often extracted with appropriate interval from topographic maps with contour lines or stereoscopic images. There are many proposed methods to extract DEMs from contour lines automatically by computer. When stereoscopic images are used, DEMs are extracted by using digital photogrammetric system. It is a very cumbersome work to make an ortho-image, because there are two steps in the work, a DEM extraction and an ortho-image production.
2. An example of an ortho-image production method using a DEM
An ortho-image is usually made from an image with orientation elements using a DEM. Figure 1 shows a common procedure to make an ortho-image using a DEM. In this case, a satellite image, such as SPOT or JERS, is changes into an ortho-image. In this figure, a DEM is extracted from contour lines of topographic maps. Orientation elements of the satellite images are determined using GCP (Ground Control Point) positions on both the satellite image and topographic maps. Data of orbit and attitude of the satellite is used in the extraction of the orientation elements are determined as the functions of time. The output ortho-image is made using the input satellite image, the orientation elements and the DEM. Photo 2 is an example of the output made by this method. The input image is a SPOT image of Hishikari District in Japan.
Figure 1 A method for making an ortho-image using a DEM
Photo 2 An ortho-image of the Hishikari district in Japan
