从中心投影影像制作正射影像的多种方法研究

Various methods for producing orthophoto out of perspective imagery

提出了由中心投影影像制作数字正射影像的三种新方法:(1)在具备立体像对的情况下,通过立体影像匹配求得视差值,直接利用视差值进行微分纠正,得到正射影像;(2)多中心影像不构成立体像对,但是各中心之间有一定的空间距离时,利用本文推导的一系列数学公式,可在影像匹配的基础上进行基于视差的微分纠正,从而得到正射影像;(3)直接利用地物稠密地区相应比例尺地形图的数字化成果,例如数字栅格地图(DRG)或数字线划地图(DLG),与单帧影像上提取的地物线划进行配准,从而实现正射影像纠正。还给出了影像上的特征线划与地图上的特征线划配准的新方法。

It is generally believed that the production of Digital Orthophoto Model(DOM) out of perspective imagery must adopt DEM(Digital Elevation Model) based digital differential rectification method with collinear equations as the mathematical model. According to this principle, DEM is indispensable besides a certain number of control points. This method has become very complete and popular through application, however, it is by no means the unique way. Three other non DEM methods in connection with various conditions of perspective imagery are proposed and discussed technically in this paper. (1) If the perspective sensed images are in the form of stereopair, then the parallax can be computed by stereo image matching and directly applied to differential rectification, bypassing the procedure of making DEM. (2) If the multi centered images do not meet the requirements of stereopair constitution, but definite spatial distances exist among the centers, then by using the mathematical formula derived in this paper, parallax based differential rectification on the basis of image matching can be done. Figures and formula illustrate that such ill geometrical condition does not seriously affect the results quality. (3) If the topographic data, such as DRG (Digital Raster Graphics) or DLG (Digital Line Graphics), of the area distributed with dense objects, are available, then orthophoto rectification can be implemented by registering the feature lines out of DRG or DLG with those extracted out of a single image. This method gives rather satisfactory result in the area of smooth relief. Besides, a new method based on mathematical morphology used for the matching of feature lines is also given.