| 摘要 |
PURPOSE:To omit maximumly calculations for an invisible earth's surface to generate an airscape image in a high speed by setting calculation parts, which are not dependent upon topography, as constant data preliminarily and calculation parts, which are dependent upon topography but are not dependent upon relative relations to a visual point, preliminarily for each visual point and calculating the airscape image successively from a position near the visual point. CONSTITUTION:Information which are not dependent upon the visual point of the airscape image but are dependent upon only topography of the earth's surface are calculated preliminarily and are stored in a topography alititude information file 12. Many triangles of the earth's surface correspond to one picture element on the airscape image with respect to the earth's surface at a point distant from the point just under the visual point of the sirscape image though topography of the earth's surface is approximated to triangles, and an unnecessary calculation time occurs in the resampling processing. Consequently, it is proper from the viewpoint of uniformity of the resampling precision on the airscape image that topography of the earth's surface near the visual point is approximated to small triangles in details and that distant from the visual point is approximated to large triangles. Next, the airscape image is obtained from plural visual points for one topography of the earth's surface.
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