The mathematics of perspective is given as follows (see Figure 6.12)
c: scale factor
(X0, Y0, Z0 ): center of projection or eye point
(X, Y, Z): terrain point to be converted
Firstly rotation around Z axis is given, then the rotation around X axis is given.
Bird's eye view in raster image is produced by combining DEM and the corresponding thematic data or satellite color image.
Hidden points are usually processed by the following two methods.
From far to close projection: from the order of further points along a profile all points are projected onto an image plane or perspective coordinate system. The nearest visible point will be output as the result. (see Figure 6.13 (a))
From close to far check: Z value of a ray is checked at small interval whether Z value is bigger than the terrain height or not. The first intersection will be output on the image plane. (see Figure 6.13 (b))
Examples of bird's eye view are shown in the front page of this book.