Optimization of CG Models - An Introduction to Computer Graphics for Artists - page 108

Fig. 8.8 Polygons that don't contribute to its silhouette can often be replaced with texture maps
(Model courtesy of Tobias Koepp)

8.14 Fake Perspective

For models that are meant to represent large areas of terrain, if the camera will never
stray outside clearly defi ned boundaries, terrain that lies beyond those boundaries
may be artifi cially shortened to reduce overall poly count. To be effective, a consis-
tent scale must be used, where concentric contour rings (whether they are ring
shaped or not) describe a certain distance from the camera, and objects between
each successively distant pair of rings are scaled down and brought closer. This
means, for instance, that if all objects are built at 1:1 scale within the nearest camera
range, the next group out would be 75 % their original size, the next group beyond
that would be 50 %, then 25 %, and so on. This method is most effective if used in
combination with environmental fog, non-fl at terrain, and an irregular (not square)
terrain border (Fig. 8.9 ).

8.15 Card Geometry

This is the most extreme form of optimization. Card geometry is a completely fl at
four-sided polygon with a texture map to defi ne all its details instead of geometry.
For this to work, there is a color map, sometimes based on a render of a more com-
plex object, an opacity map to defi ne the object's silhouette, and sometimes a bump
or normal map to enhance the model's depth. Card geometry is used to represent
complex objects such as plants or distant buildings or landscape elements (Fig. 8.10 ).
An enhancement to the technique is to use multiple intersecting cards to cause real-
istic overlap of elements.