Shaders and Texturing - An Introduction to Computer Graphics for Artists - page 206

Fig. 11.30 A tiling map like the two in this fi gure can be repeated indefi nitely without breaking
the pattern

11.5.6 Terrain Maps

Large objects such as terrain are diffi cult to texture with a single map because the
surface area is too large to cover without visible pixelization. Pixelization is when
individual pixels are clearly visible in the map, sometimes to such a degree that the
image on the map is unclear. Tiling, tile sets and blend maps are used to cover large
areas with small texture maps without sacrifi cing resolution.

11.5.6.1 Tiling

Tiling allows a small map to cover a large area by repeating the image many
times within its texture boundaries (Fig. 11.30 ). Its major drawback is that the
tiling pattern is usually easy to spot and tends to make objects less convincing to
a viewer. This can be mitigated if the tiling effect is carefully hidden by careful
control of the map's major features, but even this usually isn't enough to disguise
the tiling. Tiled textures may also create disturbing Moiré patterns on your
screen. This is when a regular pattern, your map, is viewed through another regu-
lar pattern, your monitors' pixel grid, and an interference pattern is created
where they cross. If you do not want a Moiré pattern, you will have to use a dif-
ferent solution.

11.5.6.2 Tile Sets

Tile sets allow a group of small maps to be applied to sections of a model that are
divided by edges used as texture boundaries. Tile sets have a much larger number of
UVs than would be present on a similar model where tile sets are not used. This is