Creating and Editing Texture Coordinates (UVs) - An Introduction to Computer Graphics for Artists - page 159

Fig. 10.19 By shifting the UVs, their shape no longer matches the polygons they are mapped to
and distortion occurs

moderate, the object will have to be painted in a 3D paint program instead of as a
2D map. This will take longer to execute, but will allow the artist to ignore the dis-
tortion. Serious distortion may be unpaintable.
In Fig. 10.19 , the UVs have been modifi ed so that they no longer match the shape
of the polygons they are mapped to. Most artists would never do this on purpose, but
it can happen accidentally. Notice the distortion shear along the implicit triangle
edge (Fig. 10.20 ) .
Just as distorting the position of UVs causes distortion, changing the position of
vertices relative to each other does the same thing (Fig. 10.21 ) . This is common in
character models because polygons in joint regions distort during movement. Now
the UVs still have the same shape and aspect ratio, but the polys do not. Whenever
this is true, textures will be distorted.
Figure 10.21 is the same object pictured in Fig. 10.20 after having a new planar
projection applied to face B. Now the mapping is undistorted on that face. As you
can see, the shape of face B matches its corresponding UV layout exactly. This is
necessary for undistorted mapping.

10.4 Choices

There are many UV mapping solutions that will work for any given object, and none
of them is necessarily “perfect”. Some methods may seem obviously wrong and yet
they work for a specifi c purpose and vice versa. This section provides a sampling of