Creating and Editing Texture Coordinates (UVs) - An Introduction to Computer Graphics for Artists - page 172

would have zero map area. If the map is much larger, the UVs would have to be
much smaller to have zero map area. Because of this, it is useful to set the resolution
of your maps based on the smallest map and then work up to larger ones, rather than
the other way around.
If you have zero map area polygons, you should either increase their size within
UV space, or attach them to a different material that uses a smaller texture map.

10.6 Packing

10.6.1 Introduction

“Packing” describes the process of arranging UVs so that they fi ll the available texture
space as densely as possible. A well-packed UV set will reduce the number of unused
pixels in a map. Some objects will use almost all of the available space because they
are made entirely of right angles, but other objects are the wrong aspect ratio, or have
to be combined with other parts on the same map, or are not built of right angles. Most
objects can be packed into about 80 % of the texture space without distortion.

10.6.2 Overspray

When a pixel intended for one polygon strikes it and another because the UVs are
too close, it is called overspray (Fig. 10.37 ) . To prevent overspray, a one to three
pixel wide margin should surround each discrete group of UVs. Otherwise, it is
possible that a pixel meant for one polygon will bleed into another because the UV
borders are less than a pixel apart. The reason there is a range instead of an absolute
value is because it depends on the resolution of your texture map. The lower the
resolution, the farther apart the pieces must be because each pixel covers a propor-
tionately larger area of your UV space.

10.6.3 Texture Orientation

It is possible to project UVs so that they are oriented as you like, but sometimes they
must be edited after the fact. It is generally best if all parts are oriented with their
topmost points at the top, bottom points at the bottom, and so on. The reason is that
it is usually easier for a texture artist to paint things that are oriented right side up
than to paint them at an angle, backward (Figs. 10.38 and 10.39 ) or upside-down.
Sometimes, you may want to rotate the UVs at an odd angle, to make the best use of
texture space (Fig. 10.38 ). If you do this, the texture artist may have to paint the
object with a 3D paint tool, or will have to exercise greater care when painting in 2D.