Creating and Editing Texture Coordinates (UVs) - An Introduction to Computer Graphics for Artists - page 170

Fig. 10.34 The default UVs on a NURBS cylinder are the same as for a circle extruded into the
shape of a knot. In both cases, no editing is necessary

There are a number of object types, like wires, knots, arches, clothing, and string
that are most easily mapped by using default coordinates prior to molding the object
into its fi nal shape. A rope can be built straight, and then knotted after the fact, thus
retaining the original UVs (Fig. 10.34 ). It is important to be on the lookout for this
type of object because it can be very time-consuming to add new UVs to objects like
this after they have been molded into their fi nal state.
The best-case scenario is to always have an idea how your object should be
mapped before you build it. Mapping and texturing can take much more time than
modeling, but much less if the UVs are planned for.

10.5.3 Defi ning Seams

The number of seams is important, but so is the location of seams. Imagine the label
on a jar cut in half by a texture seam. If this happens, the artist must build the map
as two separate sections that line up perfectly in the middle. If it is possible, and it
usually is, it would be better to use a layout that allows the entire label to be made
as one contiguous texture. Almost all objects can have their seams in many different
locations without changing the UV projections. When you decide where the seams
should be, it is important to consider the type of map that will be used and where it
will go. For example, the cap of a cylinder can be pie-cut to the center or a boundary
placed around its perimeter (Fig. 10.35 ). Both will have the same number of edge
seams, but the perimeter describes a logical boundary and allows more contiguous
faces to be painted together (those around the column and those on top).

10.5.4 Zero Map Area UVs

If the polygon defi ned by a group of UVs covers less than a pixel of space on a
texture map, it has zero map area (Fig. 10.36 ). This means that the polygon will
take the color of whatever single pixel it resides within, and no other. If a polygon
has zero map area, there is no point to using a map, because the diffuse color of
the material it is connected to can accomplish the same job with less effort and the
savings of several unnecessary UVs.