Creating and Editing Texture Coordinates (UVs) - An Introduction to Computer Graphics for Artists - page 161

Fig. 10.22 A texture layout for an architectural subject

the variety of options available for mapping a sphere. The techniques shown are a
fraction of the number of options available for any object.
The most important thing you need to keep in mind when you choose your
mapping layout is to understand what you want your map to look like in the end
(Fig. 10.22 ) . For this reason, it can be helpful to make sketches on paper of various
options you may think of before moving forward to projecting coordinates.

10.4.1 Mercator Projection

The default mapping layout for a sphere looks clean because of the small number of
seams, but it is heavily distorted (Fig. 10.23 ) . The method used is the Mercator
cylindrical projection . This type of projection is progressively more distorted as the
coordinates are farther from the equator of the sphere (Close 1908 ). Coordinates
in the upper and lower 30 % of the model are so distorted that they are nearly
unpaintable. This isn't a problem if the poles are meant to be uniformly white, but
if they need any other colors or defi nition, this solution is not satisfactory. For some
purposes, the UVs on this object are useless because of severe polar distortion and
moderate distortion everywhere else.