CG Modeling 2: NURBS - An Introduction to Computer Graphics for Artists - page 268

Fig. 14.31 By using curves as the basis for polygonal objects, you ensure that vertex distribution
along the curve is perfect for length and amount of curvature. As shown above , reducing curves to
polygons involves area loss. This is minimized when working from curves
If you intend to make a polygonal object out of your NURBS model, you should
keep the following in mind:
• Subdivision type: non-uniform NURBS objects will usually place vertices based
on your objects' curve weighting. The result may not be what you expect. It is
possible that the product will have a high number of small polygons in a dense
cluster near CVs with a high weight value relative to their neighbors. To elimi-
nate this, you can ask your program to divide your surface based on its isoparms.
If you do, you will see that a great deal of your curve detail is cut away. This is
because the curves occur between isoparms. To retain this curvature, you will
have to subdivide the surface between isoparms one or more times, or add
isoparms between them, to catch this curvature.
• A NURBS object can be subdivided uniformly, but if you do, know that the poly
count of your polyset will be very high and you may cut out curve detail that you
would rather retain.
• Keep an eye on areas of greatest curvature. These are the parts of your model that
benefi t the most from the NURBS primitive geometry type, but also the areas
that tend to generate the largest number of polygons in the conversion process.
Once you have experimented with this a few times, you will have a better idea
how to prepare your model for conversion.
• If your model has any coincident CVs, as it will on a sphere, then you will want
to weld these after they have been converted to vertices in a polygonal model.
Failure to do so will unnecessarily increase the complexity of your model and
affect how it is texture mapped.