Graphics Reference
In-Depth Information
Figure 14.17: Top: A video-game character from Team Fortress 2 rendered in real time
using Approximate Catmull Clark subdivision surfaces. Bottom: The edges of the subdi-
vision cage (projected onto the limit surface) in black, with special crease edges high-
lighted in bright green. (Credit: top: © Valve, all rights reserved, bottom: Courtesy of
Denis Kovacs; © 2010 ACM, Inc. Reprinted by permission.)
representation is particularly good for simulation, modeling, and measured data.
The control points may be irregularly spaced so as to efficiently discretize the
desired shape (e.g., a Triangulated Irregular Network (TIN), or the ROAM algo-
rithm [DWS
+
97]), or they can be placed regularly to simplify the algorithms that
operate on them. Because of their inability to model overhangs, heightfields are
often used as a modeling primitive and then converted to generic meshes. Those
meshes may be further edited without the heightfield constraint.
Heightfields, splines, implicit surfaces, and other representations based on control
points all define ways to interpolate data from a fixed set of points to define a
surface. As we increase the point density, the choice of interpolation scheme has
less impact on the shape because the interpolation distances shrink. A natural
approach to modeling complex arbitrary shapes is therefore to store dense point
