I’d like to see if we can get some closure on this subject. It’s been quite a controversy, and regardless of it’s actual impact on modeling, I’d like us to finally resolve the issue.
LW, MAYA, C4D, XSI, Mirai, Nendo, and Max et all have some form of Sub-d modeling. But it has come to many people’s attention that they differ wildly in their implementation. Phrases like “yeah, but max doesn’t support TRUE catmull-clark surfaces” abound.
Since I see these phrases so frequently, I can no longer differentiate between what is true, and what is myth. Some of you may know that myself and a group of CGTalkers are creating an all encompassing Sub-D FAQ that lists and explains methods,
terminology, and theory. For my research and documentation to continue, I would really like to get your take on the matter.
This is a bit dry, I know, but what good is a huge CG forum if we can’t talk about esoteric modeling methodologies?
Let me start with a quote:
"What we know today as “Sub-D” was originally described in “Recursively generated B-spline surfaces on arbitrary topological surfaces” by E. Catmull and J. Clark (Computer-Aided Design 10(6):350-355, November 1978).
The algorithm was written by Ed Catmull, a co-founder of Pixar Animation Studios.
When a polyhedron is subdivided with the Catmull-Clark method, new vertices (called “face points”) are placed at the center of each original face, new “edge points” are similarly placed at the center of each original edge, and then new edges are added to connect the new edge points to the new adjacent face points.
The positions of the vertices are calculated as follows:
The face points are positioned as the average of the positions of the face’s original vertices;
The edge point locations are calculated as the average of the center point of the original edge and the average of the locations of the two new adjacent face points;
The old vertices are repositioned according to the equation:
Q/N + 2R/N+S(n-3)/N
Q is the average of the new face points surrounding the old vertex,
R is the average of the midpoints of the edges that share the old vertex,
S is the old vertex point, and
n is the number of edges that share the old vertex. "
So what’s the deal? What is “TRUE catmull-clark”? Spline based? XDUGEF(hehe)?
What do you think? I know, long boring post…but I really think we need more elaboration…
MODS: I beg that this topic not be moved to the modeling section as I’d really like a wide survey of the CGTalk community. But of course, it’s your call.