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Re: Computation of limit positions for triangle/quad by spliting and averaging (with facet traversal)

Posted by Scott Schaefer on September 05, 2005 at 10:54:51:

In Reply to: Re: Computation of limit positions for triangle/quad by spliting and averaging (with facet traversal) posted by Jianbing Huang on September 05, 2005 at 10:27:08:

: Thanks for the comments. You are definitely right that limit position/normal masks become quite complicated and the quad/triangle paper from stam/loop actually mentioned that they compute the left eigenvectors numerically for irregular configurations. Also I have not seen any work related to boundary/crease treatment for this scheme - assuming the treatment will be an extension to Zorin's treatment for loop/catmullClark the scheme will become even more complicated.

: Quite honestly from an application point of view, I am not sure if quad/triangle scheme competes well with a system with both loop and catmullClark schemes that are targeted at shapes of different characteristics.

Well, that was kind of the point of the triangle/quad scheme. The goal was to reproduce Loop subdivision on all triangles meshes, Catmull-Clark subdivision on quad meshes, and do something reasonable when you have mixed meshes. So the end goal was not to lose anything by moving to a tri/quad scheme except maybe simplicity of code.

However, you're right in saying that the places where the triangle and quad surfaces meet are somewhat complicated to deal with in light of all of the operations we come to expect from subdivision surfaces (exact limit/tangent, boundary rules, etc...). Research is hardly ever finished and I think there is room for more work to be done in this area.

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: : Thanks for the comments. You are definitely right that limit position/normal masks become quite complicated and the quad/triangle paper from stam/loop actually mentioned that they compute the left eigenvectors numerically for irregular configurations. Also I have not seen any work related to boundary/crease treatment for this scheme - assuming the treatment will be an extension to Zorin's treatment for loop/catmullClark the scheme will become even more complicated. : : Quite honestly from an application point of view, I am not sure if quad/triangle scheme competes well with a system with both loop and catmullClark schemes that are targeted at shapes of different characteristics. : Well, that was kind of the point of the triangle/quad scheme. The goal was to reproduce Loop subdivision on all triangles meshes, Catmull-Clark subdivision on quad meshes, and do something reasonable when you have mixed meshes. So the end goal was not to lose anything by moving to a tri/quad scheme except maybe simplicity of code. : However, you're right in saying that the places where the triangle and quad surfaces meet are somewhat complicated to deal with in light of all of the operations we come to expect from subdivision surfaces (exact limit/tangent, boundary rules, etc...). Research is hardly ever finished and I think there is room for more work to be done in this area.

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