On triangle quad subdivision scott schaefer and joe warren tog 22 1 28 36 2005
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On Triangle/Quad Subdivision Scott Schaefer and Joe Warren TOG 22(1) 28 – 36 , 2005. Reporter: Chen zhonggui 2005.10.27. About the authors. Scott Schaefer: B.S in computer science and mathematics, Trinity University M.S. in computer science, Rice University

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On triangle quad subdivision scott schaefer and joe warren tog 22 1 28 36 2005

On Triangle/Quad SubdivisionScott Schaefer and Joe WarrenTOG22(1) 28–36, 2005

Reporter: Chen zhonggui

2005.10.27


About the authors
About the authors

  • Scott Schaefer:

    • B.S in computer science and mathematics, Trinity University

  • M.S. in computer science, Rice University

  • Ph.D. candidate at Rice University

  • Research interests: computer graphics and computer-aided geometric design.


About the authors1
About the authors

  • Joe Warren:

    • Professor of computer science at Rice University

    • Associate editor of TOG

    • B.S. in computer science, math, and electrical engineering, Rice University

    • M.S. and Ph.D. in computer science, Cornell University

  • Research interests: subdivision, geometric modeling, and visualization.


Outline
Outline

  • Preview

  • Previous works

  • Catmull-Clark surface

  • Loop surface

  • Triangle/Quad Subdivision

  • On triangle/Quad Subdivision

  • Conclusion




Previous works
Previous works

  • Chaikin, G.. An algorithm for high speed curve generation .Computer Graphics and Image Processing, 3(4):346-349, 1974

  • E. Catmull and J. Clark. Recursively generated B-spline rurfaces on arbitrary topological meshes. Computer Aided Design, 10(6):350–355, 1978

  • D. Doo and M. A. Sabin. Behaviour Of Recursive Subdivision Surfaces Near Extraordinary Points. Computer Aided Design, 10(6):356–360, 1978


Previous works1
Previous works

  • C. T. Loop. Smooth Subdivision Surfaces Based on Triangles.M.S. Thesis, departmentof Mathematics, University of tah, August 1987

  • Stam, J., and Loop, C.. Quad/triangle subdivision. Comput. Graph. For. 22(1):1–7, 2003

  • Levin, A. and Levin, D.. Analysis of quasi uniform subdivision. Applied Computat. Harmon. Analy. 15(1):18–32, 2003


Previous works2
Previous works

  • Warren, J., and Schaeffer, S.. A factored approach to subdivision surfaces. Comput. Graph. Applicat. 24:74-81, 2004

  • Schaeffer, S., and Warren, J.. On triangle/quad subdivision. Transactions on Graphics. 24(1):28-36, 2005


Catmull clark surface e catmull and j clark 1978
Catmull-Clark SurfaceE. Catmull and J. Clark, 1978

New face point

New edge point

New vertex point

Standard bicubic B-spline patch on a rectangular control-point mesh


Catmull clark surface on arbitrary topology
Catmull-Clark Surface on Arbitrary Topology

  • Generalized subdivion rules:

  • New face point: the average of all he old points defining the face.

  • New edge point: the average of the midpoints of the old edge with the average of the new face points of the faces sharing the edge.

  • New vertex point:

After one iteration

Extraordinary vertex

(not valence four vertex)


Factorization
Factorization

Step1. Linear subdivision

Step2. Weighted averaging

Averaging mask for regular vertex


Centroid averaging approach
Centroid averaging approach

(b) Averaging the centroids

(a) Computation of centroids


Subdivision matrix
Subdivision Matrix

V

One-ring neighboring vertices of extraordinary vertex V

M: a constant matrix


Property
Property

  • continuous on the regular quad regions.

  • continuous at extraordinary vertices.


Loop surface c t loop 1987
Loop SurfaceC. T. Loop, 1987

Extraordinary vertex

(not valence six vertex)

Original mesh

Applying subdivision once


Loop surface
Loop Surface

(1) Averaging mask for regular vertex

(2) Averaging mask for extraordinary vertex ?


Centroid averaging approach1
Centroid averaging approach

(a) Centroid calculation for triangles

(b) The result averaging mask


Property1
Property

  • continuous on the regular triangle regions.

  • continuous at extraordinary vertices but valence three vertices (valence three vertices are only ).

Demo


Drawbacks of above surfaces
Drawbacks of above surfaces

  • Catmull-Clark surfaces behave very poorly on triangle-only base meshes:

A regular triangular mesh (left) behaves poorly

with Catmull-Clark (middle) and behaves nicely with Loop.


Drawbacks of above surfaces1
Drawbacks of above surfaces

  • Loop schemes do not perform well on quad-only meshes.

  • Designers often want to preserve quad patches on regular areas of the surface where there are two “natural” directions.

  • It is often desirable to have surfaces that have a hybrid quad/triangle patch structure.


Triangle quad subdivision stam j and loop c 2003
Triangle/Quad SubdivisionStam, J. and Loop, C., 2003

1. Initial shape

2. Linear subdivision

3. Weighted averaging


Averaging masks
Averaging masks

Averaging mask for regular quads

Averaging mask for regular triangles


Averaging masks1
Averaging masks

(a) Averaging masks for ordinary quad-triangles

(b) Averaging mask for extraordinary vertex?


Weighted centroid averaging approach
Weighted centroid averaging approach

(a) Centroids are weighted by their angular contribution

(b) The result averaging masks


Property2
Property

  • continuous on both the regular quad and the triangle regions of the mesh.

  • but not continuous at the irregular quad and triangle regions.

  • Cannot be along the quad/triangle boundary.

Demo


On triangle quad subdivision
On Triangle/Quad Subdivision

The unified subdivision scheme

  • “Unzips” the mesh into disjoint pieces consisting of only triangles or only quads. (Levin and Levin [2003])

  • Linear subdivision.(Stam and Loop [2003])

  • Weighted average of centroids. (Warren and Schaefer [2004])


Unzipping pass
Unzipping pass

  • Identify edges on the surface contained by both triangles and quads.

  • Apply the unzipping masks ( , ) to this curve network.

  • Linear subdivision.

  • Weighted average of centroids


Property3
Property

  • continuous on both the regular quad and the triangle regions of the mesh.

  • continuous along the quad/triangle boundary.

  • continuous at the irregular quad and triangle regions.


Conclusion
Conclusion

  • We have presented a subdivision scheme for mixed triangle/quad surfaces that is everywhere except for isolated, extraordinary vertices.

  • The method is easy to code since it is a simple extension of ordinary triangle/quad subdivision.