Assignment pa#5:
Explore the Behavior of Several Subdivision Schemes

Re-read the four papers on subdivision surfaces, and try these schemes and some other variants in a hands-on manner in a demonstration package written by Jordan Smith.

Use the SLIDE file CS284/CODE/subdivision.slf and test many of the subdivision schemes accessible from the menu that do NOT have the word "SELECTIVE" in their name. In particular take a close look at:

  1. SLF_SUBDIVISION_DOO_SABIN
  2. SLF_SUBDIVISION_CATMULL_CLARK
  3. SLF_SUBDIVISION_CORNER_CUTTING
  4. SLF_SUBDIVISION_CORNER_ROUNDING
  5. SLF_SUBDIVISION_CORNER_ROUNDING_LOOP
  6. SLF_SUBDIVISION_CORNER_ROUNDING_BUTTERFLY
  7. SLF_SUBDIVISION_CORNER_ROUNDING_ZORIN
  8. SLF_SUBDIVISION_CORNER_TRIANGLE_LOOP
  9. SLF_SUBDIVISION_CORNER_TRIANGLE_BUTTERFLY
  10. SLF_SUBDIVISION_CORNER_TRIANGLE_ZORIN


<< JORDAN -- update this please ...>>

To make this SLIDE program work on the NT machines, you will need to add a new environment variable:
(make sure the slashes are facing the correct way):
SLIDE_LIBRARY = S:/slide/lib

  1. Right click on "My Computer"
  2. Select "Properties"
  3. Click on "Advanced" tab
  4. Click on "Environment Variables"
  5. Under "User variables"
    1. Click "New"
    2. Set the variable name to "SLIDE_LIBRARY"
    3. set the value to "S:/slide/lib"
    4. click "OK"
Within this slide program, compare the capabilities of the various schemes to make smooth, evenly rounded objects with as few concavities as possible for convex starting objects. One of the tougher test objets is "gHexPrism1" because of the many coplanar facets and the sharp edges in the input net.

Do a qualitative examination on three different objects, one of which should be  "gHexPrism1", given in the starter file.
You can activate different objets by "un-commenting" different instance commands in lines 300-340 in the subdivision.slf file.
Pick a second object of your choice.
Check out the on-line SLIDE web page on Tcl-Packages, the "slideui", and "geometry.tcl" to learn more about these packages and the different objects. 
The third test object should be your own design of a genus 4 object.
Report your observations on these test runs..

As a second way of focusing on the capabilities of the different schemes -- and using very much what you may learn from the four papers -- consider the following task:
Assume you have given the 20 vertices of a regular dodecahedron and would like to have a very finely tessellated, sphere-like, subdivision surface that interpolates these 20 vertices. Try to do this with two different subdivision schemes: an interpolating one and an approximating one.
Which two schemes would you use ? -- Why ? -- How ?
Describe the initial control mesh complete with a value for the circum-radius for each of the chosen schemes. Discuss the trade-offs of the resulting surfaces. Provide 2 images that show the control mesh and a (reasonably) smooth version of the surface (i.e., don't push SLIDE to the limit ...).

Bring your reports to class on Wednesday 10/25/2003.