Computer Aided Ferret Design

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My thesis topic was in tailoring Surface Pasting to create ferrets. Ferrets are small bundles of personality from the mustelid family. They have long narrow bodies that can assume almost any curved shape, so splines are the natural tool for modelling their bodies.

images/birch_sleeping.png

Previous techniques in surface pasting have the following problems that makes it hard to model ferrets:

  • pasting patches limits features to rectangular bumps, inadequate for modelling arms, legs, eyes or ears
  • the underlying rectangular structure of the feature is often visible
  • the feature warps to the curvature of the base surface, not always in a predictable way

images/ferret_old.png
Ferret modelled with patch pasting

Based on these observations, I improve modelling with surface pasting in three ways.

1. Projective cylindrical pasting

I created a projective interface for pasting generalized cylinders. The boundary points at the end of a cylinder are projected in the direction of the cylinder's spine to achieve approximate C0 and C1 pastes.

images/cyl_paste.png
Cylinder before pasting; approximate C0 and C1 pastes

This improvement allows me to build and paste arms and legs modelled with generalized cylinders. In addition, cylinders with concave cross sections can be pasted as well. And by trimming the outside of the base surface rather than the inside, we have an effective method of capping cylinders with concave cross sections.

images/ferret_cap.png
Approximate C0 and C1 capping of a cylinder with a ferret shaped cross section

2. Centroid projective patch pasting

I replaced the normal displacement patches with centroid displacement patches. Control points are displaced from a centroid which is used for pasting onto the base. All boundary points are projected according to the coordinate frame of the centroid, which also allows a somewhat unintuitive method of creating arbitrarily shaped boundaries. Because inner control points are displaced from the same location, the feature shape does not warp as much compared to standard pasting.

images/untrimmed.png
Compare to standard pasting (centre), centroid projective pasting (right) warps less

3. Trimmed patch pasting

I created the pasting of trimmed features. Patches are trimmed and a cylinder created to blend the feature onto the base. This allows easy creation of features with non rectangular boundaries such as eyes and ears.

images/trimmed.png

Results

The final ferret is created with cylindrical body and limbs, trimmed eyes and ears, and the limbs are capped for an approximate manifold.

images/ferret_pre.png images/ferret_post.png

images/ferret_side.png
View from the side

images/compare_old.png
Compared to the patch pasted model, the new model is much better!

images/compare_sprite.png
However, there is plenty of room for improvement before we approximate the real ferret.

And if we can model ferrets, we can model plenty of other things!

images/duck.png images/fish.png

Additional resources

Here are some things to read

Here are some talks to look at

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Last updated: Wednesday, 17 September 2003 @ 03:41:42 EST
ssiu_at_cgl_dot_uwaterloo_dot_ca