## Computer Aided Ferret Design

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.

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

 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.

 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.

 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.

 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.

### Results

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

 View from the side

 Compared to the patch pasted model, the new model is much better!

 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!