# Catmull-Clark Subdivision (Original Vertex)

Hi,

im having a little trouble with movie the original vertex, based on the algorithm:
http://en.wikipedia.org/wiki/Catmull-Clark_subdivision_surface

Assuming I have a quad of: (-1, -1, -1), (1, -1, 1), (1, 1, -1), (-1, 1, -1)

Now say i want to re-position the top left vertex (-1, 1, -1)

**The centroid of the face is: (0.0, 0.0, -1.0)

**The Valence is 2

**The Average Of mid points connection vertex is: (-0.5, 0.5, -1.0)

If i plug those into the formula i get:
vp = (([0, 0, -1] + (2 * [-0.5, 0.5, -1.0]) + ((2-3) * [-1, 1, -1] ))) / 2
= ([0, 0, -1] + [-1, 1, -2] + [1, -1, 1]) / 2
= [0, 0, -2] / 2
= [0, 0, -1]

This is not the correct position for the original point however.

Please can someone tell me where im going wrong?

Thanks,

Never mind

I’m not a wizard of catmull clark subdivision though I have implemented a test program…But one thing seems wrong on first sight: centroid is at (0,0,0). Other than that, no time to read wikipedia right now…

Its ok…

I figured out the problem. Catmull Clark Subdivision requires 2-manifold geomtery

Not necessarily.

You can still subdivide boundary edges to make them smooth using special cases.

Not necessarily.

You can still subdivide boundary edges to make them smooth using special cases.

use CGAL.

Not necessarily.

You can still subdivide boundary edges to make them smooth using special cases. [/QUOTE]

Can you please elaborate on these “special cases”?

Thanks,

Probably better to just convert your model into valid geometry, before trying to subdivide it:

You should be able to convert any nonmanifold geometry into 2-manifold geometry.