sascha <sas### [at] userssourceforgenet> wrote in
news:3f256c8c@news.povray.org: 

> You're right and I'm aware of this problem. I've taken two different 
> approaches to this problem for the next version of JPatch:
> 
> 1)
> Subdivide a 3-sided patch into 3 4-sided patches (like 5-sided patches
> will be subdivided into 5 4-sided patches). The new patches are formed
> by: 
> 
> * computing the center of the patch.
> * deCasteljau'ing the edges
> * Connecting the center with the mid-points of each edge
> 
> This works more or less for 5-point patches (I still have some minor 
> discontinuity problems, I think this is because the 5-point-patch is 
> somehow "overconstrained" and it's not clear to me how to exactly 
> compute the center-point - suggestions are appreciated :-)
> This works too for 3-point patches which connect only to 4-point
> patches but causes hughe problems when two 3-point patches meet.
> 

This is a vague idea, from a vague understanding, and you're probably 
already way ahead of me on this...

as I understand it, it is a fairly simple matter to subdivide a 4 point 
patch into two 4 point patches, by just substituting boundary points, 
with control points, and interpolating intermediate control points. 
(Which in itself would be a nice feature in a patch model, to arbitrarily 
subdivide a patch)

Anyways, with the paper on 3 5 and 6 sided patches, you are provided with 
mathematical definitions (A bit hard to swallow) for 3 and 5 points 
patches, along with patterns for control points. 

Couldn't the same principle for subdividing 4 point patches into 2 4 
point patches be applied here? You could start with a 5 point patch 
definition, and then subdivide into  5 4-point patches by substituting 
control points in the 5 point patch definition into boundary edges for 
new 4 point patches, and interpolate the individual control points in the 
same manner you would when subdividing a 4 point patch?

Stop me if this all sounds stupid, or obvious...

Post a reply to this message