Re: [Algorithms] VIPM and UV texturing

[Charles B. <cb...@cb...>]

Let me just point out how a metric can detect these case automatically.
The basic error metric is something like "deviation from linear interpolation".
Hence, if you have a linear case of (a,b,c) and you're thinking of removing b,
then the error is (b - (a+c)/2).  This error is related to the second
derivative of whatever parameter you're measuring (eg. the curvature).  Hence,
if you have a triangle which is textured normally but highly tesselated, you
will get zero error, because even though the UV's are different, they differ in
a linear way, eg. there's no curvature in UV space.

However, where you have a reflection, the curvature is quite large.  For example,
if u = abs(x), then u'' = 0 for x != 0, and u'' = -1 right at x=0.  Thus, any
collapse away from x=0 will be free, and any collapse across x=0 will be highly
penalized.

Of course you're right that artist intervention will always be more precise (if
you have good artists!!), I just wanted everyone to be sure and understand that
a good collapse error metric is very important, and will give you much higher
quality meshes, by leaving the discontinuities in place where they're needed.

At 10:01 AM 8/9/00 -0700, you wrote:
>Now the problem as you would guess is you have the face with coordinates like (1,0) -----  (0,0) ---- (1,0).  Obviously more granular then that. There are no texture coordinate discontinuities so the algorithm says it is ok.  The surface of the face is roughly flat so the internal vertex and edges are good candidates for collapse.  However, you then get the nice situation of  (1,0) ------ (1,0).  Doesn't look so hot.  I have the artists tag reflected seam vertices as uncollapsable until very late in the order.

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Charles Bloom    cb...@cb...    http://www.cbloom.com