Alain <ele### [at] netscapenet> wrote:
> Chris B nous apporta ses lumieres en ce 2008/02/12 07:21:
> > "here_I_am" <nomail@nomail> wrote in message
> > news:web.47b1738e5f9a6c867b1612e30@news.povray.org...
> >> Hi everybody!
> >>
> >> I have this face scene,where I have to define different region based on
> >> the
> >> location on the face(Such as one region for nose other for lips..and so
> >> on) but
> >> the problem I am facing is that even though I know the coordinate for all
> >> the
> >> triangle in the scene file i don't know which one corresponds to which
> >> region
> >> and I can't do this randomly since scene file has 15000 triangles.
> >>
> >> I would appreciate if you guys could help me out here.
> >> Thanks
> >>
> >
> > The best approach depends on what you need to do with the different regions.
> >
> > I suspect that the most effective approach overall would be to use a
> > modeller (either the one you created the mesh in or another modeller that
> > can read the mesh) and split the object down into separate meshes for each
> > of the 'regions' you need to manipulate independently.
> >
> > Failing that, you can use CSG with meshes (so long as the mesh normals are
> > all ok). You may therefore be able to use objects to carve areas out of the
> > face and split it up in that way. For example, you could define a simple
> > squashed sphere and position it (using trial and error) to engulf just the
> > nose. You could then use a sphere with the same values in a CSG intersection
> > with the mesh to isolate the nose and manipulate it independently of the
> > rest of the face.
> >
> > If you only need to identify separate regions for texturing it is possible
> > to use CSG within an  'object' pigment, so you could define a texture that
> > corresponds to the regions that you identified by trial and error.
> >
> > If you only need to find points on the surface of the face (e.g. for
> > positioning eyelashes, glasses, a pipe or a hat) you could use the 'trace'
> > function. Once again this can be done fairly quickly with a little bit of
> > trial and error. Use 'trace' to locate a point on the surface somewhere near
> > where you want to be. Add a little sphere or a thin cylinder to your test
> > render and refine the trace parameters to home in on the points you need -
> > e.g. the bridge of the nose, the corners of the lips etc.
> >
> > Also, if you have development skills you could use your favourite computer
> > language to split the mesh up using mathematical rules that you could devise
> > based on the trial and error technique above.
> >
> > If you can give a bit more of an indication of what you need to do it'll
> > probably be possible to recommend a particular approach.
> >
> > Regards,
> > Chris B.
> >
> >
> If you use CSG to cut a mesh, you don't need the mesh normals to be correct, or
> even the mesh to be closed.
> You need a well behaved mesh if you use it to cut another object.
>
> --
> Alain
> -------------------------------------------------
> If you are good, you will be assigned all the work. If you are really good, you
> will get out of it.

Thanks Chris and Alain for the suggestion.

As Chris suggested I tried using Maya to Chop my scene into different region.I
succeed but it turns out that when I tried to render those scene(regions) in
pov-ray..they had different orientation and spatial coordinate.Thus that rules
out the idea of chopping in Maya.

To make this work I am using CSG, means hit and trial and am finding the
intersection of face and cylinders and by using different cylinders  I'll have
different groups. I guess this is what you guys suggested me.

Basically I have different albedo map based on the location on the face and have
to use Torrance-sparrow BRDF model and since different region have different
BRDF coefficient.I need to chop my scene in to different region.
I would appreciate if you add something to it.(Other than what I am doing to
make this grouping thing more efficient)

Thanx

Regards
Ran.

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