Re: Findin global vertex coordinates

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Angus Dorbie (dorbie++at++bitch.reading.sgi.com)
Sat, 6 Apr 1996 18:09:33 +0100

On Apr 5, 3:59pm, Allen Bierbaum wrote:
> Subject: Findin global vertex coordinates
>
> [ plain text
> Encoded with "quoted-printable" ] :
Here is my problem,
>
> I have a triangle in a geoset. I want to shoot rays out of the center
of the triangle in a hemispherical pattern, in order to see what polygons the
triangle can "see". To do this I find the center of the triangle and the
triangle's normal, and then construct a set of segments form this information.
 The problem is that I am intersecting the segments with the whole scene graph,
so since my triangle is below some DCS's, the center point in the global
coordinate system (at the root node) is different than my value. Because of
this, the intersection is being passed the wrong values. I believe that I need
to transform the segments into the global coordinate system before the
intersection.
>
> 1. Am I correct in my assessment of the problem???

I seems so.

> 2. How do I solve this problem??? (I know that I have to find the transform
matrix up to the triangle, but then do I multiply my segments by that matrix,
or it's inverse)

Construct the matrix (not the inverse) and call pfXformVec3() to transform the
vector to global coordinates.

> 3. How do I find this matrix knowing only the geoset the triangle is in???
(I can guarantee that geosets are not shared)

pfGetParent() for everything above the geode, but I don't see an easy way
of getting a geode from a geoset.

How did you get tour hands on the geoset in the first place? Can't you get the
Geode?

>
> Thanks in advance for any help
>
> -Allen
>
> ==============================
> Allen Bierbaum ISU Vislab - ISU CAVE
> allenb++at++iastate.edu
> RA - Carolina Cruz
> ==============================
>
>
>
>-- End of excerpt from Allen Bierbaum

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