Re: spheric projection.

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Angus Dorbie (dorbie++at++sgi.com)
Tue, 30 Jun 1998 13:57:29 -0700

Angus Dorbie wrote:
>
> Huse wrote:
> >
> > Hi pfFolks,
> >
> > We would like to project the Onyx2 output (2 channels) on a spheric
> > screen.
> >
> > It's necessarily to do any correction in Performer for avoid deformity
> > in the screen?
> >
> > What about the case of two planes projection screens with 120 degress
> > between them?
> >
> > What kind of correction may we do?
> >
>
> You need to apply distortion correction. Normally this is done by the
> projectors. It's the kind of question that if you need to ask your
> probably in trouble. A full understanding of this is a lengthy thing
> to convey.
>
> The key to solving this is choosing a design eyepoint w.r.t. the
> display, and then sending video to the projectors which matches
> the geometry of the area subtended by the projection resulting
> from that the design eyepoint.
>
> A test pattern is normally drawn which can be aligned to a
> physical test pattern on the display surface and the appropriate
> adjustment is then made to bring the virtual pattern in alignment
> with the physical pattern. Either in the I.G. or the projectors.
>
> Cheers,Angus.

More info:

I can supply distortion correction code to anyone who needs to
do this in Performer, or you could use something like Vega
which also supports distortion correction, or work with a
company like Equipe which has also implemented distortion
correction.

Distortion correction on an SGI involves image readback from the
framebuffer to texture memory in real-time then rendering
the new mapping using a deformed mesh of polygons.

The computation of the deformation is tricky and I have code
which does this for any display and projector configuration.

Cheers,Angus.

-- 
"Only the mediocre are always at their best." -- Jean Giraudoux 


For advanced 3D graphics Performer + OpenGL based examples and tutors:
http://www.dorbie.com/
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