Re: 3 channel projection system

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Greg Larson (gregl++at++dataserv.dayton.sgi.com)
Thu, 21 May 1998 16:45:10 -0400


Eric Brandwine wrote:
>
> We have a medium fidelity cockpit simulator, and have just ordered a
> number of hardware upgrades.
>
> We currently have an Onyx Reality Station w/MCO, driving 3 projectors
> on an ~150 degree arc. The projectors display on 3 flat screens,
> like \_/.
>
> We just ordered an Onyx2 IR w/DG8, 3 new projectors w/contrast
> modulation, and a single curved screen. We want to do edge blending,
> but are not sure of a couple of things.
>
> 1) Can the DG8 lay out channels in any geometry? The MCO would allow
> you to pick resolution/channel count, but you were stuck with the
> layout they gave you (to fit in a 2kx2k virtual buffer).
>
> We run 3++at++960x680, with 3 screens tiled horizontally, while the 3
> channels are tiled vertically.

Take a look at the ircombine utility in /usr/gfx. This is a gui tool to
help with channel layout. You can also do some edge blending with the
projector alignment and tuning depending on the projector.

>
> 2) How should we set up Performer to drive this projection system?
> Right now, we have 3 channels defined, with the center as the
> master, the 2 side channels offset ~50 degrees. This means 3
> rendering passes for our single pipeline. Is there any way that we
> could define a single channel with a 150 degree field of view, and
> divide it across 3 outputs of the DG8? Also, how should we get
> edge blenging working? Right now, the 3 channels that we are
> displaying are not co-planar, so even if we were to increase the
> horizontal field of view per channel a bit, and overlap the
> projected images, the overlapped region would not match due to the
> different geometries. Is this acceptable? Is there some way to
> tell Performer to make some number of pixels on the edge of the
> channel the same as the next channel over?

Ircombine will help with your channel layout and allows for an easy way
to overlap the output channels. Ircombine is also discussed in the
Onyx2 online mannuals.

I think your observations are correct regarding distortion in trying to
draw one large field of view. The effects of this will depend on the
curvature of your screen. This can be traded off depending on the
accuracy/fidelity for your simulation to meet target requirements.
There is a method used in S/W distortion correction to render a scene in
the first pass and then read back the frame buffer and map back onto a
set of polygons virtually representing your screen and sending only this
final scene to the DG.

You may find some related demo code at www.dorbie.com

>
> Any help would be appreciated!
>
> thanks,
>
> ericb
> --
> Eric Brandwine, Systems Engineer
> EricB++at++Mitre.org
> The MITRE Corporation, McLean VA 22102
> (703) 883-3319 FAX: (703) 883-1917
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-- 
Greg Larson     (937) 258-5247	*    
Silicon Graphics/Cray Research	*The conscious mind uses 2000 neurons
Systems Engineer->VisSim Focus	*The unconscious mind, 4  Billion 
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email: gregl++at++dayton.sgi.com	* 	

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