Re: Picking with asymmetric Viewing Frustum

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Angus Dorbie (dorbie++at++sgi.com)
Tue, 03 Nov 1998 10:54:57 -0800

It's a really simple matter to compute the right intersection vector
given
a frustum and orientation matrix.

I posted some code about 3 (?) years ago for this. If you search the
archives
you should find it.

Cheers,Angus.

Wolfgang Trog wrote:
>
> Hi Marc and all Performers,
>
> there was a related question in a mail in september (see
> http://reality.sgi.com/performer/perf-98-09/0153.html). It seems that picking in an
> orthogonal frustum will be implemented in Performer 2.2.3. Will this version allow
> to do picking in an asymmetric frustum, too? Perhaps, somebody at SGI can clarify
> this ?
>
> Thanks,
>
> Wolfgang
>
> Marc Erich Latoschik wrote:
>
> > Wolfgang Trog wrote:
> > >
> > > I try to do picking in a channel with an asymmetric viewing frustum. The
> > > viewing frustum is set by pfMakePerspChan. E.g. to values 30 deg to
> > > left, 32 deg to right and 22.5 top and bottom. Then, I do picking with
> > >
> > > NrHits = pfChanPick( Channel,
> > > PFPK_M_NEAREST |
> > > PFTRAV_IS_PRIM |
> > > PFTRAV_IS_PATH |
> > > PFTRAV_LOD_CUR,
> > > ChannelX, ChannelY, 0.0f, PickList );
> > >
> > > The picking calculation seems to use only the smallest value of
> > > right/left and top/bottom. So the picking results are shifted to the
> > > left/right and top/bottom. In case of my example, the picking results
> > > are shifted to the right (looks like a 2 deg shift).
> > > When I supply symmetric values to pfMakePerspChan, this works fine.
> > >
> > > Can anybodye help me ?
> > >
> > Yes and no Wolfgang ;),
> > sorry the answer comes late, but im currently running into the same
> > problem.
> > To disaapoint you, read the relnotes of Performer 2.2
> > under the section Bugs and Workarounds it is said that picking
> > in an asymetric frustum is not currently supported.
> > Sorry for that.
> > I still try to figure out how to do it. Right now it seems that the only
> > possibility is to hold all scene geometrie in a seperate process and to
> > apply object and viewpoint transformation on my own. :( That is of
> > course
> > the worst thing but i have no other ideas...
> >
> > Does anyone have a good one for that problem?
> >
> > bye
> >
> > Marc
> >
> > ********************************************************************************
> > Marc Erich Latoschik, AG-WBS, Technische Fakultaet der Universitaet
> > Bielefeld
> >
> > Universitaetsstrasse 25
> > Postfach 100 131
> > 33501 Bielefeld
> > Raum M4-122
> > Fon: (0521) 106 2919
> > Fax: (0521) 106 2962
> >
> > marcl++at++techfak.uni-bielefeld.de
> > http://www.TechFak.Uni-Bielefeld.DE/techfak/persons/marcl/
> > ********************************************************************************
>
> --
> _______________________________________________________________________________
>
> In every hierarchy the cream rises until it sours.
> -- Dr. Laurence J. Peter
> _______________________________________________________________________________
>
> Wolfgang Trog phone : (+49) 89/321407-31
> Philosys Software GmbH fax : (+49) 89/321407-12
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> 85716 Unterschleissheim http://www.philosys.de
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"Only the mediocre are always at their best." -- Jean Giraudoux 


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