Re: Large Area Database

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Angus Dorbie (dorbie++at++sgi.com)
Mon, 26 Apr 1999 10:37:12 -0700

Rob Jenkins wrote:
>
> MLM Veraart wrote:
> >
> > Devrim Erdem wrote:
> > >
> > > Hi,
> > >
> > > I have a huge terrain database where I position
> > > tanks and aircrafts. The usual x and y are values
> > > like 300000. As I shall expect , there are jittering
> > > effects. Especially planting tanks using isectors cause
> > > really bad jitter effect.
> > >
> > > How can avoid these effects ?
> >
> > You have to move the viewer to the origin and translate the terrain
> > the same amount. Al calculations should be done in double and the
> > results put in the performer structures (float). There is a mail in the
> > archives describing this principle. I think it was Rob Jenkins who
> > wrote it. It should be in the 1996/1997 archives.
> >
>
> I think I was just re-posting stuff that Michael Jones wrote. I'm pretty
> sure Angus had some code/slides illustrating this for a Dev Forum once
> too, not sure if they're available....

This is one of those questions which keeps comming up and everyone has
had a bash at it at some point or other, you should check the archives.

I have a showcase presentation on this from maybe 2 years ago. At the
Dev forum Allan overran an intro to performer so I never presented it.
It has been presented elsewhere. It just explains the concept of eye
space and why this subtraction helps by keeping the numbers low in the
modelview matrix and vertices.

Cheers,Angus.

-- 
"Microsoft's system was like a forest that hadn't had a controlled
 burn in decades, just waiting for one person with a match to turn
 it into a disaster. Melissa was Microsoft's fault. They left their
 system wide open to this sort of abuse, they knew it could happen
 and did nothing." -- Bruce Perens


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

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