Re: Double-Precision, Large-Area Databases, and SIGGRAPH

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Angus Dorbie (dorbie++at++sgi.com)
Tue, 04 May 1999 17:50:43 -0700

There's a slight problem with your original post Michael.

The notion that you can apply the chunk offset for each terrain cell in
method B without a matrix and therefore get bound box geoset culling is
wrong. It would require a lot of translations applied directly to the
vertices and infact these woiuld have to be applied instantly whenever
the eye origin changed.

Bottom line you need that single precision offset on the model matrix to
accomodate some variable delta between the eye and the terrain
reguardless of the scheme used.

Apart from this both suggestions are perfectly fine. In double precision
choose an offset near the eye and subtract that value from both the eye
and the model matrix, then cast to single precision. Operation A is a
subset of B where the exact eye point is chosen as the point near the
eye, it is however not significantly different.

Cheers,Angus.

You get away with no global offset but Michael T. Jones wrote:
>
> A week (or so) ago, someone asked about handling databases with large
> dynamic range. One of the responses mentioned an old email that I'd
> sent out years ago. I was looking for something in the info-performer
> archive just now and ran across the old article. Here it is for those
> who
> were looking for the information:
>
> http://reality.sgi.com/performer/perf-96-04/0269.html
>
> Michael Jones
>
> P.S. The SIGGRAPH part of the subject has to do with the fact that
> I was nominated to be treasurer of SIGGRAPH for the upcoming
> term. The ballots are in the mail to all members, and I'd
> appreciate
> your vote if you think I am qualified. The candidate
> information
> is at http://www.siggraph.org/elections/index.html. Thanks!
> ----------------------------------------------------------------------
> Michael T. Jones - mtj++at++intrinsic.com - Intrinsic Graphics Inc. - (650)
> 210-9933
>
> A frog in a well says "The sky is as big as the mouth of my well"

-- 
"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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