Re: GIS

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Phil Keslin (philk++at++cthulhu.engr.sgi.com)
Fri, 03 Sep 1999 13:41:16 -0700

"Spann, Joseph R" wrote:
>
> Well it's still not clear to me. You've explained what Performer
> does and the complexity and why it's hard etc. But I've yet to
> glean any understanding of what specific hardware feature must exist
> to accomplish all this. Sorry but saying you can only do it on
> IR is not enough. What "Hardware" is missing from an Octane or an O2
> that prevents clip-mapping. Is it a systems thing or is there some mystical
> clip-mapping asic?

The ability to calculate the finest available LOD given an incomplete or
clipped mipmap is what's missing in other hardware implementations. The
hard part is not using the hardware that is actually pretty straight
forward. The difficulty is the data and system load management that has
to go with clipmapping to make it effective in a real-time application.
That is Performer's value add to clipmapping.

There is a write up on clipmapping and how it works titled "The Clipmap:
A Virtual Mipmap" by Tanner, Migdal and Jones in last years "Computer
Graphics Proceedings, 1998." It does a good job describing what has to
happen to make the technique work and some of its benefits.

- Phil

-- 
Phil Keslin <philk++at++engr.sgi.com>

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