Thom DeCarlo (trdecarlo++at++tasc.com)
Fri, 27 Mar 1998 13:06:15 -0500
Lee Willis wrote:
>
> >From: Jonas Andersson <jonasa++at++cs.umu.se>
> >To: info-performer++at++sgi.com
> >Subject: Constructing pfASD
> >Date: Friday, March 27, 1998 1:52 AM
>
> > Hi pfAll,
> >
> >From Performer Programmer´s Guide:
> >"LODs can be generated using simple adaptations of well-known,
> >non-uniform-tesselation surface subdivision algorithms."
>
> >I would like to construct LODs from a high resolution set of
> >triangles where certain features, e.g. outlines of areas like
> >lakes, glaciers, etc. should change at a slower rate across
> >several LODs than the number of triangles inside these areas.
>
> >Are there well-known algorithms solving this problem as well?
>
> No. :-( Constructing an ASD "bottom-up" (starting from the most
> detailed and working backwards) is a particularly thorny problem,
> one I was never able to crack adequately. This is because of the
> requirements of how an each LOD in an ASD must be connected to each
> other. It is much simpler to start with a coarse tesselation and
> subdivide it according to those rules than to start with a fine
> tesselation and merge those into coarser samples.
It might be simpler, but it makes the technology less than useless for
accurate terrain modeling. It becomes something to be _avoided_! Our
applications need to ingest sub-meter elevation post spaced data and we
want to smoothly reduce resolution as the viewer moves away from the
terrain. This seems to be exactly the opposite of the situation you
describe.
>
> >Are there any free/cheap libraries or source code supporting such
> >algorithms?
>
> None that I know of.
>
I thought there was something presented at SIGGRAPH'97 that addresses
this. (Sorry, I don't have the course notes with me.)
> >Thanks for any help!
> >
> > Jonas
>
> ------------------------------
> Lee Willis Virtual Landscape Dermatologist
>
> lwillis++at++terrex.com TERREX
>
Thom
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Thom DeCarlo * Off site contact info
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