Re: Help building paging ASD.

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Angus Dorbie (dorbie++at++sgi.com)
Wed, 03 Feb 1999 20:13:32 -0800

Yes I've seen this paper. After resolving texture stability during
geometric reduction it's main focus is geometric simplification while
using bump maps to preserve the original appearance/ normal data. It is
quite unrelated. There are some gouraud shading artifacts created when
you introduce a new vertex in a lit ASD terrain. There are ideas on how
to fix this, the current approach of introducing a coplanar vertex in
the middle of an edge and morphing to it's desired position won't do
since the initial step introduces a new lighting result and potential
visible shading anomoly.

Cheers,Angus.

Greg Harrison wrote:
>
> I'm not sure the extent to which it's of use, but did you see the paper
> presented at SIGGRAPH last year by UNC using a 'perturbation metric'?
> (Cohen, Olano, Manocha."Appearance-Preserving Simplification") It was
> related more to bump maps though and I think you're dealing more on a vertex
> basis.
>
> Greg
>
> We have experimented with different ways of morphing normals, none
> of them seems satisfying. You can see popping on the terrain
> because lighting is not continuous. Even if a per-vertex-per-face
> normal is used, doing normalizing normals in software is
> pretty expensive.
> This is why we didn't put it in the paging support for ASD.
> In libpfdu/pfdBuildASD.c, we gave an example
> of how the normals are generated and stored.
>
> Jenny Zhao zhz++at++engr.sgi.com 650 933-5091
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