Re: [Algorithms] Articulated LOD

[Zhang Z. <zh...@gm...>]

Galand's method is easy to implement. the basic idea is to contract triangle
edges that have least impact on mesh deformation.

If you dont want to deal with it yourself, I believe 3dsMax has something
similar that can generate lower resolution meshes. so just pass it on to
your artists...



On 5/31/07, Matt J <mjo...@gm...> wrote:
>
> How do modern and semi-modern games handle articulated (bone/skin
> models) level of detail? To be more specific, you have a high polygon
> skinned mesh and you want dynamically reduce it and have a new
> skeleton map on the new mesh.
>
> I'm looking to be designing a new engine soon for work..but in this
> sense it will be focusing on character animation and rendering.
>
> I guess what it boils down to is you have Hoppes work and Garlands
> work in CLOD, or you have simply a set of N discrete LOD models. Here
> I'm interested in from a geometry standpoint in an immersive
> enviornment, obviously shader LODs and stuff are easier to implement.
>
> The truth is this stuff looks amazingly hard to implement any of the
> CLOD algorithms, at least for someone with not much experience
> (raising hand).
>
> The algorithms introduce new topics such as - energy minimization,
> eigenvalues (possibly), least squares optimization, quadric error
> metrics, and other moderately scary terms. I even heard someone said
> something about Clifford algebra to extend the equation of a line to N
> dimensions to handle attributes for Garland (!!) Then he said
> something that Garland isn't esoteric and easy to implement..well
> damn, if that's easy... what's hard? :-) Then you have the practical
> issues, triangle folding and other things to worry about even when
> implementing the simplest of operators. I assume if you look at
> everything in isolation and bite-sized pieces it is all doable, but
> taken as a whole it seems quite formidable.
>
> However, with discrete LOD I could see there being a problem with
> popping. Hoppe's discusses "geomorphing" but I'm not sure how that can
> be done without a progressive structure (because you geomorph between
> edge collapses and have the transition information there, but between
> two arbritrary meshes I can't see it knowing how to transition
> easily). Only recently in '04 was there actually some sort of paper
> for mapping skeletons onto reduced meshes. It also doesn't look like
> the ID3DX data structures for progressive meshes handles skinned
> meshes on articulated models, not without recreating the progressive
> mesh again.
>
> I'm curious how games handle Level of Detail for articulated meshes
> from a geometry standpoint, and good strategies for learning LOD .. I
> have the LOD book, but it is pretty sparse in math. The Ph. D papers
> are hard to understand, and the source code is too. Assume I had to
> implement a series of progressively harder algorithms to work my way
> up to articulated LOD, what would those be?
>
> Matthew
>
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