On Thu, 2007-01-25 at 11:04 +0100, Karsten Otto wrote:
> Am 24.01.2007 um 19:05 schrieb Peter Amstutz:
>
> > I agree. I have the book they published describing the COLLADA spec,
> > and intend to base the VOS 3D data models on COLLADA wherever it makes
> > sense, including physics parameters.
> > [...]
>
> I guess I'll have to chime in at this point...
>
> I only took a quick glance at COLLADA, but it struck me again as a
> format primarily intended to model the *appearance* of a scene,
> rathern than its semantics. In that it isn't much different from,
> say, X3D, only that it may have more up-to-date features such as
> physics, scripting, and shaders. So once again:
>
> A shaded ball on a shaded cylinder being transformed to bend slightly
> along the Y-axis is just that, it is NOT a tree bending in the wind,
> even if it *looks* like one.
>
> If you ever expect any kind of autonomous machine interaction with a
> VOS world, please design the 3D data model so that it can co-exist
> with a semantic data model. Even better, make the semantic entity a
> first-class memeber of the world, and put the appearance in a child
> (or even external reference), i.e.
>
> world ---member--> tree ---appearance--> (cylinder, sphere)
> world ---member--> house ---appearance--> (box, extruded triangle)
Why isn't this a job for a metadata spec? It seems to me that this kind
of semantic information is too application-specific to encode in the
structure of the file format itself.
Note that you can attach metadata to any node in X3D. I don't know what
the case is with COLLADA; however, you could also transmit such metadata
out-of-band.
The out-of-band solution has a couple of interesting qualities:
* It readily supports a notion of allowing the same scene to mean
different things to different clients.
* You could potentially define mappings from the semantic metadata
file format to multiple different geometry file formats. So the
same semantic data could be meaningful regardless of whether the
geometry was expressed in X3D, COLLADA, or whatever.
Anyone who's ever used HTML and CSS should be seeing an analogy here.
Whether the semantic metadata lives out-of-band or in the scene,
coupling the nature of its specification to that of the geometry seems
like the Wrong Way.
--
Braden McDaniel e-mail: <[EMAIL PROTECTED]>
<http://endoframe.com> Jabber: <[EMAIL PROTECTED]>
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