RE: ElevationGrid

["Braden N. McDaniel" <braden@shadow.net>]

> -----Original Message-----
> From: The Casteels [mailto:casteeld@cococo.net]
> Sent: Wednesday, March 11, 1998 7:31 PM
> To: Braden N. McDaniel
> Cc: Neil Woodhouse; www-vrml@vrml.org; geovrml@ai.sri.com
> Subject: Re: ElevationGrid
>
>
>
>
> Braden N. McDaniel wrote:
>
> > Why is this a limitation of the ElevationGrid node? This is the kind of
> > thing an authoring tool should do for you. You note that there are tools
out
> > there to create height field image files--it just as easy to go the
other
> > direction.
>
> Point taken, however if a widly accepted and successful way of doing
things
> exists, why not use it.

Because, while this general idea may be widely accepted, is there some
standard color-to-height mapping that will please everyone? Of course not.
So we would wind up just adding a lot of parameters to the node,
complicating things and bulking up the spec.

> An image file is already a rectangular grid,
> each pixel
> contains numerical information. They are compact and well known, and there
> are probably more tools available for working with image formats than
> text formats.

Conversely, the conversion program to convert colors to heights is trivial
to write. You could even do it in JavaScript if you wanted to confine
yourself to run-time calculation using PixelTextures.

> In addition, think of what you could do with an animated GIF if it
> was directly
> processed as a height field.

GIF support, remember, is not required for conformance. ;-)

This particular kind of thing would be rather difficult to implement from
the VRML side--but by no means impossible. The best way to do it would
probably be to pre-compute the sequence of heights, and "play" it
concurrently with the MovieTexture. Alternately, if on-the-fly calculation
is an absolute requirement (if you're dealing with real-time generated data,
for instance), you could probably have a Java Script node applet which would
"play" (but not render) the video clip concurrently with the MovieTexture in
the VRML world, generating the height values and sending them to the world
at each frame.

> As for authoring tools............ what's an authoring tool?    :-)

I tend to refer to anything that helps me create VRML and isn't a text
editor an "authoring tool." ;-) (Not that a text editor isn't an authoring
tool, too, in the strictest sense--just that the term brings slightly
higher-level tools to mind for me.)

Prismatic Booger
Braden N. McDaniel, braden@shadow.net
<http://www.shadow.net/%7Ebraden/>

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