Re: ElevationGrid II

["Yvan G. Leclerc" <leclerc>]

Gavin,

  Having double-precision coordinates would make life immeasurably simpler for
some of us folks using VRML for large geographics areas.  Currently,
single-precision coordinates require us to define at least three classes of
local coordinate systems for points on the globe: 

o a global geocentric system (origin at the center of the earth), but only
accurate to a few meters with single-precision floats;

o a local coordinate system for each 1 degree lat x 1 degree long cell
(accurate to .1 meters or so)

o a local coordinate system for each 1 km x 1 km cell (as accurate as we need!)

  So, if there's any way that we can get double-precision coordinates, that
would be wonderful!!

  We're also very interested in at least two geodetic coordinate systems:

   lat-long 
   Universal Transverse Mercator (UTM)

  Ralph Toms, of SRI, is currently working on a library for doing high-speed
conversion between such coordinate systems.  See
http://www.ai.sri.com/geovrml/vrml98/toms for more information, or send mail
to myself or Lee Iverson (leei@ai.sri.com).

Yvan

Gavin Bell wrote:
> 

> 
>   -- Double-precision coordinates (DoubleCoordinate maybe?) to support CAD
> applications that require very-high-precision models.  I'm suprised a
> VRML-For-CAD working group hasn't started to talk about this, and about
> adding trimmed NURBS and other features common to CAD applications.
> 
> Since you posted to the geovrml newsgroup, I assume you're interested in
> spherical coordinate systems that would be more appropriate for
> representing geographical features.  I haven't heard of anybody proposing
> or implementing such extensions (SphericCoordinate maybe?).
> 
> --
> Gavin Bell (gavin@wasabisoft.com)
> SkyPaint: what do QuickTimeVR, 3DStudio and VRML have in common?
>   http://www.wasabisoft.com/

-- 
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Yvan Leclerc                                              \ \  / /
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mailto:leclerc@ai.sri.com http://www.ai.sri.com/~leclerc/      /
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