28 Aug 1996

This is a preliminary release of "p.vrml", a GRASS program
to output GRASS data in the format of Virtual Reality Modeling
Language (VRML).  

For further information about VRML and available viewers
for various platforms, see:
    http://vag.vrml.org/
    http://www.sdsc.edu/vrml/

This version only outputs raster maps in VRML 1.0 format.  
The newer VRML 2.0 format will be more efficient for geographic 
applications, as it introduces an "ElevationGrid" node so that 
only the elevation points will have to be written instead 
of the whole geometry.  The vast majority of VRML viewers 
currently only support VRML 1.0.

Future plans for this module are to allow draping of sites
objects and vector files and using the new sites format 
available in floating point GRASS to embed WWW links into 
site objects.  It will also be upgraded to support VRML 2.0
and will allow entering multiple preset "views" using the 
existing GRASS 3d_view file format.

Other possible additions: 
    o Allow animation of elevation, color, or sites based on 
      user interaction.
    o Degradation of the raster to produce TINs for improved
      performance.


This code should compile on any GRASS platform with either
GRASS 4.1 or floating point GRASS.  

For GRASS program installation instructions see:
http://www.cecer.army.mil/grass/faq-misc/install.html

-------------------------------------------------------------

Usage:
 p.vrml elev=name [color=name] [exag=value] output=name

Parameters:
    elev   Name of elevation file.
   color   Name of color file.
    exag   exaggeration
           default: 1.0
  output   Name of new VRML file.

"elev" is a raster file to use for surface topography.

"color" (optional) raster file to use for surface color.

"exag" is an exaggeration factor for the vertical dimension.

"output" is a name for the new VRML file.  If the extension
         "wrl" (world) is not present in the name, it will be added.

WARNING: VRML is not well suited for large geometrys which can
	 result from even a small geographic region.  Most viewers
	 seem to bog down with more than 12,000 polygons, depending
	 on your hardware & specific viewer.  Each grid cell results 
	 in two polygons, so a reasonable size region would be 
	 something less than about 75x75.  For improved performance
	 and smaller file size, leave off a color map.  Since VRML
	 is ascii text, gzip works very well to significantly
	 compress file size.

BUGS:  Currently the region is transformed to a unit size, so
       real geographic location is lost.  Side effects when
       working in a lat-lon location are that besides general
       distortion due to projection, a very small exaggeration 
       factor (on order of .001) must be used to compensate for
       vertical units expected to be the same as map units.


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Bill Brown				e-mail: brown@gis.uiuc.edu
220 Davenport Hall - MC 150             phone:  (217) 333-5077
607 S. Mathews                         
Urbana, IL 61801                      

	    http://www.cecer.army.mil/grass/viz/VIZ.html
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