NAME
          p.vrml - Translates to Virtual Reality Modeling Language
          (GRASS Map Output Program)

     SYNOPSIS
          p.vrml
          p.vrml help
          p.vrml elev=name [color=name] [exag=value]
                 output=name

     DESCRIPTION
          p.vrml outputs GRASS data in the format of Virtual Reality
          Modeling Language (VRML), for viewing on the World Wide Web.
          GRASS inputs are a raster map for representing terrain and
          an optional raster map for color to be draped over the
          terrain.

          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.

          A vertical exaggeration factor may be specified to
          compensate for elevation units which are different that map
          units, or to achieve better visualization results with flat
          terrain.


     COMMAND LINE OPTIONS
          Parameters

          elev 
               Raster file for use as elevation.

          color
               Raster file for use as color.

          exag 
               exaggeration
               default: 1.0

          output
               Name of new VRML file.  If the extension "wrl" (world)
               is not present it will be added.


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

          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.




     SEE ALSO
          http://vag.vrml.org/
          http://www.sdsc.edu/vrml/


     AUTHOR
          Bill Brown, UI GMS Laboratory