NAME
p.vrml - output of VRML code from GRASS raster maps
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.
SYNOPSIS
p.vrml elev=name [color=name] output=name
Parameters:
- elev
- Name of elevation raster file to use for surface topography.
- color
- Name of raster file to use for surface color.
- exag
- Exaggeration factor for the vertical dimension.
- Default: 1.0
- output
- Name of 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.
NOTE
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/
TODO
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.
AUTHOR
Bill Brown, US Army Construction Engineering Research Laboratory