[geovrml] Re: adding vrml geometry to geovrml scenes

[Martin Reddy <reddy@AI.SRI.COM>]

Hi Garry,

The tsmApi routines that build a multiresolution tiled representation of a
terrain model will always use the GeoElevationGrid node in order to store
the coordinates in their original coordinate system. Therefore, what gets put
into the file is actual UTM coordinates and each of these are converted to
geocentric coordinates by the GeoElevationGrid node when you first load the
scene. This means that the terrain will follow the surface of the earth and
you will be able to perceive the earth's curvature over a sufficiently large
extent.

If you are trying to add some UTM geometry to a scene, then you can either
use the GeoCoordinate node (in place or a standard VRML Coordinate node) and
build your geometry directly using UTM coordinates; or, you can just model
the geometry as a plain old VRML model and then georeference it to a UTM
location with the GeoLocation node (obviously the latter would be less
accurate over large distances).

The -utm switch is not supported any more - hence why it is not documented or
displayed as an option when you run make_geovrml with no options. This is a
throwback to the previous release when GeoVRML was not completed. Hence it
would just put the UTM coordinates into a standard VRML file. Now that the
GeoVRML 1.0 spec is available, we can things properly using the Geo* nodes.

BTW: the rotateYUp field is not implemented yet in the Java version from
www.geovrml.org (contributors welcome!). Haven't tried Cortona's support of
this node yet.

Cheers,

Martin.


On Wed, 17 Jan 2001, Garry Keltie wrote:
> Hi List,
> 
> Im trying to add some geometry which is located with utm coords
> (x=eastings y=elevation z=-northings) to a geovrml scene. 
> 
> I understand the geovrml scene to be oriented to reflect its "round
> earth" position on the globe, in geocentric coordinates. If I want to
> use the regular vrml browser fly and walk navigation I should
> (expensively) use the GeoOrigin's rotateYUp field.
> 
> There are a few things Im curious about though:
> 
> If I build a geovrml scene from tsmApi that is built to utm (using the
> distributed utilities), do I get a flat representation that has some
> "mean" point as a sort of normal for the orientation of the scene? or,
> does it somehow curve to a round earth representation? (precalculated or
> at runtime).
> 
> >From the above, if it is an oriented flat representation then would it
> be easy to calculate that orientation and use a simple transform at the
> top level to avoid the rotateYUp?
> 
> I tried building the tree with the make_geovrml "-utm" argument for an
> explicitly flat representation, it did build although crashes the
> browser on load. Im aware that its not an advertised argument but apears
> in the tsmParseVRMLArgs function. Do I need to play with the api to
> implement this option?
> 
> Failing all of that, is to geovrmlise a standard vrml scene (basically
> building volumes that are georeferenced by their coordinates in a known
> zone) my option? then , is there an an easy geovrml wrapper I can add to
> it?
> 
> Cheers
> 
> --
> Garry Keltie
> 
> garry.keltie@rmit.edu.au
> InteractiveInformationInstitute &
> School of Architecture and Design
> RMIT
> 
> 
> 

---------------------------------------------------------------------------
Martin Reddy                                   SRI International, AI Center
                                               Menlo Park, CA 94025-3493
reddy@ai.sri.com                               Tel : (650) 859-6468
http://www.ai.sri.com/~reddy                   Fax : (650) 859-3735