[osg-tds] osgTDS with coordinatesystemnode and large geocentric Databases

[Don Burns]

Hi Torben,

On Fri, May 22, 2009 at 7:39 AM, Torben Dannhauer <torben at dannhauer.info>wrote:

>  Hello,
>
>
>
> I discovered osgTDS for terrain modification and have some trouble to get
> it working.
>
>
>
> I got the source, compiled it and integrated the files into my OSG
> installation.
>
> osgTDS with the example data works great and has an impressive output.
>
>
>
> Unfortunalety osgTDS seems not to work with my geocentric database (WGS84)
> which I build with VirtualPlanetBuilder.
>
> During the application startup a message is displayed, that the model is
> not or not completely over Terrain:  “Terrain Deformation Software:  ERROR
> in Target Database Base definition:  at least one target is not completely
> over terrain.”
>

SO you understand the historical implications, VPB is a newer product than
osgTDS, and osgTDS has not been kept up with advances in osg, which would
explain the difficulty you've had with integration.  osgTDS is a community
supported project by design, so your work with it could be valuable in
keeping it up to snuff.

The message you are getting is undoubtedly (I haven't looked at the code for
about two years), the result of your models being in a different coordinate
space than the terrain over which they are positioned.  I would guess that
the solution is to use the same sort of coordinate node provided by OSG to
position your models.

There may be another consideration, in that osgTDS makes some assumptions
about "which way is up", or more specifically, "which is the bottom of the
models", and may require some transformations to get things right.... (I'm
not sure here, just guessing).

> I have read the Documentation but there are still some beginner questions:
>
> 1.       The osgTDS loader seems to load all targets mentioned in the .tds
> file by himself. Is it possible to relocate this models in my scenery to
> their right place and the terrain will always be corrected the right way?
>
I believe that we are on the same page here regarding my first paragraph.
You probably need to group your models under a coordinate system node.
However, you may also need to build the support for the coordinate system
node into the osgTDS traversers, as this node did not exist when osgTDS was
written.

> 2.       How is the loading logic build? Which model/target is
> parent/child of which other node, and at the end of the loading process,
> which node is passed back to the application as “loaded model” ?
>

There is nothing unique about osgTDS in the file loading.  it works like any
other osg viewer in that all objects listed on the command line are grouped
under a group node which is then formed as part of the main scene graph.
This is not unique to osgTDS.  The tds loader accepts a file named *.tds,
then uses the information therein to find the other components, which need
to preceed it on the command line.  It then divides the scene graph into
"Terrain" and "Targets", manipulates the coordinates of the terrain
according to the position of the targets.

> 3.       Is there any maximum or minimum distance up to which the terrain
> will be corrected to “touch” the target?
>
The software is designed to always connect to the target's "bottom", which
is assumed to be coordinates of the "bottom hull", formed by the coords with
lowest "z" value.  If you want to alter the behavior, you can insert targets
that are used for manipulating the terrain, but not drawn.

> 4.       Is it possible to use osgTDS for loading highdetail terrainmodels
> into larger low-detail, and osgTDS will adapt the low-level model that there
> is no z-fighting or things like that? Or is it better to use osgEarth for
> that purpose?
>
I have no idea what osgEarth is.  But yes, osgTDS does, in fact, adapt the
lower level model to the new set of coordinates.  This allows you to shape
the surface of the terrain to your liking.

> 5.       Is it possible to use osgTDS in combination with osgEarth? Both
> projects seem to use a loader-plugin over osgDB.
>

Again, I have no idea what osgEarth is.  osgDB and "loader-plugin" however
are not mutually exclusive.  osgDB is the framework by which osgTDS and
other plugins work.

-don

>
>
> Thanks for your help,
>
>
>
> Torben
>
>
>
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