[osg-users] adaptation of chunkLOD to OSG

hannes_b at gmx.at hannes_b at gmx.at
Thu Sep 4 12:36:46 PDT 2008

Robert Osfield wrote:
> Hi Hannes,
> On Fri, Aug 29, 2008 at 8:27 PM, hannes_b at gmx.at <hannes_b at gmx.at> wrote:
>> someone from the project came up with this question:
> "the project" being??  Your own project?

The Combat Simulator Project

>>> I think this demo never became part of OSG, which is also what Robert
>>> states in his response to your question. Anyway, I don't get what
>>> exactly he's talking about in terms of the relationship between
>>> ChunkedLOD and osgDB::DatabasePager. The chunking aspect in
>>> ChunkedLOD refers to the fact the rendering algorithm divides the
>>> terrain mesh into individual chunks that can be sent to the gfx
>>> adapter separately, eliminating the need to re-build the whole mesh
>>> every time the camera perspective changes. In my understanding,
>>> osgDB::DatabasePager is used to load terrain tiles in a background
>>> thread, but is not directly to the actual rendering operations.
> DatabasePager only does loading of subgraps in a background thread,
> incremental compiling of OpenGL objects, merge of new subgraphs and
> deleting of expired subgraphs.   This is not equivalent to ChunkedLOD,
> rather just one component of such as system, although I'd guess
> DatabasePager is far more capable than most paging systems that you'll
> find on ChunkedLOD implementations.
> The division of the database up is pre-processing step that is done by
> VirtualPlanetBuilder, which builds a hierarchical tiled database.  VTP
> is extremely scalable and can terrabyte geospatial whole earth
> databases.  All the databases generated by VTB are viewable in OSG
> applications, with the DatabasePager managing the paging automatically
> for you, and either standard osg::Geometry/osg::StateSet/osg::Node
> subgraphs or osgTerrain based subgraphs handling the scene
> representation and rendering.   VTB is the only source tool of its
> kind as far as I'm aware.
> Put osgDB::DatabasePager and VTP generated databases together and you
> have something that is far more scalable and capable than a ChunkedLOD
> implementation.
> Robert.

originally someone did a test with photo realistic terrain.
video (40s):
High resolution (26 Mo) http://documents.cigognes.net/csp/csp-terrain-photo.avi
Low resolution (YouTube) http://fr.youtube.com/watch?v=1NlZoylXrlo

we are a little bit confused.

is http://www.openscenegraph.org/projects/osg/wiki/Support/UserGuides/osgdem what you mean or are we on the wrong way?

with VirtualPlanetBuilder you mean http://www.openscenegraph.org/projects/VirtualPlanetBuilder
with VTP you mean http://www.vterrain.org/
i did not find anything about VTB, is it a mistyped VTP?

thanks for your help in our confusion.

best regards

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