[osg-users] adaptation of chunkLOD to OSG

Robert Osfield robert.osfield at gmail.com
Mon Sep 1 00:53:10 PDT 2008


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?

>> 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.



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