[osg-users] dynamic LODs
Tomas Hnilica
does anyone know about dynamic Level Of Details implementation in OSG?
There are well described algorithms like several types of Hoppe's
Progressive Meshes or Garland's Quadric Error Metrics.
I am wondering if no one made an OSG implementation (or is there some
major problem for such dynamics in scenegraph?).
The chunkLOD by Vladimir Vukicevic referenced on vterrain.org is not
available.
Also the Demeter project is not available on
http://www.terrainengine.com, but I found it on
http://www.tbgsoftware.com/downloads.html. Anyway it's not a general
dymamic LOD, but it's mainly for terrains.
Many thanks,
Tomas
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Tomlinson, Gordon
We have used a Dynamic CLOD implementation in the past and it work quite
well on constrained datasets but at processing cost and does not scale
to larger datasets or dense data sets such as LIDAR based.
We are in the process of moving away from a dynamic clod implementation
to an a more traditional/style tiled based solution to handle the
unlimited elevation data we have to work with in the same way that we
can currently handle terra-bytes of imagery on the fly.
Gordon
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Gordon Tomlinson
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Email : gtomlinson @ overwatch.textron.com
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Robert Osfield
On Tue, Oct 14, 2008 at 2:07 PM, Tomas Hnilica
<tomas....@webstep.net> wrote:
> does anyone know about dynamic Level Of Details implementation in OSG?
The VirtualTerrainProject is based ontop of the OpenSceneGraph and
adds a number of CLOD techniques.
> There are well described algorithms like several types of Hoppe's
> Progressive Meshes or Garland's Quadric Error Metrics.
> I am wondering if no one made an OSG implementation (or is there some major
> problem for such dynamics in scenegraph?).
No problem in implementing them, but... these days CLOD is not as
compelling a solution than it once was. Paged databases scale much
better - for instance the combination of VirtualPlanetBuilder and OSG
is currently being used to generate and view multi-Terrabyte whole
earth databases.
> The chunkLOD by Vladimir Vukicevic referenced on vterrain.org is not
> available.
chunkLOD is not a CLOD implementation, it's a paged system, since the
OSG has paging built into and it has VPB to build databases you
basically have something like chunkLOD right out of the box, and in
system that is far more flexible.
> Also the Demeter project is not available on http://www.terrainengine.com,
> but I found it on http://www.tbgsoftware.com/downloads.html. Anyway it's not
> a general dymamic LOD, but it's mainly for terrains.
I never found Demeter to perform well so wouldn't recommend it so the
lack of availability of Demeter is probably not too much of a
hindrance.
Robert.
Tomas Hnilica
many thanks for your reply.
If I understand it right, the VPB creates a hierarchy of static LOD
nodes that are paged.
But is it possible to use the VPB for generation of such graph for
general datasets, not only terrain data?
I have an large triangle mesh on input, let's say in STL format (can
convert to OSG Geode or custom vectors).
How can I give such input to VPB and get an PagedLOD hierarchy osga on
output ?
Simply generate osga and put it as input file (is it the
vpb::Source::MODEL)?
In the osgdem source I see the line
osg::ref_ptr<osg::Node> node = osgDB::readNodeFile(fileName);
does it mean that the input file must fit into the memory to process it?
Many thanks,
Tomas
Robert Osfield napsal(a):
Robert Osfield
> many thanks for your reply.
> If I understand it right, the VPB creates a hierarchy of static LOD nodes
> that are paged.
That is correct.
> But is it possible to use the VPB for generation of such graph for general
> datasets, not only terrain data?
No. It's for handle geospatial imagery and DEMs only.
> I have an large triangle mesh on input, let's say in STL format (can convert
> to OSG Geode or custom vectors).
> How can I give such input to VPB and get an PagedLOD hierarchy osga on
> output ?
> Simply generate osga and put it as input file (is it the
> vpb::Source::MODEL)?
>
> In the osgdem source I see the line osg::ref_ptr<osg::Node> node =
> osgDB::readNodeFile(fileName);
> does it mean that the input file must fit into the memory to process it?
Well you can't do any geometry processing of the sort you are looking
for with VPB/osgdem.
Also readNodeFile only handles models that can fit in main memory.
If you want a general purpose LOD tool that handles source polygonal
data that is larger than what can fit in main memory then you'll need
to either find a specialist tool to do this or to write it yourself.