[osg-users] VPB & osgTerrain basic functionality

Robert Osfield robert.osfield at gmail.com
Sat Mar 21 05:16:01 PDT 2009


Hi Dario,

You analysis looks pretty reasonable.  Right now the only TerrainTechnique
provided is GeometryTechnique that is a brute force tessellation of the
height fields.  It is possible to implement your own TerrainTechnique to
implement algorithms such as CLOD but with modern hardware this isn't a
critical need, and in fact loading the CPU rather than the GPU is typically
the wrong thing to do these days, and brute force algorithms will produce
better performance/quality.

The paging system also reduces the need for CLOD alogorithms ans the LOD's
are built into the database by VirtualPlanetBuilder.  Paged database created
by VPB scales comfortably into the terrabyte range, whilest still rendering
at a 60hz at runtime, it also handles whole earth databases without skipping
a beat.  Very few CLOD implementations can come close to this scalability
and handling of whole earth coordinate systems + precision.

Robert.

2009/3/20 Dario Filipovic <tarqe39 at hotmail.com>

>  Hi all!
>
> I was wondering can someone give me a few hints on what to look for in VPB
> in sense of its functionality. I not sure for instance what happens when you
> push a image file trough osgdem. From what i see as a result it seems that
> heightmap image and texture get fragmented and put into hierarchical
> structure of nodes with different LOD(TerrainTiles). Files with different
> LOD are then used in paging mechanism to dynamicly load generated terrain
> fragments at runtime.Is this so? Does it mean that there are no algorithms
> such as ROAM used?
> ALso, i would like to be sure of what does osgTerrain do. Ive tried to read
> sources (Im not an experienced programmer ;)) and from what i see
> TerrainTechnique is used as an interface for real culling and updating
> functionality of terrain node, Locator is used as a coordinate system
> manager. osgTerrain seems to be a wrapper around a HeightField, and what ive
> seen from osgTerrain example it does not include any LOD functionality.
>
> Im sorry for swamping with questions and toughts, but there is little or no
> documentation about this, and understanding things by reading sources is
> very time-consuming. Im generaly interested in abstract models that are used
> in osgTerrain and VPB, more precisely in basic functionality guidelines, so
> i could at least make my way trough sources faster.
>
> Many thanks! :)
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