[X3D-Public] LOD versus GeoLOD

[Tom Sparks]

On 22/11/14 06:27, Andreas Plesch wrote:
> Hello,
> 
> I want to clarify my understanding of the GeoLOD node but I am
> struggling with how it improves on the regular LOD node. Here is what I
> currently understand. GeoLOD defines a single level of refinement by
> providing up to four children nodes (by URLs) which will be substituted
> for the main root node if the viewer gets closer than a range distance.
> A progressive tree of refinements can be achieved by making the children
> nodes themselves GeoLOD nodes. On the contrary, a LOD node defines
> multiple levels of refinement by providing a child node for each level
> which is then selected based on viewing distance. The idea is that a
> single child node covers completely the presented area. The child nodes
> are not specified by URL but are internal to the node. So there seem to
> be clear differences between GeoLOD and LOD nodes. However, since the
> LOD node definition is more general, it seems to me that GeoLOD node
> could be substituted functionally by a LOD node in this way. Given this
> GeoLOD node:
> 
> <GeoLOD range="100"
>   child1Url="child1url"
>   child2Url="child2url"
>   child3Url="child3url"
>   child4Url="child4url" >
> 
>    <Group DEF="rootNode">
>     <GeoElevationGrid />
>    </Group>
> 
> </GeoLOD>  
> 
> an equivalent LOD node may look like this:
> 
> <LOD range="100">
> 
>  <Group DEF="detail-tiles">
>   <inline url="child1url"/>
>   <inline url="child2url"/>
>   <inline url="child3url"/>
>   <inline url="child4url"/>
>  </Group>
> 
>  <Group DEF="root-tile">
>   <GeoElevationGrid />
>  </Group>
> 
> </LOD>
> 
> Here the LOD node simply just uses one range level, (instead of
> multiple), a group to define up to four child nodes and inline nodes to
> get the equivalent of the GeoLOD childUrl fields. The inlined nodes
> could include other LOD nodes in order to get a quadtree this way.
> Inline nodes would need to be able to load contained inline nodes which
> is something I am not sure x3dom.js at least currently supports although
> it may. Also the GeoLOD specification language is more specific about
> loading and unloading tiles. There are probably other differences which
> I am not seeing, so any comments would be helpful.
> 
> Thanks, Andreas
Geo LODing is known as Quad LODing, it is mostly used in virtual
terrains [1] https://www.youtube.com/watch?v=LxZhWrSmrOY
the LOD node is a discrete LODing

both of them suffer from popping[2]
> 
> 
>
[1] http://vterrain.org/
[2] https://en.wikipedia.org/wiki/Popping_%28computer_graphics%29
> _______________________________________________
> X3D-Public mailing list
> X3D-Public at web3d.org
> http://web3d.org/mailman/listinfo/x3d-public_web3d.org
>