[X3D-Public] LOD versus GeoLOD

Andreas Plesch andreasplesch at gmail.com
Sat Nov 22 07:21:38 PST 2014

Thanks, Tom and Doug for your helpful answers. From what I could see in the
x3dom implementation there is some culling of the scene graph for LOD nodes
depending on distance, GeoLOD is currently not available. A small but
important feature of GeoLOD is that the reference (center) point from which
distances are measured can be provided in geographic coordinates. I think I
will put together a test scene to find out more on how LOD works  in x3dom.
 On Nov 21, 2014 3:27 PM, "Andreas Plesch" <andreasplesch at gmail.com> 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
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