[X3D-Public] LOD versus GeoLOD

[Andreas Plesch]

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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