[X3D-Public] LOD versus GeoLOD

Joe D Williams joedwil at earthlink.net
Sat Nov 22 16:25:20 PST 2014

Hi Andreas,
may not help, but .zip is of some old .wrl LOD conformance test
All Best,

----- Original Message ----- 
From: "Andreas Plesch" <andreasplesch at gmail.com>
To: "X3D Earth Working Group" <x3d-earth at web3d.org>
Cc: <x3d-public at web3d.org>
Sent: Saturday, November 22, 2014 7:21 AM
Subject: Re: [X3D-Public] LOD versus GeoLOD

> 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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