Hi Sean,

You are correct the range distance of LOD's are in the LOD's own local
co-coordinate system.  This is appropriate as you almost aways want
LOD's to scale relative to a screen size, and doing the calc in local
coordinate allows you to decorate subgraphs with LOD's with transforms
that scale up or down the subgraph and still have the LOD ranges
computed appropriate for that new scaling.  This behavior is key to
get a scene graph to be well encapsulated.

It sounds like in your case you have transforms above your LOD's that
scale your objects, but you still want their ranges to set in world
coords, that ignore any transforms.  This would present the problem
that is the transforms scale change then the LOD would choose
different children - choosing an in-apprioriate level of detail for
the on screen size.


On Fri, Oct 9, 2009 at 5:21 AM, Sean Spicer <sean.spi...@aqumin.com> wrote:
> Studying the source a bit harder, I think the range-distance is
> definitely in Object (local) coordinate.  The distance calculation
> (osg::LOD.cpp) is:
> required_range = nv.getDistanceToViewPoint(getCenter(),true);
> where getDistanceToViewPoint is (osgUtil::CullVisitor.cpp)
> (pos-getViewPointLocal()).length()*getLODScale();
> So, this raises the question: is there a good reason why there is no
> option to specify the LOD range distance in World Coordinates?  This
> would make complex LOD graphs like the one I'm working on much, much
> simpler.  Perhaps there is another method that I just do not see?
> cheers,
> sean
> On Thu, Oct 8, 2009 at 10:50 PM, Sean Spicer <sean.spi...@aqumin.com> wrote:
>> This may be a simple question - is the LOD range distance specified in 
>> object or world coordinates?  I seems as if it should be in world 
>> coordinates, but I've got an example with numerous LOD nodes in sub-graphs, 
>> and if I sent a constant distance range in each of them (0.0, 30.0f) so that 
>> each LOD node has the same range - the LOD switch only behaves as expected 
>> if the transforms above each LOD node are identical.  The moment I have a 
>> scale matrix above the LOD the switch becomes dependent on the 
>> scaling...e.g. larger LODs switch before smaller ones.  This leads me to 
>> think that the LOD range distance is in object coordinates, and needs to be 
>> scaled by the localToWorld transform.
>> I've had a look at the source, and it seems logical (not to mention that I'd 
>> be shocked if someone hadn't had a problem before this if it were incorrect) 
>>  Comments?  Thoughts?
>> cheers,
>> sean
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