[osg-users] Orthographic projection and LOD nodes

Robert Osfield robert.osfield at gmail.com
Wed Apr 22 06:17:42 PDT 2015

Hi Mike,

Traditional LOD's are selected on distance range, which makes sense
for perspective projection, but for orthographic it doesn't make
sense.  Choosing LOD based on screen space would be appropriate for
orthographic projection.  I haven't personally tried it with PagedLOD
but in theory it should work.  It will require you to modify the
PagedLOD's on loading if they aren't set up for screen space
selection, as osgDB::ReadFileCallback could be used to process the
newly loading subgraphs.


On 22 April 2015 at 14:12, Mike Connell <michael.connell at gmail.com> wrote:
> Hi!
> I have a problem viewing a PagedLOD terrain database together with a
> top-down bird's eye orthographic projection.
> Since the tiles furthest from the center of the screen are further from the
> eye point, they are rendered at a lower LOD level (the database uses the
> DISTANCE_FROM_EYE_POINT RangeMode). What I would like to achieve is a
> constant LOD scale across the entire view for a given ortho zoom level /
> "height".
> Has anyone come across - and solved this problem before?
> My idea so far involves fiddling with the CullVisitor - basically
> counteracting the effect of the distance to eyepoint calculation by
> modifying the LOD bias in the opposite direction. I am not 100% sure this is
> feasible, or necessary, or ideal.
> Is there a simpler solution?
> Thanks!
> Mike
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