[osg-users] Update Optimization

Robert Osfield robert.osfield at gmail.com
Mon Jul 7 02:42:50 PDT 2008

Hi Joachim,

One can use a HeightField for terrain, and have an O(1) look up into
the height field, this is very fast, so it's a useful tool if it's
appropriate to your problem.  However, it's not a general purpose
solution, and not one that come from free when you create a database -
you'd have to go an populate the height yourself from your source
database, and if you are lucky this might just be a height field in
the first place.

More typical a database is polygonal based, using LOD's or PagedLOD,
with lots of polygonal culutral data in it.  The data might even be
whole earth database, so not even flat.  For this wide range of data
the best we can do is make the standard intersection routines that
work on polygonal dataset work faster, as this is just what I'm
working on.  It won't get as fast as using a HeightField, but it'll
close the gap substantially.


On Mon, Jul 7, 2008 at 10:27 AM, Joachim E. Vollrath
<vollrath at vis.uni-stuttgart.de> wrote:
> Hello to all in this thread,
> I have absolutely no terrain expertize and I don't know how OSG implements
> this, but just out of curiosity:
> Suppose you have terrain elevation stored in an image (in CPU memory) as
> well as normals.
> Given the 2d coordinate of an entity in elevation image space - wouldn't
> calculating the height and normal (resp. orientation) merely reduce to a
> bilinearly interpolated lookup in that image?
> I may be wrong, but shouldn't it be possible to get interactive update rates
> that way?
> Best,
> Joachim
> John Burgess wrote:
>> Hi all,
>> My viewer needs to support at least 400 entities running at 30 Hz.. My
>> entities are all moving tanks and I need to clamp them to the terrain using
>> an update call back in every frame, the frame rate will drop to 3 Hz when I
>> load 300 tanks with the update cycle taking up a huge amount of time. How
>> can I achieve 30 Hz for 400 entities and yet be able to clamp them to the
>> terrain?
>> Thanks,
>> John
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> --
> Dipl. Inf. Joachim E. Vollrath
> Visualisierungsinstitut der Universitaet Stuttgart (VISUS)
> web:   http://www.vis.uni-stuttgart.de/~vollrajm/
> mail:  vollrath at vis.uni-stuttgart.de
> phone: 49.711.7816.403
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