[osg-users] How should I organize the scene graph to handle 2 million points and lines?

J.P. Delport jpdelport at csir.co.za
Tue Nov 3 22:31:53 PST 2009


Andrew Burnett-Thompson wrote:
> Sorry to butt in the conversation here, but I also am working on an app 
> with memory issues and we are considering Paged LOD. 
> For a scene with millions of objects, won't there be a huge performance 
> hit as geometry is loaded/unloaded? 

possibly, but if you can't fit everything into memory at once you have 
to load/unload something. The PagedLOD is able to cope with terabyte 
sized terrain databases with millions of files at interactive rates, so 
it seems possible.

> I imagine the sort of scene like a city scape where detail is controlled 
> very nicely. That's good as occlusion means not too many things will be 
> visible at any one time. 

Yes, it also helps when e.g. 95%+ of an earth database is outside the 
field of view and can be culled :)

> However what in the case of points and lines as the user above has 
> posted? Surely in this case loads will be visible at once, there will be 
> no occlusion, and if you sweep around with the camera, literally 
> thousands of objects will get paged in/out?

You are right in expecting that different types of scenes might require 
different paging stategies.


BTW I'm no PagedLOD expert, just a user.

> Or am I being a complete noob and interpreting the way PagedLOD works?
> Cheers!
> Andrew
> On Tue, Nov 3, 2009 at 8:36 PM, Angus Lau <angus.lau at safe.com 
> <mailto:angus.lau at safe.com>> wrote:
>     Hi,
>     Thank you for both of your help. It seems that PagedLOD is what I
>     need to use to reduce CPU memory usage. I have tried to use PagedLOD
>     briefly before, but I am not clear how I can make PagedLOD unload
>     the unused child nodes once those child nodes are loaded. It seems
>     that my PagedLOD nodes do not remove the nodes once it creates the
>     child nodes. Could you please give me some explanation about the
>     proper way of using it??
>     Thank you!
>     Cheers,
>     Angus
>     ------------------
>     Read this topic online here:
>     http://forum.openscenegraph.org/viewtopic.php?p=19123#19123
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