"Christoph Hormann" <chr### [at] gmxde> schrieb im Newsbeitrag 
news:dg0ifb$2oi$1@chho.imagico.de...

> Could you elaborate?  Lots of mesh instances of course take memory (much 
> less than copying the mesh though) but this should scale without problems 
> as long as you have enough memory and the performance should be O(log n) 
> as long as the trees do not overlap too much.


It's only my experience, that with millions of objects my computer gets slow 
even with 2 GB memory.
Beside, with about 11 million copies of anything the coordinates file alone 
takes 1.5 GB memory.
Problems are much more severe with  normal meshes or CSG objects, but it 
depends on the object complexity.
I'll try to make a bit of more exact statements in the next days.


> - Esp. with lower tree density you have the problems that trees with their 
> bottom below visibility (only the top looking above a mountain ridge for 
> example) don't get placed.


That's true, therefore the method is best in densily populated cases, but I 
can think of some workarounds.


> To avoid this but still keep the number of trees placed low you can use 
> the normal scene space placing and trace a 'visibility ray' to the camera 
> location to check if to actually place the tree.  If you trace this ray 
> from the top of the tree this will solve the issue.  The major 
> disadvantage is of course this is very slow (lots of unsuccessful tests, 
> two traces per test)


This works not always. In some cases you can see only parts of an object, 
but not base or top.
Especially at near overhangs you can need perhaps 5 or more traces.
Of course it takes time, therefore I usually decouple coordinates generation 
and scene rendering.


> - it only works for camera types you have written a mapping function for. 
> For this might be good to have scene language support for image 
> space/scene space transformation.


That's the biggest drawback.
Of course its possible to increase the cam_ang value for the camera angle 
during the coordinate generation, if you don't use extreme camera types or 
settings.

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