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[KelvinNZ]

Hi,
The trees are just billboards, but we will be also switching to models up close. I guess there can be around 200,000 of such trees rendered in an average forest scene, maybe more - maximum density is ~44,000 trees per square km, one tree in one 4.8x4.8m cell. Performance depends on the actual density of the trees on the visible terrain tiles - for the areas that are almost completely covered by trees that that would make 400-500 thousand trees rendered.

Billboards are generated at run time by a geometry shader from a tree coverage map (per terrain tile). The map is computed using local terrain properties like elevation, slope and curvature, combined with fractal noise values to get the fractal-like distribution of trees in nature.

As for the plans - the vegetation will be derived from land type layer with 500m resolution. Each land type defines probabilities of occurrence of distinct vegetation types, which will be generated and mixed using fractals in a way that preserves the probabilities. The attainable variety of vegetation should be sufficient, problem will be to collect data for all the vegetation types for all the land classes we'd like to have.

The challenge does appear to be the availability of all vegetation/tree types. There must be a data set out there somewhere that could fill this void? Surely!

[foxfiles]

There are several of such libraries of 3D plant models Onyxtree, Bionatics, Xfrog, speedtree, etc...
with hundreds of species, at various growth stages for each tree.
They are even sorted per regions (ex: Europe, USA, Japan) and are available with several representation versions for rendering at various levels of details.
 So static material to work with exist and I am pretty sure that our OT's friends know a lot about these libraries.

But they have a price, represent a large amount of data, they are static models and so on...

The most complex thing is also what Cameni's saying above : create the method(s) to "automatically populate" the vegetation on the ground 
it's based on many rules : Earth's biomes, seasons, terrain topo, densities, statistics, probabilities, etceterra  -------- well it's a big subject in itself
 

[Midviki]

The most complex thing is also what Cameni's saying above : create the method(s) to "automatically populate" the vegetation on the ground 
it's based on many rules : Earth's biomes, seasons, terrain topo, densities, statistics, probabilities, etceterra  -------- well it's a big subject in itself

So... without a method...if we would like to hand pick our own personified models of tree's and place them one by one in some zone, we won't be able to use too many of them or something like that?Even if we have lets say 16GB or 32GB of Ram?Can they be all loaded?.. And I'm not talking about UFO speed, I mean normal walking and you would see tree's from the other hill or top of the mountain, will it be?And probably the lighting will work as on buildings since those tree's are objects like buildings I guess, right?

[cameni]

If you place trees individually as objects, they will be treated as objects, limitations on the number of them will apply. It's not a problem of RAM on the CPU, but on the GPU. However, it's the model size what counts, multiple instances of the same tree don't take much space.

With trees it's even more important to have good LOD levels.

[Midviki]

Yep.. especially if you want to cut them down... or crash a 747 plane in the middle of the forest.