Grass rendering problem

[cloeon]

I've got a scene with a building and some trees. I've just added a grass field doing it the same way as in the realgrass tutorial. When I render the scene most of the time all objects are not rendered and some times a few of the tress are rendered. When i delete the grass field object all the other objects in the scene appears in the render. Obviously theres something wrong with the way i make the grass field but i dont get why mentalrey seems selective in which objects it can render. I'm really careful to render the correct view. I've used Forest to scatter the trees in the scene and it works fine. Can it be the amount of polygons in the grass field that bring mentalray to its knees?

[iToo]

Unfortunately Mental Ray is much more limited in the number of render instances that it can handle, compared with VRay. For our tests, the limit would be around 500.000 items. Above this value, the render times grows exponentially and (depending of the Max version), it would be unstable:

http://www.itoosoft.com/forestpack/reference/rendering.php

Anyway, with 500.000 items you can create huge extensions of grass, and Mental Ray has been greatly improved in the latest Max releases. So, the problem would be other. In any case, you can see the number of estimated render items at General->Forest Stats.

What version of Max and Forest do you use ? If possible, please send us a test scene so we can reproduce the problem here.