Problem with populations...

[Cemoa]

Hey all,

Lately I've been trying to include more and more populations (mainly grass) into my renders, but I have been having some problems. For reasons unknown to me, my grass population always seems to render itself underneath my terrain. I know that they are there since I can see the b-boxes in the preview render, and when I render the image the grass is rendered before the terrain (in a darker color, almost like they are being rendered in the shadows) then the terrain is rendered over the grasses. I am only having this problem with populations, when I manually insert objects they sit on the terrain perfectly. My terrain is usually pretty simple, involving power fractals (both large and small displacements) and usually fake stones, although I threw in a crater shader and strata shader in my latest render.

Sorry if I was a bit vague, I really don't have time to go into detail with this at the moment. Is there anything you guys can think of that would be causing this problem?

[RArcher]

First thing, I would try changing the "Sit on Terrain" function in your population to be the last node before the planet shader.  It is by default set to your compute terrain node, but if you add many surface layers and/or displacement after that you can find that the computed terrain is below the actual terrain.

[Cemoa]

I just tried hooking up the population to my last surface layer instead of the compute terrain and it seemed to fix the problem of the grass sitting underneath the ground. Instead, though, I now have grass that seems to be floating above the terrain almost as if it is on an invisible plane that is tilted diagonally. I'll try and tweak it tomorrow to see if I can get it to sit flush on the ground. Thanks for the quick response!

[Henry Blewer]

In the population window, go to Seed. Hit the Random button. It should recalculate the population so it sits properly. If that does not work, make sure there are not any offsets, especially vertical offsets effecting the population. This can be caused by power fractals, but I have only encountered this once, long ago in an early beta release.

[Feenixnz]

I have the same exact problem with a scene I've been playing around with. I do have negative offset values in my network. I could turn these into positives but it will change the look of my terrain. I havent gone back to though as Im currently working on a project but would love to see this one resolved!

is this whats happening?

http://forums.planetside.co.uk/index.php?action=dlattach;topic=7434.0;attach=19161

[Henry Blewer]

I think I remember that. The problem there was where the objects were being placed. I think object placement is calculated along the x and z planes. The y (vertical) is the height of the terrain. The objects were populated along a nearly vertical cliff. This does not work well.
I wish I had a better technical knowledge of how Terragen 2 works. I would guess that the populater averages between data locations. The area in between is interpolated between these points for displacement. It may not be possible to fix this without suing functions to determine 'where' to place the objects. I am barely familiar with the use of the function set.