grass placement question

[freedomfries]

Hi Forum!

I'm a newb to terragen and hoping you could help with a placement issue with a grass clump population. I'm using 2.5 on Windows 7 64 bit. If you look at the gif of my first scene, the grass population seems to grow over the terrain, and up the trunks of trees, without really following the terrain. The pic has renders with grass enabled and without, so you can see my terrain underneath. I simply want the grass to follow this terrain, including the little mounds.

My grass population is connected to the compute terrain node, so I'm not sure what is going on here. It's a short grass, with scale variation of clumps from .5 to 1.5.. Other than that, I haven't changed variables. And yes, I made sure that "sit on terrain" is ON. Any suggestions are greatly appreciated.

[N810]

It kinda looks like the grass is displaced some how,
is it connected to the base terrain or some displaced surface ?

[freedomfries]

It kinda looks like the grass is displaced some how,
is it connected to the base terrain or some displaced surface ?

The population is connected to the compute terrain node. As it should, right? But yeah it does look like it's hovering over the terrain, in fact, there's no shadow from the grass visible. Clearly it looks above it, but I see no reason why. There's no extra transform... Shouldn't it follow the terrain?

[choronr]

Did you use a distribution shader for the grass setting maximum height and/or slope?

[freedomfries]

Did you use a distribution shader for the grass setting maximum height and/or slope?

No I didn't. I'm attaching another screen cap of my population and node tree... Pretty standard stuff I would assume.

[Tangled-Universe]

Do you displace the terrain below the compute terrain?
I see a node called "rocky texture" which is a powerfractal by the looks of it.

You may try connecting the very last shader of your network, the one which output goes into the planet node, into the populator "terrain shader" input port as "sit on terrain" shader.

The "sit on terrain" shader (2nd tab in populator node) is the shader the software uses to calculate the surface the population needs to be put on.
Now you use the surface calculated by the compute terrain, but if you displace below that compute terrain then there's a chance that the populations don't align with the terrain anymore.
Displacing "a little" (yes, arbitrary) is ok, but if it's too much then you may run into issues.

So if you displace much then you may need to use the last shader of the network to have the populations sit on.
If even that doesn't work then it's even possible you may need to add a compute terrain after your very last shader.
HOWEVER, you don't need to connect it to the planet per se.
That's the versatility of these nodes, you can decide which part uses what kind of "state of information".

[freedomfries]

You are correct, I am using a couple power fractals. Those are used for the distribution of color only (snow caps, green valley) of my surface layers. I made sure to turn off the displacement of the nodes in this part of my tree (the shaders). Nevertheless, I tried what you suggested, first connecting my grass population to the last shader, then mapping a new compute terrain after said shader and using it in the "sit on terrain" field. Neither worked.

[paq]

Hi freedomfries,

First please forgive my english

It's pretty hard to say if the grass are following the terrain (or not). I would suggest to first using a pretty small and constant scale (no scale variation) to have a better overview of what's going on.
Maybe the grass clump size hitself is pretty big ?  The default value of the clump diameter is 10 m, did you change it ? because even if your populator spacing is very low, there are lots of overlapping grass that follow the 'flat' terrain.

What is the 'average' size of the little mound ? (there is a mesure tool above the render preview windows). If a mound is about 1 m, clump patch size should be smaller ... (you can access to the clump node by double click on the little cross of the pop grass node).

[Klas]

Try a smaller value of gradient patch size on "Compte terrain".

[Tangled-Universe]

Try a smaller value of gradient patch size on "Compute terrain".

Yes that would be my next suggestion too, although the default 20m can deal with almost anything in many cases, but you never know.

The other suggestion of making a small population in front of your camera to see what's really going on is something you should definitely do too.

[freedomfries]

Thank you all for the helpful hints. Changing clump size, terrain  compute settings and clump placement did help. It's still not perfect as you see.

1) Can I get my grass to grow properly over my little mounds? Otherwise I guess I can place individual objects there... Perhaps I have hit the limit? I will try an even finer grid on compute terrain.

2) The grass is on very high quality, and still renders like noise. I see no shadows in it. Is this the best the grass object can do? IF yes, I'll have to use some imported geometry because frankly it doesn't look realistic. Check out my render settings. I turned them up pretty high.

Thanks again!

[Oshyan]

The built-in grass object is intended largely for background and fill-in. If you're looking for high-quality, realistic grass in the mid-to-foreground, you should definitely use an imported object. Also, the built-in grass object is a flat plane of grass blades, so depending on the size you set for that plane, it may stick out since the grass plane does not conform to the terrain (the base of the grass plane instance may be sitting on the terrain but the plane still can extend away from the terrain and appear to be floating). To avoid this you can use smaller grass patch sizes.

- Oshyan

[freedomfries]

Thanks Oshyan, this was really helpful... As for the shadow casting, I suppose it's not casting shadows, just adding extra color on top of your ground plane?

I'll move on trying to make this hero grass...

[Matt]

I noticed that you have turned off "Ray trace objects" on the render node. You'll get best results by turning that on.

The grass clumps should cast shadows. It's possible that rendering without ray trace objects could affect small-scale shadows. I'm not sure if that's the problem here, but try turning that on anyway.

The grass clumps could be made to flow over the terrain a little better if you activate "lean to normal" on the populator, but you will still run into some problems because the grass clump radius is quite large. A small radius can help with that, but ultimately you may want to replace with more realistic grass models.

Matt

[paq]

Well this default grass object is not bad at all, I use it all the time Maybe an option to get a little bend on the strip would be welcome.