CG grass. Any possible ways to do it?
 

Not sure if this is really the best place for this thread. Move it elsewhere if it isn't.

I have always wanted to do an animation with realistic grass in it, but I don't know what the best approach to making and animating it is. I tried, just like everyone else has at one point, to make a bunch of individual strands of grass and use that as grass. Obviously, this does not work because of the amount of memory it uses on your computer and because it is time consuming. I tried making lots and lots of paint FX grass on multiple curves, but that takes entirely too long to render out and doesn't seem to have the kind of effect I'm looking for anyway.

Can you do grass with particles maybe? How do they do grass effects in CG movies? I know in Star Wars all of it was real footage and they composited the CG characters and objects in later, but surely there is a way to do it all in CG. right?

Fur or nurb patches with softbodies might be able to do it faster when it comes to rendering

yeah, I believe fur plugins are being used primarily these days.

ok, I took a nurbs plane with about 15 spans on the U an V and chose Fur>AttachFurDesciption>New. This applied fur to my plane. Now, in the attributes editor for the fur, I changed the length to about what grass should be on my plane. I rendered it out, but the grass isn't thick enough. It's like a few grass pieces scattered over the plane. The only way I can see to change the amopunt of grass that is on the nurbs plane is to adust the U and V samples for the fur. This, however, only changes the amount of grass you see in Maya. It does not change the grass when you render it out. So...like... what's the use of changing the U and V samples for fur??

Mian problem right now is getting the grass to be thick enough. How can I do this?

You might consider checking out David Stripinis's book "The MEL Companion". He has a section in there where he talks about developing a grass generator. The melscript uses poly cylinders for the grass, so you can control the level of detail that you need. It also allows you to specify density, number, height, etc of the grass field. Not sure off the top of my head if it's setup to animate, but I don't imagine that would too difficult to add in.

Thanks, but I'm not really up to purchasing a book right now. I really need something that is easily animated anyway and lots of cylinders seems like it would slow my machine down a lot.

any fur gurus out there who can answer my previous question?

Dark, the samples for U and V is just for a display rep.. you need to change the total count on the fur.. I will look it up if needed.. the exact place..

BTW the fur will render just as long if not a little longer in time, as PFX for the same thing. becouse fur is alot like a specal brush for PFX... and there the same qualtiy as fare as looks.. really PFX is probly a better bet for grass. becouse of the simplisity of what your doing.. as far as render time.. if your furing a animal though fur is the better of the 2..

This is all rather dependant on what you want also.. are you looking for cartoony grass ?? grass that responds to difrent things.. air files.. etc.. realisitc lookign grass ??

What I do, personaly, is determine how close my camera is going to be to a surface, (to determine grass PFX brush detail),
then I'll paint some grass in an area to verify that it looks ok.

Then what I do is save that brush as a preset.
Open a new scene.
Create a nurbs plane.
Cover it with my grass, and match/import my lighting from my target shot.

Create a 2 node or Orthographic-switched camera, and place it at the recorded height off the ground plane for a render.

Then I'll render the plane out at 2k or 3k depending on how much area of undisturbed grass I require for my shot.

Then I just use that as a simple 2d texture in my actual shot.

Looks convincing enough for my needs, and the render-time is quite fast.

Play around with the shader that contains your big 2d grass-map, like:
-add a SLIGHT bump for added detail during those moving motion-blurred shots.
-use a Blinn, or Phong instead of a lambert, or surface shader for that added "glint" from your bump for that "morning-dew" wet look.

Keep in mind, that if you want flowing, blowing, and bending blades of grass, fur and or PFX in 3d is the way to go.

But for medium-high-level flyovers, and fast renders, my technique has worked for me in a pinch:)

Good luck!

Rage: I will be doing close-up animation, so it will need to move just like real grass. I have tried Paint FX grass. but there just never is enough of it no matter what I do. I need a huge field of grass you see...

With paint FX, the grass exists on curves. I tried making lots of straight lines then applying the grass brush to each of them, but the grass still didn't look thick enough. I tried several other things, but they slow down my machine way too much. With fur, it's much easier to manipulate because it's one single attribute, not a million curves with grass applied to each one. It's just way too much trouble. Believe me.

Your idea about applying a grass texture for far away shots with a bump map does seem interesting and useful. I have never thought about doing it that way and will probably try it out here soon.

Pony: Yes, I figured out that the U and V samples only adjust the display. I don't know why this feature exists, but oh well. What I need is the actual thinkness of the fur to be increased. I have gone through pretty much all the attributes and can't seem to find it. Would you mind telling me what it is like you said you could please?

sure thing Darkware. What I did was aply the new fur discription. I didn't change anynames but it should all be in the same place anyway.. select the fur its self. In the attribute editer the midel tab normaly comes up first.. the furFeedBackShape. that has your samples per U and V. you want the tab next to that on the right.. FurDiscription1 is what I have but I didn't change the name this time. It will have a choise box for the light model. thin right under that is the density. Its set to 1000 buy defalt, a gess for your grass, say even a small back yard would be around 100,000.

I would start off with lower figers and see how it gose.. but just so you know I'v had it up to 600,000 but it was like a 10 minuet render.. just for the fur part..

Let me know how it works for you. I would like to hear good things about fur. Let me know my feelings about it are off. I think with grass and it not being fur on a animal that you will find the look of it ok. wandering if fur would show up in a depth map.

ahhhhh. NO WONDER!!! lol I only took it up to 3000. I thought for sure that would be enough to change it noticably. (I mean it's three times the original value, right :P)

ok, so that's what I need to change then. Thanks a lot Pony!