Carrara F.A.Q (Last Updated: 2021 Sep 21 4:09 pm)
I'm trying to grow some grass on a Carrara terrain, but sadly none of my attempts seem to work.
The first thing I've tried was to apply a hair object to a terrain. I guess Carrara tried to simulate it, but nothing ever showed up - so I figure perhaps a terrain isn't a good surface to grow hair directly. No problem.
My next idea was to insert a plane and grow my grass on that, by applying the hair object to the plane. Very promising!
The next step then, or so I thought, would be to add the hairy grass plane to a surface replicator, and use the terrain to replicate it. To my surprise, only the plane is replicated, sadly without the hair growing on top of it.
I guess using the hair object for growing grass on a terrain isn't the right approach then? How else could I do it?
I've seen Colin Boyd's video on modelling some grass and using that in a surface replicator, which is another interesting approach: Creating realistic Grass in Carrara
I usually use several modelled grass objects inside a single surface replicator - that creates realistic diversity. I have also used modifiers on those objects (like punching or bending modifiers) to create wind effects. (if you do not randomize the orientation of your replicated objects, or randomize it very slightly without radical rotations, they will all bend in the same direction - like realistically windswept grass). If you want to take a look at my gallery, I have used this method in "You've Got Mail", "Personal Space", "It ain't easy being green." and "Odin of OZ" images.
You can replicate objects directly on a terrain object. You can use the shader or a map to control distribution of the objects on the terrain. If you use a shader mixer of black and white colors (or between) in the replicator modeler's menu, then objects will be placed on white but not on black. You can use slope to just place objects on flat surfaces (or just steep), use elevation to either fill or empty valleys, use a wires function to replicate stripes, etc. There is no need to convert the terrain to a vertex object first.
As Antaran said, hair is not really the best way to create grass but you can grow hair directly on a terrain - just make sure you select "Geometry Based." Also keep in mind your scene size - in a Large scene 30cm high grass is going to impossible to see - you would need hundreds of millions of hairs to start to notice the effect. Note that the hair shader is hugely important to create a decent effect - you need variation in color and length, a tiny amount of frizz and wave, some clumping and a little bit of density variation (I didn't use that last one in this example). The hair scale is also important - for this example I used the Very Large thickness and in the shader I set the root to 100% and the tip to 40%.
Below is an example of hair-based grass on a Medium sized terrain. Note that I only added grass in the area right in front of the camera so that I only needed to use 25,000 hairs instead of whatever crazy amount I would need for the whole terrain. If I'd been doing this for a render I would have covered slightly more of the terrain and used a better shader on the more distant terrain so it looked more like the grass continued on. I would have spent more time of the hair shader too - I spent longer editing this post than I did setting up and rendering my example. :)