If I make particle grass (e.g: http://blenderartists.org/forum/showthread.php?t=68269 ) the grass grows out sideways from the hills. Adding z gravity makes the ends droop, but the grass is still growing out at strange angles, especially on steep hills. Real life trees and grass grow up from the ground vertically regardless of the slope. What settings will achieve this with particle grass?
I’m not sure what your settings are, but maybe look at the particle velocity settings - normal force will cause the grass to grow out of the normals of the mesh, and random will cause random directions- my guess is you have too high of one or the other of these and not enough constant force going up (probably a positive Z is what you want, with very little contributions from the others)
you can try using a curve guide or a deflector too- curve guides give you a nice way of visually controlling how the blades will look.
I just tried to produced something realistical on uneven ground (i just used a half sphere sqashed in the Z axis)
My settings …
Particles
Emit
- Amount: 1000
From - Rand [X]
- Even [X]
Particle Motion
Velocity
- Normal: 0.002
- Random: 0.005
Force - Z: 0.05
Strands (Material settings)
- Start: ~2.0
- End: ~1.0
This produces grass that grows out normal to the ground on its root, but then goes straight into the sky.
These are just testing values, some tweaking is still needed of course 
Werner
Thanks for your work.
Your settings are very similar to ones I got after a bit more playing around. I got…
PARTICLE MOTION
Normal: 0.001
Object: 0.000
Random: 0.002
Texture: 0.000
Damping: 0.500
…with Z-force 0.03 and the Amount set to 30,000
The grass is not for anything serious although I’d like to get it better for my own learning. I’m teaching blender in class and am about to introduce some to bump maps. An idea I had was for students to create their own “Maori Carving” design in some other package (e.g: Inkscape) and then port that as a bump map onto a wooden slap to attempt to make a crude carving.
I figured I would start off with a base design showing hills and the slab, ready for them to add their map (these are young kids, and for them making their own hills will come soon enough but later)
At the moment, my base slab with my own carving bumpmap design looks like this…
As you can see in the foreground, the grass leaves the ground at a slight angle and then straightens up due to the z-force gravity. This is not ideal as the curve should be in reverse: blades should come out of the ground straight, and then curve over if they need to.
Curve guide sounds like something I should read up on. Would that allow me to make long hair that flows over someone’s shoulders without going through them?