How can I make a number of objects sit "snugly" on an irregular surface?

Question

How can I make a number of objects (or copies of one object) sit "snugly" on an irregular surface - like trees or rocks on irregular ground?

I once came across a tutorial that covered this but I cannot find it again.

The only thing I can think of is to create a "pseudo object" whose vertices represent the desired relative target locations then use retopologize to make the "pseudo object" vertices conform to the surface of the irregular target object and, finally, use dupliverts to place the added objects.

Answer 1

This might not be as 'snug' as you might want but for the use case you described above, it is perfect. You can do this with a particle system and groups.

Group all your objects that you want to sit on the ground and add a new Particle system to the ground.

Change the type to Hair and under Render change the type to Group and select the group you had previously created, your objects will be scattered randomly across the ground.
(Note: This might lag your scene as the default Emission amount is 1000, so change it before or after).

I imagine this can be ideal for scattering rocks and or brush over some terrain. I won't go too indepth on the other settings as they are pretty intuitive and you will more likely get your desired results if you experiment. ^{(larger image here)}

Answer 2

• For trees, you should model enough roots past the origin that go into the ground for worst case scenarios.
• For rocks, you can use Rigid Body Physics and let the simulation settle them on the ground.
• For other types of objects that need to be deformed to sit on a surface, you can use the Shrinkwrap object modifier.

Answer 3

The easiest way I know is creating a particle system on the terrain or ground object.

First thing to do is to make in a hidden layer a series of related but different objects (three, four, ten rocks or trees). Then you select them all and group them (with CTRL + G).

Then you create the particle system in the terrain object, chosing the number and pattern of distribution of the objects (jittered and random should be ok to the rock or tree scenario). The start and end frames of the particle system should be one, and the life of the particles should match de length of your animation.

Choose "no physics" (instead of the default: Newtonian). Then the particles would be scattered and won't move their place.

In the render settings (inside particle settings), choose "group", and select your newly created group.

If your computer becomes too slow, you can chose in the display section to display a point or the bounding box of the particles.

There are some settings that may help to match the rotation of the particles with the one you want: the easiest is, in the render settings where you chose "group", to check the "rotation" option. The second one is to check and adjust the "rotation" group of settings, specially the "phase" one. A third option is to go back to "newtonian", then in velocity section set the normal to 0, and go back to "no physics". The last one is to change the rotation of the objects in edit mode.

Happy blending!

Answer 4

Drop to Ground (Addon)

http://wiki.blender.org/index.php/Extensions:2.6/Py/Scripts/Object/Drop_to_ground

lets you select objects and a ground plane and how to orient the objects once they reach the ground plane. The addon comes with simple controls and good user guide.