From BlenderWiki

Floor Constraint

Description

The Floor constraint allows you to use its target position (and optionally rotation) to specify a plane with a “forbidden side”, where the owner cannot go. This plane can have any orientation you like. In other words, it creates a floor (or a ceiling, or a wall…)!

Options

Targets

This constraint uses one target, and is not functional (red state) when it has none.

(Bone Target)

When using a bone target, you can chose where along this bone lays the target point, using the Head/Tail numeric field.

Sticky

This button makes the owner immovable when touching the “floor” plane (it cannot slide around on the surface of the plane any more). This is fantastic for making walk and run animations!

UseRot

This button forces the constraint to take the target’s rotation into account. This allows you to have a “floor” plane of any orientation you like, not just the global XY, XZ and YZ ones…

Offset

This numeric fields allows you to offset the “floor” plane from the target’s center, of the given number of Blender Units. Use it e.g. to account for the distance from a foot bone to the surface of the foot’s mesh.

Max/Min

This set of (mutually exclusive) buttons controls which plane will be the “floor”. The buttons’ names correspond indeed to the normal to this plane (e.g. enabling Z means “XY plane”, etc.)

By default, these normals are aligned with the global axes. However, if you enable UseRot (see above), they will be aligned with the local target’s axes.

As the constraints does not only define an uncrossable plane, but also a side of it which is forbidden to the owner, you can chose which side by enabling either the positive or negative normal axis…

E.g, by default (Z), the owner is stuck in the positive Z coordinates…

Example

Floor constraint example.

No constraint.	Floor just added.
Target rotated without UseRot.	Floor plane offset.
Target rotated, with UseRot.	UseRot and Offset.

In the (Floor constraint example) pictures, the yellow line materializes the “floor” plane.

• In (Floor just added), the Min/Max normal axis is Y, and there is no offset.
• In (Target rotated without UseRot), you can see that by default, rotating the target has no influence on the constraint.
• In (Floor plane offset), the “floor” plane has been offset of -1.5 BU, and hence is now “below” the normal location of Owner empty…
• In (Target rotated, with UseRot) and (UseRot and Offset), you can see that with UseRot enable, the target’s rotation now controls the orientation of the “floor” plane.