I need to write a script, which makes sure, that the tip of my armature never gets under the ground, which will be a flat plane. how would i access the global position of the posebones tail?
If you have your armature object as
arm, you can get its nth bone’s tail local position (i.e. its pose location in armature’s object space) with
arm.pose.bones[n].tail, so to get that in world coordinates, just multiply it with the armature’s world matrix:
arm.matrix_world * arm.pose.bones[n].tail.
Note however it may be simpler (in simple cases) to use a bone constraint like
Limit Position ones…