I am trying to move relative to a plane feature. I have reviewed the content already at these links:
however I don’t think it gives me the complete answer. To summarise I wish to:
 Find the position relative to a plane feature. As already discussed this can be done with:
p_2=pose_trans(pose_inv(p_1),Plane_1)
where p_1 is the position in the base coordinate system.
Plane_1 is the plane feature that I wish to reference.
p_2 is the point relative to Plane_1.

I then wish to add offsets relative to the position in Plane_1.
e.g.
p_2_offset = p_2
p_2_offset[0] = p_2_offset[0] + x_offset
p_2_offset[1] = p_2_offset[1] + y_offset 
Now the main problem is how do I now translate this offset position back to the base coordinate system. Logically I thought I should try the following:
p_3 = pose_trans(pose_inv(p_2_offset),pose_inv(Plane_1))
where pose_inv(Plane_1) gives the position of the base coordinate system relative to Plane_1 coordinate system. I have tested the code and it doesn’t give the correct result. Does anyone have any ideas?