Hi Peter,

thanks for answearing! The procedure is clear, but what if I have two rounded contact surface like in the picture? 

contact pressure

This is exploded view to let you know that I want to know the pressure at the contact surface between the sphere and the box, that is a convex or concave interface. Should I put the coordinate system at the central bottom of the sphere in order to insert a surface that interfaces with the sphere only at one point?