Hello! I have some questions on the URDF frame. From the figure in this page (URDF Joint element), I find that the joint's elements , xyz and rpy are relative to the parent frame. Which frame does the parent frame here refer to? Does it refer to the previous joint frame?

Another question: From the figure in this page (URDF Link element), I find that the properties of the link's inertial , xyz and rpy are relative to the link reference frame. Could you please explain which frame does the link reference frame here refer to ? Does it refer to the joint frame in this figure (black)?

Any advice is appreciated.

Thanks!