A Primary Joint (PJOI) is owned by a Primary Node. Its position is derived from that of its owning Node.

A Secondary Joint (SJOI) is owned by a Secondary Node. Its position is derived from that of its owning Node, and thus, in turn, from the position of the Section which owns that Node.

A Compound Joint (PCOJ or SCOJ) is positioned relative to a Node, as for a PJOI or an SJOI, but all settings which define its connections are associated with subsidiary SubJoints owned by the Compound Joint (one SubJoint for each connection).

The user will most often create and position Joints automatically using the STRING command (refer to Creating and Connecting Sections Automatically). This section describes how the user can carry out these operations independently and how to modify the positions of Joints which have been created previously.