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    See operating CAD ..

    Joints:
    Joints are objects of submodels becoming exported into the parent model.
    Joints using the code letter J.

    Applications for Joints:

      Assemblies, Schematics (electrical, hydraulic, pneumatic)
           Importing points as connecting points (example)
           Import a reference-system (plane) for positioning a submodel.

      Kinematics
        NOT YET IMPLEMENTED.

      Animation paths, Camera Drives
        NOT YET IMPLEMENTED.

    Joints on points:

      The corresponding object (point or plane)  is created automatically
        when inserting this model as external submodel -
        the object is imported in the parent model.
      Example:
        The current model is an electrical resistance;
        the connection points are defined as joints.
        When inserting the resistance as a submodel the
        Connection points automatically generate normal points.
        See sample_DiagEl1.gcad model.

    # Export:
    J1 = P20    # export point in subModel

    # Import: (is created automatically by import of external submodel as M20)
    P20=IMP M20 J1   # import Joint Nr.1  from subModel M20

    Example:
    - create model with points to connect (eg my_jnt1.gcad):
      - create a rectangle, create the connection-points
      - set the connention-points as JOINTS:
        CAD create joint-export, sel point ..
      - store model as eg my_jnt1.gcad

    - create model using external connection-points (eg my_jnt2.gcad):
      - load model with connection-points (eg my_jnt1.gcad)
        CAD Submodel "M external Model" my_jnt1.gcad, set position, OK.
        The connection-points have been created automatically - see MAN
      - the connection-points can be used as normal points ..
      - store model as eg my_jnt2.gcad

    See also model Data/sample_DiagEl1.gcad

    CAD-Functions Joints:

    Joint-export
     Export the selected object of the current model as a joint.

       joint-object       select point or plane

    Output:
    J1 = P20