/* key dimensions

   joint[0] = Entire arm rotates around a vertical axis at its inner end
		which is attached to the earth.  A value of zero means the
		inner arm is pointing along the X axis.
   D1 = Vertical distance from the ground plane to the center of the inner
		arm.
   D2 = Horizontal distance between joint[0] axis and joint[1] axis, ie.
		the length of the inner arm.
   joint[1] = Outer arm rotates around a vertical axis at its inner end
		which is attached to the outer end of the inner arm.  A
		value of zero means the outer arm is parallel to the
		inner arm (and extending outward).
   D3 = Vertical distance from the center of the inner arm to the center
		of the outer arm.  May be positive or negative depending
		on the structure of the robot.
   joint[2] = End effector slides along a vertical axis at the outer end
		of the outer arm.  A value of zero means the end effector
		is at the same height as the center of the outer arm, and
		positive values mean downward movement.
   D4 = Horizontal distance between joint[1] axis and joint[2] axis, ie.
		the length of the outer arm
   joint[3] = End effector rotates around the same vertical axis that it
		slides along.  A value of zero means that the tooltip (if
		offset from the axis) is pointing in the same direction
		as the centerline of the outer arm.
   D5 = Vertical distance from the end effector to the tooltip.  Positive
		means the tooltip is lower than the end effector, and is
		the normal case.
   D6 = Horizontal distance from the centerline of the end effector (and
		the joints 2 and 3 axis) and the tooltip.  Zero means the
		tooltip is on the centerline.  Non-zero values should be
		positive, if negative they introduce a 180 degree offset
		on the value of joint[3].
*/