A corner reflector [CR] = 3 mirrors,90 deg. between any two (like a corner of a box ). It reflects
the beam parallel to the incident one.
You can measure the angle between any two CRs (2 CRs may be very close so their angle is minimum). If you know the position of the CRs and the angles, you can calculate your position.
If you rotate the beam, you can measure the angles very accuretelly. ( Tachom., PLL etc.)
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