Electronic animal containment system with direction of approach determination

An electronic animal containment system with direction-of-approach determination, or direction-sensitive animal containment system. The direction-sensitive animal containment system generally contains a transmitter unit connected to a wire loop bounding a containment area and a receiver unit carried by the animal. The direction-sensitive animal containment system of the present invention generates a containment field having polarity and retains the polarity information when the containment field is sensed using a sensing coil optimized along the azimuth. The receiver unit also generates a gravity vector to determine the orientation of the receiver unit. The gravity vector is combined with the containment field vector to produce a function that automatically yields a sensing coil output that is independent of the orientation of the receiver unit. The polarity of the sensing coil output allows determination of the direction from which the receiver unit is approaching the wire loop.