If the GPS can be oriented in line with the vehicle's axis and a magnetometer/compass (is there a vehicle?) then heading bearings can be used to calibrate the declination. Assuming the compass has compensation for nearby iron masses...
If the GPS can be oriented in line with the vehicle's axis and a magnetometer/compass (is there a vehicle?) then heading bearings can be used to calibrate the declination. Assuming the compass has compensation for nearby iron masses...