The gyroscope in the gyroscope rotates around its axis of symmetry at high speed has two important characteristics: First, it is fixed-axis, that is, the direction of the gyro axis always points to the initial constant direction without the effect of external torque; second, it is precession Sex, that is, under the action of external torque, the gyro axis produces precession, and the vertical axis of the rotation axis of the outward torque along the shortest distance is close until the two axes are on the same vertical plane.
The true meridian is the intersection of the plane (meridian plane) that passes through the earth's rotation axis and the earth's surface, so the ground meridian (true north direction) is in the same vertical plane as the earth's rotation axis. When the gyro's gyro rotates at a high speed, and its axis of rotation is not in the vertical plane of the true meridian, the gyro axis produces precession under the action of the earth's rotation torque, and approaches the vertical plane where the true meridian and the earth's rotation axis are located, so the gyro The axis of the can automatically indicate the true north direction.
The rotation axis of the free-spinning gyro does not stand still in the true north direction under the action of inertia, but swings left and right in the true north direction. The maximum amplitude of the east-west swing of the gyro axis is called the reversal point. Therefore, the gyroscope and theodolite are combined, the theodolite is used to track the reversal point of the cursor, and the reading of the horizontal dial is read and the average value is taken, thereby obtaining the true north direction.
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