The gyro that rotates at high speed around its axis of symmetry has two important characteristics: one is the fixed axis, that is, the direction of the gyro shaft always points to the initial constant direction without external torque; the second is precession Sexuality, that is, under the action of external torque, the gyro shaft is precessed, and the vertical plane of the rotation axis of the shortest path is close to the vertical plane until the two axes are on the same vertical plane.
The true meridian is the intersection of the plane (meridian plane) of the Earth's rotation axis with the Earth's surface, so the ground true meridian (true north direction) is in the same vertical plane as the Earth's rotation axis. When the gyro of the gyroscope rotates at a high speed and its rotation axis is not in the vertical plane of the true meridian of the ground, the gyro rotation axis is precessed by the moment of the earth's rotation, and the true meridian is close to the vertical plane where the earth's rotation axis is located, so the gyro The axis of rotation can automatically indicate the true north direction.
The rotating shaft of the high-speed rotating free-gyro does not stand in the true north direction under the action of inertia, but oscillates in the true north direction. The maximum amplitude of the gyro's rotating shaft is called the reversal point. Therefore, the gyroscope is combined with the theodolite to track the reversal point of the cursor with the theodolite, read the horizontal dial reading and take the average value to obtain the true north direction.
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