Oriented Principle of Gyro-theodolite

Gyro theodolite is an instrument used to measure true north azimuth by combining gyroscope and theodolite through connecting mechanism. It uses the physical characteristics of the gyroscope itself (fixed axis and precession), the sensitive part of the gyroscope with the center of gravity moved down is used to sensitive the horizontal component of the earth's rotation angular velocity, and under the action of gravity, a northward precession moment is generated, so that the gyroscope spindle swings around the Earth's meridian plane, so as to determine the true north azimuth.

Orientation principle

The gyroscope rotating around its symmetry axis at high speed has two important characteristics: first, it is fixed axis, that is, without the action of external torque, the direction of the gyroscope axis always points to the initial constant direction; Second, it is precession, that is, under the action of the external torque, the gyroscope axis produces precession, and moves close to the vertical plane where the rotation axis of the external torque is located along the shortest path until the two axes are in the same vertical plane.

The true meridian is the intersection between the plane (the meridional plane) of the Earth's rotation axis and the surface of the earth. Therefore, the true meridian of the ground (true north direction) is in the same vertical plane as the axis of rotation of the Earth. When the gyroscope's gyro rotates at a high speed and its axis of rotation is not in the vertical plane of the ground's true meridian, the gyro's axis of rotation will be precessed by the moment of rotation of the earth, and it will be close to the vertical plane where the true meridian and the Earth's rotation axis are located. So the gyroscope The axis of rotation can automatically indicate true north direction.

Under the action of inertia, the axis of the free gyroscope rotating at high speed does not rest in the true north direction, but swings left and right in the true north direction. The maximum amplitude of the east-west oscillation of the gyro axis is called the reversal point. Therefore, the gyroscope is combined with the theodolite, and the theodolite is used to track the east-west reversal point of the cursor, read the level dial and take its average value, so as to obtain the true north direction.

The use of gyro theodolite is related to its structural characteristics. Generally, manual measurement method is used for overhead instruments, and automatic measurement method is used for underhung instruments. Automatic measuring instrument mainly adopts automatic tracking method, multi-point photoelectric timing method and photoelectric integration method. Among them, photoelectric integration method is the most advanced. The manual measurement method mainly adopts tracking reversal point method, transit time method, timing swing method and multi-point timing method.

Application Fields

(1) Tunnel center line measurement

In tunnels and other excavation projects, the measurement of the center line in the pit generally adopts a long distance wire which is difficult to guarantee the accuracy, especially in the case of shield excavation. Starting from the short reference center line of the pit, there must be a high accuracy of Angle measurement and station shifting. In the measurement, the corresponding inspection of the ground and underground should be often carried out to ensure the measurement accuracy. Especially in dense urban areas, inspection conditions are difficult and it is impossible to carry out excessive inspection operations. If the gyrotheodolite can be used to obtain an absolutely high-precision azimuth reference, and can reduce costly detection operations (minimum checkpoints), it is a highly efficient centerline measurement method

(2) To obtain the direction Angle when viewing obstacles

When the direction Angle cannot be obtained from a known point due to the obstruction of visibility, the direction Angle can be obtained by astronomical measurement or gyro theodolite measurement. Compared with astronomical measurement, the method of gyro theodolite measurement has many advantages, such as less dependence on weather, no complicated astronomical calculation, and easy calculation of closure error because the direction Angle of any measurement line can be obtained in the field.

(3) True north determination required for shadow calculation

In urban or suburban areas, there are height restrictions for tall buildings under sunlight or shadow conditions. The sun shadow should be attached to the building application. This solar shadow map is based on the true solar time of the winter solstice from 8:00 to 16:00, for the purpose of calculation and map drawing, the true north direction is determined with high accuracy. At this time, the use of gyro theodolite measurement is not affected by weather, time, etc.

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