Gyro Theodolite Application

Principle of gyrotheodolite
Gyroscopic theodolite, is a gyroscope and theodolite through the connecting mechanism for the determination of true north azimuth of the instrument.The gyroscope rotating around its symmetry axis at high speed has two important characteristics: first, it is fixed axis,without the action of external torque, the direction of the gyroscope axis always points to the initial constant direction; Second, it is precession, 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 of the Earth's axis of rotation (the meridian plane) and the Earth's surface, so that the true meridian of the ground (true north direction) is in the same plumb plane as the Earth's axis of rotation. When the gyroscope gyro rotates at a high speed and its axis is not in the plumb plane of the true meridian on the ground, the gyroscope axis generates precession under the action of the earth's rotation torque and is close to the plumb plane where the true meridian and the earth's rotation axis are located, so the gyroscope axis can automatically indicate the 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.

Application of gyrotheodolite
Gyroscope instrument was originally used for navigation, but with the development of science and technology, it has also been widely used in aviation and aerospace industry. Gyro instrument can not only be used as an indicator, more importantly, it can be used as a sensitive element in the automatic control system, which can be used as a signal sensor. According to the needs, gyroscopic instruments can provide accurate signals such as orientation, level, position, speed and acceleration, so that the driver or the automatic navigator can control the aircraft, ship or space shuttle and other navigational bodies to fly according to a certain route, and in the guidance of missiles, satellite vehicles or space exploration rockets and other navigational bodies. These signals are directly used to complete the attitude control and orbit control of the vehicle. As a stabilizer, gyroscopic instruments can make the train travel on the monorail, can reduce the sway of the ship in the wind and waves, can make the camera mounted on the aircraft or satellite relative to the ground stability. As a precision test instrument, gyro instruments can provide accurate orientation reference for surface facilities, mine tunnels, underground railways, oil drilling and missile silos.

(1) Tunnel center line measurement

In excavation projects such as tunnels, the centerline measurement in the pit generally uses long-distance conductors that are difficult to guarantee accuracy, especially for shield excavation. From the short reference centerline of the pit, it must have high angular accuracy and shifting. Accuracy, the ground and underground corresponding inspections are often performed during the measurement to ensure the accuracy of the measurement. Especially in dense urban areas, the inspection conditions are difficult and it is impossible to carry out excessive inspection operations. If the gyro theodolite is used, an absolutely accurate azimuth reference can be obtained, and the high-cost inspection operation (minimum checkpoint) can be reduced, which is an efficient centerline measurement method.

(2) Obtaining the direction angle when the obstacle is seen

When there is a visual obstacle and the direction angle cannot be obtained from a known point, the azimuth measurement or the gyro theodolite measurement method can be used to obtain the direction angle. Compared with astronomical measurements, the gyro-theodolite measurement method has many advantages: it has less dependence on the weather, no complicated astronomical calculation, and the direction angle of any line can be obtained in the field, and the closure difference can be easily calculated.

(3) True North determination required for day shadow calculation

There are height restrictions on high-rise buildings in the city or suburbs that have sunshine or daylight conditions. When applying for a building, a daily photo will be attached. This day's image is based on the 8:00 to 16:00 of the true sun of the winter solstice. For the purpose of calculation and drawing, the high-precision true north direction is measured. At this time, the measurement using the gyro theodolite can be affected by weather, time, and the like.

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