What is a gyrotheodolite?
Gyrotheodolite gyrotheodolite is a kind of theodolite with gyroscope device, which is used to measure the true azimuth of a straight line. One of its key devices is the gyroscope, referred to as the gyroscope, also known as the gyroscope. Mainly composed of a high-speed rotating rotor supported on one or two frames. A two degree of freedom gyroscope with a frame; A three degree of freedom gyroscope with two internal and external frames is called a three degree of freedom gyroscope. The installation of a suspended gyroscope on a theodolite determines the north direction of the true meridian using its directional northerness, and then uses the theodolite to measure the horizontal angle between the north direction of the true meridian and the undetermined direction, which is the true azimuth angle. Northing refers to the characteristic of a suspended object that, under the influence of gravity and the Earth's rotational velocity, the axis of the gyroscope will precess and gradually move closer to the true plane, ultimately achieving angular harmonic motion with the true plane as the center of symmetry. The commonly used methods for determining the north direction of the true meridian include the mid sky method and the reversal point method.
What are the precision orientation methods of gyrotheodolite?
At present, the following three methods are often used for precision orientation of gyrotheodolite
（1） Tracking reversal point method (2) Zhongtian method (3) Gyro stationary position method
Here is an introduction to the commonly used tracking reversal point method in our country. When the gyrotheodolite uses the tracking reversal point method to orient on a measuring point, the operating procedure is roughly as follows:
（1） Strictly adjust the theodolite, mount a gyroscope, measure the direction of the measuring line in one measurement loop, and then roughly align the instrument towards the north;
（2） Lower the sensitive part for pre measurement zero position observation;
（3） Perform rough orientation, which can be completed by the attachment rough orientation compass, or by using the two point reversal point method, quarter cycle method, and swing method.
（4） Rotate the theodolite to the coarse directional position, start the gyroscope, and slowly lower the sensitive part of the gyroscope after reaching the rated speed, limit the amplitude, and track it with a micro screw. Tracking should be smooth and continuous. Avoid not tracking in a timely manner, sometimes falling behind the swing of the sensitive part, and sometimes quickly catching up or surpassing a lot. All of these situations affect the accuracy of the results. When the swing reaches the reversal point, continuously read 5 reversal point readings U1U2U3U4U5
（5） Lock the gyroscope and brake it to observe the zero position after measurement;
（6） Measure the direction value of the survey line using one survey set, and when the difference between the two survey sets meets the limit, take the average value as the direction value of the survey line. The calculation steps for the directional edge coordinate direction angle are as follows: gyroscope azimuth=line direction value - gyroscope north direction value geographic azimuth=gyroscope azimuth+instrument constant coordinate azimuth=geographic azimuth - meridian convergence angle instrument constant can be measured on a known azimuth wire or triangular point, and the instrument constant can be used to measure geographic azimuth angle by calculating the following equation, Usually, instrument constants are not used for measuring gyroscope azimuth and control traverse in coal mine metal mines
Main Applications of gyrotheodolite
(1) Tunnel centerline measurement
In excavation projects such as tunnels, the measurement of the centerline inside the pit is generally carried out using long-distance wires that are difficult to ensure accuracy, especially in the case of shield tunneling. Starting from the short reference centerline of the vertical pit, it is necessary to have high angle measurement accuracy and station relocation accuracy. During the measurement, corresponding checks on the ground and underground should also be carried out frequently to ensure the accuracy of the measurement. Especially in densely populated urban areas, the inspection conditions are difficult and it is impossible to carry out excessive testing operations. If you use gyrotheodolite, you can get an absolute high-precision azimuth reference, and you can reduce the costly detection work (the minimum number of check points). It is a highly efficient centerline measurement method.
(2) Directional Angle Acquisition in Intervisibility Disorders
When there is an intervisibility obstacle and the bearing angle cannot be obtained from the known point, astronomical measurement or gyrotheodolite measurement can be used to obtain the bearing angle. Compared with astronomical measurement, the method of gyrotheodolite measurement has many advantages: less dependence on weather, no need for complicated astronomical calculation, and it is easy to calculate closure error because the direction angle of any survey line can be obtained on site.
(3) True North determination required for solar shadow calculation
The height limit for high-rise buildings in urban or suburban areas with sunlight or shadow conditions. When applying for a building, a shadow map should be attached. This solar shadow map refers to the high-precision measurement of the true north direction based on the true solar time of the winter solstice from 8:00 to 16:00 for calculation and surface drawing purposes. At this time, the gyrotheodolite can be used to measure without the influence of weather, time, etc.