How to carry out GPS fast static measurement? Take an instrument as an example.

1. Classic static positioning mode

(1) Operation mode: two (or more) receiving devices are installed at the two endpoints of one or more baselines respectively, and more than four satellites are observed synchronously, and each time period lasts for 45 minutes to more than 2 hours. The work arrangement is shown in Figure 8- 10.

(2) Accuracy: The relative positioning accuracy of the baseline can reach 5 mm+ 1ppm d, where d is the baseline length (KM).

(3) Scope of application: establishment of global or national geodetic control network, crustal movement monitoring network, long-distance calibration baseline, joint survey between islands and mainland, borehole positioning and establishment of precision engineering control network, etc.

(4) Note: All observation baselines should form a series of closed graphs (as shown in Figure 8- 10) to facilitate field inspection and improve the reliability of results. And can be adjusted to further improve the positioning accuracy.

2. Fast static positioning

(1) operation method: select a reference station in the middle of the survey area, install a receiving device, and continuously track all visible satellites; Another receiver will set up a mobile station at each point in turn and observe each point for a few minutes. The work arrangement is shown in Figure 8- 1 1.

(2) Accuracy: The median baseline error of the rover station relative to the reference station is 5 mm1ppm d. ..

(3) Application scope: establishment and encryption of control network, engineering survey, cadastral survey, and location of a large number of points about 100 meters apart.

(4) Precautions: There should be more than 5 satellites for observation during the measurement period; The distance between the flow point and the reference point should not exceed 20 kilometers; ; The receiver on the mobile station does not need to keep track of the measured satellite when transmitting, so it can turn off the power supply and reduce energy consumption.

(5) Advantages and disadvantages:

Advantages:? Fast operation speed, high precision and low energy consumption; Disadvantages: When the two receivers are working, they cannot form a closed graph (as shown in Figure 8- 1 1), and the reliability is poor.

3. Quasi-dynamic positioning

(1) operation method: select a reference point in the survey area and arrange a receiver to continuously track all visible satellites; Put another mobile receiver at 1 station for observation (as shown in Figure 8- 12); Observe that the mobile receiver clicks for several seconds at 2, 3, 4 ... respectively while keeping the continuous tracking of the satellite under test without losing the lock.

(2) Accuracy: The median error of the baseline is about 1 ~ 2 cm.

(3) Scope of application: encryption control survey, engineering survey, field detail survey and line survey.

(4) Precautions: When observing, make sure that there are more than 5 satellites available for observation; The distance between the flow point and the reference point shall not exceed 20? Kilometers; During the observation, the mobile receiver shall not be unlocked, otherwise the observation time will be extended 1 ~ 2 min at the unlocked mobile point.

4. Set up the round-trip repeater station

(1) operation method: establish a reference point and place the receiver to continuously track all visible satellites; The mobile receiver goes to each point in turn to observe1~ 2 min; After 1 hour, reversely measure each flow point 1 ~ 2 minutes. The layout of the station is shown in Figure 8- 13.

(2) Accuracy: the baseline median error relative to the reference point is 5 mm+1ppm.d. ..

(3) Application scope: control survey and control network encryption, instead of traverse survey, triangulation and cadastral survey engineering survey machines.

(4) Note: The distance between the flowing point and the reference point shall not exceed15 km; ; The sky above the reference point is wide, and three or more satellites can be tracked normally.

5. Dynamic positioning

(1) operation method: establish a reference point and place the receiver to continuously track all visible satellites; The mobile receiver first observes statically for several minutes at the starting point; Then, the mobile receiver moves continuously from the starting point; Automatically move the real-time position of the vehicle at specified time intervals. The work arrangement is shown in Figure 8- 14.

(2) Accuracy: the instantaneous accuracy relative to the reference point is 1 ~ 2 cm.

(3) Application scope: accurately determine the trajectory of moving targets, determine the road center line, profile measurement, channel measurement, etc.

(4) Precautions: observe 5 satellites synchronously and track at least 4 satellites continuously; The distance between the flow point and the reference point shall not exceed 20? Kilometers

6. Operation mode and application of real-time dynamic measurement

(1) RTK positioning technology

Real-time dynamic (real? Time? Kinematics -RTB) measurement technology is real-time differential GPS(RTD? GPS measurement technology, which is a new breakthrough in the development of GPS measurement technology.

The basic idea of real-time dynamic measurement is to install a GPS receiver on the baseline, continuously measure all visible GPS satellites, and send their observation data to the user observation station in real time through radio transmission equipment. At the subscriber station, the GPS receiver receives the observation data sent by the reference station through the radio receiving equipment while receiving the GPS satellite signal, and then calculates and displays the three-dimensional coordinates and their accuracy of the subscriber station in real time according to the relative positioning principle.

(2)RTK operation mode and its application

According to the requirements of users, the working modes currently used for real-time dynamic measurement mainly include:

① Fast static measurement

Using this measurement mode, the GPS receiver is required to observe statically at each subscriber station. During the observation process, the knowledge of the whole weekend and the three-dimensional coordinates of the user station are solved in real time by combining the received synchronous observation data of the reference station. If the change of the solution results tends to be stable and its accuracy has met the design requirements, the observation can be ended in time.

When working in this mode, the receiver of the subscriber station does not need to keep tracking the GPS satellite continuously during the flow, and its positioning accuracy can reach 1 ~ 2 cm. This method can be applied to control survey, engineering survey and cadastral survey in cities, mines and other areas.

② Quasi-dynamic measurement

This measurement method, like the general quasi-motion measurement, usually requires the mobile receiver to observe at a certain starting point before the observation begins, and to initialize the work in real time by quickly solving the integer unknown quantity. After initialization, the mobile receiver of each observation station only needs to save the epoch of the observation signal and calculate the three-dimensional coordinates of the mobile station in real time together with the synchronous observation data of the reference station. At present, its positioning accuracy can reach centimeter level.

This method requires the receiver to keep continuous tracking of the measured satellite during the observation process. Once the lock is lost, it needs to be initialized again.

Quasi-dynamic real-time survey mode is usually mainly used in cadastral survey, detail survey, route survey and engineering lofting.

③ Dynamic measurement

In the dynamic measurement mode, it is generally necessary to observe for a few minutes at a certain starting point before initialization. After that, the mobile receiver automatically observes at a predetermined sampling time interval, and together with the synchronous observation data of the reference station, the spatial position of the sampling point is determined in real time. At present, its positioning accuracy can reach centimeter level.

This measurement mode still needs to continuously track the observation satellites during the observation process. Once the lock is lost, it needs to be initialized again. At this time, for the moving targets on land, we can observe them for a few minutes at the observation point where the satellite is out of lock, so as to reinitialize them, or we can use the dynamic initialization (AROF) technology to reinitialize them, while for the moving targets on the sea and in the air, we can only use AROP technology to reinitialize them.

Real-time dynamic measurement mode is mainly applied to real-time positioning of sampling points, aerial survey, road centerline survey and accurate navigation of moving targets in aerial photogrammetry and aerial geophysical exploration.