RTK mobile station (such as unmanned aerial vehicles, mapping engineering equipment) comprehensive GNSS navigation satellite navigation bar data and RTK fixed stationary station (such as fixed communication base station, mobile communication base station) to give differential data to carry out the correction, and then obtain instantaneous, high precision cell phone positioning services.
RTK accurate positioning technology
Before the RTK mobile station (UAV, mapping engine) enters the state of positioning and navigation (i.e., RTK), it first experiences three states successively, i.e., [NONE], [Single] and [Float].
When the RTK mobile communication base station is constructed by the method of “high precision point collection”, before it enters the state of broadcasting positioning and navigation data (i.e., [FIX]), it first experiences four states successively, namely, [NONE], [Single], [Float], and [RTK].
Basic concept:
[NONE] indicates that the RTK server (GNSS RTK Control Module or RTK Intelligent Instant Differential Meter) of the mobile station does not receive GNSS satellite signals, or the number of GNSS communication satellites received is too small to make corrections.
[Single] Indicates a point-and-shoot condition, where the RTK server at the mobile station receives a smooth and sufficient satellite signal, but does not receive the RTCM differential data broadcast by the RTK stationary station, and is in a separate (point-and-shoot), low-precision, accurate positioning state.
[ Float ] indicates: fluctuation state, the number of common communication satellites between RTK server of mobile station and RTK server of stationary station (RTK intelligent instantaneous differential instrument) is not enough, the common satellite signals are unstable, or the RTCM differential data received is unstable, which causes the result of the correction of RTK server of mobile station to fluctuate and unstable, and it is not possible to enter into the state of positioning and navigating.
[RTK] shows that in the instantaneous positioning and navigation state, the RTK server of the mobile station and the RTK server of the stationary station share sufficient and stable satellite signals, and the RTCM differential data received are stable and reasonable. The mobile station is in the state of instantaneous, high-precision and accurate positioning.
[ FIX ] indicates: static data broadcasting state, the RTK server of the stationary station can broadcast smooth and reasonable RTCM differential data according to the broadcasting station, or 3/4G communication carrier internet.
According to the above detailed introduction, we should understand that whether the RTK server of the mobile station can enter the [ RTK ] state or not, the key lies in two elements: one is whether the shared satellite signal of the mobile station and the stationary station is smooth and sufficient, and the other is whether the RTCM differential data received by the cell phone station is smooth and reasonable.
I. Shared communication satellite:
Because the RTK mobile station and stationary station spacing between a certain distance, and mobile station in the state of moving, and therefore stationary station and mobile station is located in the indoor environment is different, resulting in the two common satellite signal in the state of change.
Shared communications satellite
When the shared satellite signal between the two cannot be corrected, the RTK server of the mobile station will not be able to enter or exit the [RTK] state.
General influencing factors:
1、Temperature：If the temperature difference between the fixed station and the mobile station is very big.
2, interference signals: such as moving the station fitness movement in the whole process near high-voltage lines and other strong interference signals.
3, terrain and landscape: such as mobile station fitness exercise in the course of the near high and large engineering buildings, windbreak forests, large-scale rivers and so on.
Second, RTCM differential data:
Broadcast category:
RTCM Differential Data is broadcasted based on two separate data links of radio broadcasting stations and 3/4G communication carriers internet.
The broadcasting link of the data is not the same as its coverage area also has a certain difference, the broadcasting radio (RF) coverage area is: wide visibility spacing of 3 km.
Cloud RTK coverage area lies in the coverage area of the communication operator, theoretically it can cover the whole world, but the rated range is generally 70 km.
Reasonable range:
The level of accuracy of the Poleflight RTK cellular positioning system is 1 cm 1ppm (i.e. (10 1 × 0.000001 × D ) mm), which means that for every 1 km increase in the spacing of fixed stationary stations, the market positioning deviation of the mobile station will increase by 1 mm.
The influence level around the stationary station and the surrounding environment of the mobile station are also factors affecting the effectiveness of RTCM differential data. Usually, the reasonable spacing of RTCM differential data is 50km (the accuracy level of the wide zone of 50~70km has been tested to be in the acceptable range, so the limit of the extreme flight is open to the public up to 70km).
Data Scope
When the RTK mobile station exceeds the broadcast range or reasonable range of the RTK stationary RTCM differential data, the RTK server of the mobile station will not be able to enter or exit the [RTK] state.
General influencing factors:
1, spacing: the distance is getting farther and farther the broadcast network signal is weaker and the accuracy level is worse.
2, interference signal: the greater the impact of the broadcast scope and the smaller the reasonable scope.
Terrain: The more complicated (not wide) the natural environment is, the more harmful it is to RTCM differential data.
In general, in the case of each machine and equipment all normal, there are still many elements (such as temperature, interference signals, spacing, the natural environment, etc.) restraining the RTK mobile station can not be all normal into the [ RTK ] state.
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