Differential GPS RTK thousand search

Catalog

GPS and GNSS The difference between ：

Difference GPS Positioning principle ：

1. Position difference principle （ A little ）

2. Pseudo range difference principle （DGPS）

3. Carrier phase difference principle （RTK）（ a key ）

Chihiro position

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GPS and GNSS The difference between ：

GPS： Refers to global positioning system (Global Positioning System）;
GNSS： Global satellite navigation system （Global Navigation Satellite System）, It's the Beidou System 、GPS、GLONASS、Galileo System and other single satellite navigation and positioning systems .

Difference GPS Positioning principle ：

Ordinary single point positioning technology is affected by the ionosphere due to the propagation of satellite signals in space 、 Troposphere, etc , The signal propagation has a certain refraction , It brings pseudo range observation error , Make the positioning accuracy in 5 To 10 Rice range . Differential positioning technology can eliminate the pseudo range measurement error , Effectively improve positioning accuracy . For all users in the same area , The errors caused by satellite signal propagation through the atmosphere are correlated , It can be considered that the errors are equal , The reference station calculates these measurement error values , It is transmitted to the mobile station through the network , So as to eliminate the GPS Measurement error value , Improve the accuracy of measurement and positioning . Differential enhancement technology is GNSS A complement to positioning , It can effectively improve the positioning accuracy .

GPS Positioning is to use the pseudo range of a group of satellites 、 Ephemeris 、 Satellite launch time and other observation values , At the same time, we must know the clock difference of users . therefore , To get the three-dimensional coordinates of the ground point , Must be right 4 A satellite to measure .

In this process , There are three parts of error . One part is shared by each user receiver , for example , Satellite clock error 、 Ephemeris error 、 Ionospheric error 、 Tropospheric error, etc ; The second part is the propagation delay error that cannot be measured by the user or calculated by the correction model ; The third part is the inherent error of each user receiver , For example, internal noise 、 Channel delay 、 Multipath effect, etc . Using differential technology , The first part of the error can be completely eliminated , Most of the errors in the second part can be eliminated , It mainly depends on the distance between the reference receiver and the user receiver , The third part of the error cannot be eliminated .

According to the difference GPS The information sent by the reference station can be differential GPS Positioning is divided into three categories , namely ： Position difference 、 Pseudo range difference and carrier phase difference . The working principle of these three kinds of difference methods is the same , That is, the reference station sends correction data , The user station receives and corrects the measurement results , To obtain accurate positioning results . The difference is , The specific content of sending correction data is different , Its differential positioning accuracy is also different .

1. Position difference principle （ A little ）

This is the simplest difference method , Any kind of GPS The receiver can be refitted and composed of this differential system . Installed on the reference station GPS Receiver observation 4 Three dimensional positioning can be carried out after a satellite , Calculate the coordinates of the reference station . Due to orbital errors 、 Clock error 、SA influence 、 Atmospheric effects 、 Multipath effect and other errors , The calculated coordinates are different from the known coordinates of the reference station , There is an error . The reference station uses the data link to send the correction number , Received by the subscriber station , And the user station coordinates solved by it are corrected .
Finally, the corrected user coordinates have eliminated the common error between the reference station and the user station , For example, satellite orbit error 、 SA influence 、 Atmospheric impact, etc , The positioning accuracy is improved . The above prerequisite is the observation of the same group of satellites by the base station and the user station . The position difference method is suitable for the distance between the user and the reference station 100km Within the .

2. Pseudo range difference principle （DGPS）

At present, it is most widely used .
The receiver at the reference station requires its distance to the visible satellite , The calculated distance is compared with the measured value with error . Using a α-β The filter filters the difference and calculates its deviation . Then the ranging errors of all satellites are transmitted to the user , The user uses this ranging error to correct the measured pseudo range . Last , The user uses the corrected pseudo range to solve his own position , The public error can be eliminated , Improve positioning accuracy .
Similar to position difference , The pseudo range difference can offset the common error of the two stations , However, with the increase of the distance from the user to the reference station, there is a systematic error , This error cannot be eliminated by any difference method . The distance between the user and the reference station has a decisive impact on the accuracy . Using pseudo range difference method , The positioning accuracy can reach sub meter level .

3. Carrier phase difference principle （RTK）（ a key ）

It is a difference method for real-time processing the carrier phase observation of two measurement base stations , Send the carrier phase collected by the reference station to the user receiver , Calculate the difference and calculate the coordinates .RTK Technology can provide three-dimensional coordinates of observation points in real time , And reach cm Class high accuracy .

RTK Positioning principle ： Will be located on the reference station GPS Satellite data observed by the receiver , Through the data communication link （ Radio station ） Send it out in real time , And the mobile station located nearby GPS While observing the satellite, the receiver , It also receives radio signals from the reference station , Through the real-time processing of the received signal （ That is, the same error term is eliminated by difference ）, Give the three-dimensional coordinates of the mobile station , And estimate its accuracy .

utilize RTK When measuring , At least two sets are equipped GPS Receiver , One is fixed on the reference station , The other is used as a mobile station for point measurement . There is also a data communication link between the two receivers , Send the observation data on the base station to the mobile station in real time . For the data received by the mobile station （ Satellite signal and reference station signal ） Real time processing also requires RTK Software , It mainly completes the solution of double difference ambiguity 、 Solution of baseline vector 、 Coordinate conversion .

RTK Technology can achieve centimeter level positioning accuracy in a very short time , It is widely used in mapping control measurement 、 Construction setting out 、 Engineering survey, topographic survey and other fields . but RTK There are also some disadvantages , It is mainly manifested in the need to set up local reference stations , The error increases with the distance from the mobile station to the reference station .

This benchmark station can be built by itself , And then through UHF/4G Wait to establish contact with mobile devices , Suitable for use in fixed positions . If you travel long distances , You need to consider cross domain resource sharing （CORS,cross-origin resource sharing）, Most of them are used in China Chihiro position .

Chihiro position

Chihiro location provides the largest range of accurate positioning services in the country . Currently used by the public in the United States GPS The accuracy of navigation and positioning is 5-10 Meter scale , And compatible with Beidou /GPS The positioning accuracy of dual-mode public navigation terminals is also mostly 3-5 Rice or so , Chihiro position through the foundation reinforcement system , The positioning accuracy can be improved to centimeter level 、 Even static millimeter level .   
Positioning principle ： Chihiro position and GPS It's a different concept .GPS Mainly through satellite to locate , There is no positioning enhancement system , Due to the error of signal propagation , So the positioning accuracy is at the meter level ; Chihiro set up base stations in various regions , The main purpose of the base station is to modify the information error sent by the satellite , Make the positioning more accurate . Therefore, Chihiro position needs to cooperate with satellites to complete accurate positioning ; The accuracy level is at the centimeter level .
After the Chihiro Zhicun set meal is bought , There are two ways to use it ：
（1）appkey+appsecret（ secret key ）, Use the official SDK Development is relatively convenient ;
（2） Self set differential account + password , Used in general equipment such as 4G DTU in .
If you want to develop your own hardware or write code, just see SDK Integration Guide , Want to buy another house directly 4G DTU Then use , See the differential account Guide .
For the second, use a differential account + Differential password , Directly buy hardware developed by other manufacturers, such as 4G DTU, Generally single chip microcomputer +4G Module made it , It's all realized Ntrip Protocol to communicate , Insert a mobile phone card / IOT card , Set it slightly , It can be used when connected with inertial navigation , Several options are set as follows :
① Address domain name ：rtk.ntrip.qxwz.com or IP（60.205.8.49）
② port
port ：8001 Corresponding coordinate frame ITRF2008 Reference epoch 2016.0
port ：8002 Corresponding coordinate frame WGS84 Reference epoch 2005.0
port ：8003 Corresponding coordinate frame CGCS2000 Reference epoch 2000.0
③mountpoint/ Source / Mount point
RTCM32_GGB or RTCM30_GG
④ Differential account number
⑤ Differential code
Reference link