RTK difference with the RTD, is a carrier phase, a differential code is, the RTK positioning accuracy and higher.
The difference between RTK and PPK, and provide a real-time data, is a post-processing.
WAAS SBAS system is a particular example, included in the SBAS system.
01 RTD
RTD: English name Real Time Differential, Chinese meaning is real-time dynamic code phase differential technology. The method of working is the reference station pseudorange (or coordinate) a correction value (difference value) sent to the user receiver, the method calculates the precise location of the user receiver according to the observed value difference value itself.
When measured before using RTK, CORS will be red when connected RTD comes first, and then the RTK fixed. In fact, RTD and RTK is the same on some principle, so small series here on talk together.
First of all from the same place in terms of level, RTD (Real Time Differential) and RTK (Real Time Kinematic) are of differential GPS is DGPS, and in real time, dynamic, relative positioning.
Then different places, RTD pseudorange calculation, based on the coordinates of each base station and the known coordinates of the satellite, each satellite is determined every time the real distance to the reference station. And then compared with the measured distance dummy, derived pseudorange corrections, be transmitted to the user receiver, it belongs to the code (C / A code, P code) difference technique.
And the calculated two RTK carrier phase observations stations, i.e. base station is issued to the user the collected carrier phase receiver, the difference is evaluated solver coordinates. Belonging to the carrier (L1, L2, L5) phase difference technique.
Real-time dynamic measurement, differential techniques first introduced in the code phase measurements, so the real-time dynamic code phase difference measurement referred to a conventional differential GPS measurement techniques. That is the general DGPS / differential positioning.
Because RTD using pseudorange measurements, so that only the lower sub-meter, typically user non-car navigation art high-precision positioning accuracy.
02 SBAS
SBAS: English name Satellite-Based Augmentation System, Chinese meant Wide Area Augmentation System difference, if you do not know what this means, then say satellite-based augmentation system we all know. Wide Area Augmentation System is the differential satellite-based augmentation system.
SBAS GNSS augmentation belong to one, in a satellite-based enhanced system, relatively speaking, as well as ground-based augmentation system GBAS and ABAS-based augmentation system aircraft. If you want to learn more about, you can refer to the previous article Xiaobian: up knowledge and understanding about the satellite-based augmentation systems and ground-based augmentation system. " Xiao Bian here simply to talk about SBAS.
SBAS system is to achieve an enhanced system for improving the positioning accuracy of the existing satellite navigation system born, mainly consists of four parts: the ground reference base station, the master station, and upload the geostationary satellite station and the like. We look at the works:
By a large difference are very widespread station (known position) of the satellite navigation monitor, to obtain raw location data (pseudorange, carrier phase measurement, etc.) and sent to the central processing facility (master station), which is obtained by calculating various positioning purpose each satellite correction information sent by the GEO satellite uplink injection station, and finally the correction information is broadcast to users, so as to improve positioning accuracy
Currently countries around the world have established a perfect SBAS systems, including the US WAAS, EGNOS in Europe, Japan MSAS and India's GAGAN.
But SBAS mainly used in aviation and maritime, rarely used satellite-based augmentation system we usually measure to use is the main ground-based augmentation system. About satellite-based systems and ground systems can refer to the article before the small series.
03 WAAS
As I said before Xiao Bian, WAAS is a kind of SBAS Wide Area Augmentation System, WAAS stands for Wide Area Augmentation System, translated Wide Area Augmentation System, by the US Department of Transportation (DOT) and the Federal Aviation Administration (FAA) jointly a system development, mainly used in aerospace applications, such as GPS navigation and other aircraft.
WAAS is to address the emergence of GPS can not provide a very accurate height for the aircraft heading information and guidance, as well as the distance from the runway elevation information at all points along the approach. Prior U.S. empty tube portion is mainly used ILS (instrument landing system) and MLS (microwave landing system), the former is difficult and cumbersome embodiment, the latter development process, GPS receivers began to appear.
WAAS consists of three main parts: the ground segment, the space segment and the user segment. Ground stations receiving part of the reference and monitoring the GPS signal, and correct the correction, and then sent to the space segment of the satellite broadcast to the user to re-segment.
WAAS improves the positioning accuracy of the emergence of aircraft navigation, but also reduces the cost of the construction cost of the airport navigation facilities, and a single receiver mounted on the aircraft.
04 PPP
PPP stands for Precise Point Positioning, translated into precise point positioning, is also called point positioning absolute positioning, precise point positioning is the use of carrier-phase observations and high accuracy provided by organizations such as IGS satellite ephemeris and satellite clock errors method of performing high-precision single point positioning.
Xiao Bian also refer to the previous article, "Understanding PPP and ground-based augmentation system enhancements PPP technology."
PPP technology later than RTK technology appears, PPP is another technological revolution after the GNSS positioning technology relay RTK / Network RTK technology that has changed the past can only use differential positioning mode to achieve high-precision positioning situation for global high-precision GNSS positioning provides an effective method.
The planar positional accuracy of the current PPP point of the observation value obtained up to day 13cm, height accuracy of up to 24cm.
05 PP accused
PPK Full Post Processed Kinematic, with a corresponding RTK positioning technology, the use of which is a carrier-phase observations for post-processing dynamic relative positioning technology, the real-time RTK.
Because post-processing is carried out, so the user need not equipped with data communication link (you can save the cost of traffic), the observation is more convenient, free, suitable for real-time applications without the need to obtain positioning results.
06 Wide Area Augmentation
I.e. the WADGPS Wide Area Differential GPS, is a kind of differential GPS, Differential GPS according to the classification of the same model as well as the principles of the single local area differential GPS reference station and a plurality of differential GPS reference station.
Why is there wide-area differential GPS it? As the name suggests, when the differential GPS need to cover a large area (For when covering the Chinese mainland and adjacent waters), single base stations and base stations of local area differential GPS encounter some difficulties, the need to establish a large number of base station group network, time-consuming and money. Secondly, some places can not establish a base station and a signal transmitting station, will produce a large blank area.
So this time, a wide area differential GPS technology came out in a relatively large area, it is uniformly laid to form a small number of base stations sparse differential GPS network, each base station independently transmits the data observed and the observed value processing center, unified processing by a data processing center, in order to separate the various errors.
The satellite ephemeris and corrections, satellite clock corrections, and atmospheric difference between the clock delay models advertised to the user, such a system is referred to as wide-area differential differential system.
Like Global Differential GPS (World-wide DGPS) is part of a special case of wide-area differential GPS. Xiao Bian above mentioned technology is WAAS wide area differential GPS technology, and to further improve and supplement the wide-area differential GPS technology.
07 summary
On the relationship and differences between the several techniques summarize here RTK, RTD, PPK, SBAS, WAAS belong differential GPS technology. PPP belong to single point positioning (absolute positioning non-differential).
A summary of these technology names due to differences in classification is based upon different standards and understanding, the current name on different reference materials used by confusing the situation with the same name or a different name synonymous different meaning may appear to be Notice the difference.
