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PPP Standards
| Fundamentals | |
|---|---|
| Title | PPP Standards |
| Author(s) | GMV |
| Level | Basic |
| Year of Publication | 2011 |
Precise point positioning (PPP) stands out as an optimal approach for providing global augmentation services using current and coming GNSS constellations. PPP requires fewer reference stations globally distributed rather than classic differential approaches (e.g. RTK), also one set of precise orbit and clock data is valid for all users everywhere, and the solution is largely unaffected by individual reference-station failures. There are always many reference stations observing the same satellite because the precise orbits and clocks are calculated from a global network of reference stations. As a result, PPP gives a highly redundant and robust position solution.
PPP Standards
Precise Point Positioning (PPP) is a global precise positioning service, since it requires the availability of precise reference satellite orbit and clock products in real-time using a network of GNSS reference stations distributed worldwide.
There are not "PPP Standards" as understood in SBAS Systems (ref MOPS), but there are some conventions, models and formats commonly used. To achieve the highest accuracy and consistency, users must also implement the GNSS-specific conventions and models adopted by the IGS..[1]
This section describes the adjustment procedure and specifies the Earth and space based models and conventions that must be implemented to achieve mm-cm level positioning, tropospheric zenith path delay and clock solutions.
Developers of GPS software are generally well aware of corrections they must apply to pseudorange or carrier-phase observations to eliminate effects such as special and general relativity, Sagnac delay, satellite clock offsets, atmospheric delays, etc. All these effects are quite large, exceeding several meters, and must be considered even for pseudorange positioning at the meter precision level. When attempting to combine satellite positions and clocks precise to a few centimeters with ionospheric-free carrier phase observations (with millimeter resolution), it is important to account for some effects that may not have been considered in pseudorange or precise differential phase processing modes.
The following sections look at additional correction terms that are significant for carrier phase point positioning. They have been grouped under Satellite Attitude Effects, Site Displacements Effects and Compatibility Considerations. A number of the corrections listed below require the Moon or the Sun positions which can be obtained from readily available planetary ephemerides files, or more conveniently from simple formulas (as implemented here) since a relative precision of about 1/1000 is sufficient for corrections at the mm precision level. Note that for centimeter level differential positioning and baselines of less than 100 km, the correction terms discussed below can be safely neglected.
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