art_000049;What is PPP - Precise Point Positionning

What is PPP - Precise Point Positioning

Precise point positioning (PPP) is a method that performs precise position determination using a single GPS receiver.

This positioning approach arose from the advent of widely available precise GPS orbit and clock data products with centimetre accuracy. These data can be applied to substantially reduce the errors in GPS satellite orbits and clocks, two of the most significant error sources in GPS positioning.

Combining precise satellite positions and clocks with a dual-frequency GPS receiver (to remove the first order effect of the ionosphere), PPP is able to provide position solutions at centimetre to decimetre level, which is appealing to many applications such as airborne mapping. PPP is different from double-difference RTK (real-time kinematic) positioning that requires access to observations from one or more base stations with known coordinates. The word “precise” is also used to distinguish it from the conventional point positioning techniques that use only code or phase-smoothed code as the principal observable for position determination.

In Post-Processing, Precise orbits and clocks data, as generated by International Organizations (IGS, Canadian Natural Resources, Center for orbit Determination in Europe (CODE), etc.) has to be used in the calculation. In a way, Precise Orbits and Clocks are replacing Base Station data as used in standard differential positioning.

EZSurv can process static as well as kinematic data in PPP mode. We can do this using L1/L2 data or L1 only data. The best possible GNSS accuracy, a few centimeters or better, is obtained by using carrier phase measurements from dual-frequency receivers. However, single-frequency receivers can provide decimeter accuracy at a reduced cost for the receiver (when appropriate observation periods are available). Precise Orbit and Clock files are automatically downloaded from research center. EZSurv offer the same level of accuracy than all those online PPP services.

Post-process PPP as implemented in EZSurv is similar, in term of accuracy, to Real Time System like Fugro’s Omnistar, Trimble’s CenterPoint RTX, Navcom’s StarFire and Veripos. Typically, Post-Processing will deliver better accuracy since the calculations made in the software take the advantages of the filtering/smoothing techniques.

Long initialization time is currently a PPP limitation in many applications. Typically, for surveying when signal obstruction is present during regular survey jobs, PPP is not suitable.

Typical accuracy and latency of IGS products

Article: 000049