POST-processing

RTK / NRTK,
essential technologies in precision geolocation.

These terms are recurrent in precision geolocation and in the technology developed by TERIA. What do they mean and what are their differences?

RTK - Real Time Kinematic

RTK is a technical process for real-time transmission of corrections from a pivot to GNSS mobiles.

This technology makes it possible to remove ambiguities and thus provide centimetric precision positioning ( ambiguities: whole numbers of wavelengths in each satellite-receiver distance, unknown during phase measurement)

More concretely, it is not corrections that are transmitted, but rather the raw observations of the pivot.

The function of the mobile is to calculate the pivot-mobile vector. This calculation method requires a perfect geo-referencing of the pivot. Otherwise, all the points recorded are offset from the reference system.

NRTK - Network Real Time Kinematic

The NRTK consists in sharing the data of several fixed stations in a network. This data is communicated in real time to a server centre. It transmits to users modelled corrections for the entire coverage area. There are different types of corrections in NRTK: FKP – MAC – VRS (see our article on formats)

Chronologically, it was GEO++ (Germany) that initiated the FKP, the MAC by LEICA Geosystems and the VRS by TRIMBLE.

NRTK corrections are generally transmitted in RTCM, which is the standard format for the exchange of raw GNSS data.

Thus, at the origin of TERIA in 2005, RTCM 2.3 was the exchange format used with the only FKP data format (mounting point FKP01). In 2008, RTCM 3.1 replaced RTCM 2.3 to integrate GLONASS data, MAC format and standard messages on the calculation of residues in RSV.

This made it possible to provide two new types of corrections (MAC30 and PRS30 mounting points). Since 2018, RTCM 3.2 or also called RTCM MSM has taken over to also carry GALILEO and BEIDOU data.

The TERIA network has always had a policy of providing corrections adapted to customers’ GNSS equipment. This is done by providing the preferred corrections for each manufacturer as long as they meet the standards. For the same reasons, GALILEO and BEIDOU corrections are made available via RTCM 3.2. It should be noted that not all messages of RTCM 3.1 are yet adapted for GALILEO / BEIDOU in RTCM 3.2.

Technically there is an important philosophical difference between these three types of corrections.

To understand why these changes are necessary for certain uses,
here is an article on the fundamental principles of GNSS geolocation.

SEE THE ARTICLE

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