Precise Real-Time Positioning Using Network RTK - Global Navigation Satellite Systems: Signal,Theory and Applications - page 173

The drawbacks of the FKP method include the need of the rover to perform interpolation of
measurement corrections, possible inconsistency at the edge of two adjacent planes due to
the use of the linear plane surfaces, and large data formats are needed. In Radio Technical
Commission for Maritime services (RTCM) format version 3.1, FKP corrections can be sent
via message types 1034 and 1035 for GPS and GLONASS observations, respectively.

5.3 The Master-Auxiliary (MAC) method

In the Mac approach, the rover sends its approximate position via NMEA format to the
network processing centre. The centre determines for this specific user the appropriate
master station, which is usuall selected the closest reference station to its position, and
identifies the auxiliary reference stations. These stations are chosen within a catch circle of a
predefined radius (e.g. 70 km) around the rover, and with a pre-set number (e.g. from 3 to
14). Figure 3 illustrates the Mac concept. In one Mac approach, a network RTK of large
number of reference stations can be subdivided into clusters (Leica Geo systems, 2011). The
processing centre defines the appropriate cluster to a user and defines the appropriate
network corrections applicable to that user.

Aux k 4

Master j

Auxiliary k 1

rover

Aux k 3

Aux k 2

Fig. 3. The Master-Auxiliary NRTK

The rover can receive different types of information according to the strategy used by the
Mac processing centre which may include:

• The coordinates and raw measurements of the Master station.

• Measurement corrections at the Master station.

• Correction differences between the Master and Auxiliary stations. These differences

when being added to the corrections of the Master will give the corrections at the
Auxiliary stations.

The latter Mac corrections can be received via RTCM v3.1 message types 1014-1018, 1030-
1031 and 1034-1035 etc.

In Equations (7 and 8), the single observation differences between the Master station j and
an Auxiliary station k for satellite s reads (Takac and Lienhart, 2008):

∆R δ∆r

I δ∆r ∆T /λ

(20)