Specifications

Differential and RTK Operations 27
Differential and RTK
3
Differential and RTK Operations
Real-time differential positioning involves a reference (base) station receiver computing
the satellite range corrections and transmitting them to the remote stations. The reference
station transmits the corrections in real time to the remote receivers via a telemetry link.
Remote receivers apply the corrections to their measured ranges, using the corrected
ranges to compute their position.
RTK (Real-time kinematic) positioning can be used in lieu of real-time differential
positioning. RTK uses the carrier signal in addition to the code signal and is much more
accurate. Although messages transmitted and calculations performed vary, RTK is
essentially a special form of differential positioning. A base station receiver is required to
transmit RTK data to remote receivers. The remote receivers use the RTK data to compute
a corrected position.
As stand-alone, the receiver can compute a position to around 100 meters. Differential
GPS achieves sub-meter precision at a remote receiver, and RTK positioning achieves
centimeter accuracy at a remote receiver.
A communication link must exist between the base and remote receivers. The
communication link can be a radio link, telephone line, cellular phone, communications
satellite link, or any other medium that can transfer digital data.
RTK is also referred to as Carrier Phase Differential (CPD) in this manual.
Base Stations
Setting Up a Differential Base Station
You must have the Base option [B] installed on the receiver.
Send the commands listed in Table 3.1 to the receiver to generate RTCM differential
corrections using message type 1.
Table 3.1: Differential Base Station Commands
Command Description
$PASHS,RST Reset the receiver to factory defaults
$PASHS,PEM,4 Set the Base differential mask to four degrees
$PASHS,POS,ddmm.mmm,d,dddmm.mmm,d,saaaaa.aa Enter the phase center of the antenna if ANR is
OFF or CPD, or the ground mark if ANR is ON.