Trimble Outdoors 5700 - Manual (Page 106)

8 Real-Time Kinematic (RTK) Surveying
9 0 5700 GPS Receiver User Guide
Appl
icatio
ns
8.1
Introduction
The 5700 receiver is designed for high-precision navigation and
location. It uses Real-Time Kinematic (RTK) techniques to achieve
centimeter-level positioning accuracy. This chapter introduces RTK
concepts and terminology, and provides instructions for setting up the
5700 receiver as a reference or rover receiver for RTK surveying.
8.2
Real-Time Kinematic Positioning
Real-Time Kinematic (RTK) positioning is based on at least two GPS
receivers—a reference receiver and one or more rover receivers. The
reference receiver takes measurements from satellites in view and then
broadcasts them, with its location, to the rover receiver(s). The rover
receiver also collects measurements to the satellites in view and
processes them with the reference station data. The rover then
estimates its location relative to the reference. Typically, reference and
rover receivers take measurements at regular 1-second epochs (events
in time) and produce position solutions at the same rate.
8.2.1
Carrier Phase Initialization
The key to achieving centimeter-level positioning accuracy with RTK
is the use of the GPS carrier phase signals. Carrier phase
measurements are like precise tape measures from the reference and
rover antennas to the satellites. Although carrier phase measurements
are very precise, they contain an unknown bias, termed the integer
cycle ambiguity, or phase ambiguity. The 5700 receiver rover has to
resolve, or initialize, the carrier phase ambiguities at power-up and
every time the satellite signals are interrupted.
The 5700 receiver can automatically initialize the carrier phase
ambiguities provided that at least five common satellites are being
tracked at the reference and rover sites. Automatic initialization is
sometimes termed on-the-fly (OTF), to reflect the fact that no
restriction is placed on the motion of the rover receiver throughout the
initialization process.