POS MV V5 Installation and Operation Guide
Theory
of Operation
Copyright © Applanix Corporation, 2017
B-23
Instead, POS MV uses carrier phase differential position measurements to determine the relative position
of one GNSS antenna with respect to the other.
Using this method, the differential position computed by GAMS for the two antennas has an accuracy of
between two and 10 millimetres, depending on the local multipath environment. The heading data
supplied can therefore exhibit accuracy of the order 0.1° to 0.5° RMS, depending on the multipath
environment and on the horizontal separation distance between the two antennas. Errors of this
magnitude are typical of installations where the antenna separation distance is between one and three
metres.
Figure 92 represents the signal from one satellite in the GNSS constellation received by the GNSS
receiver. The drawing shows the true position of the receiver, although the receiver knows this position
only to a finite limit of accuracy.
Pseudorange is the distance measured between the transmitting satellite and the receiver, based on the
correlation between the transmitted code and the local reference code in the receiver. This measurement
includes no correction for errors in synchronization between the satellite and the receiver clocks.
In the example in Figure 92, the predicted position is shown as calculated from the satellite pseudo-
range.
GNSS signals at the L1 frequency (1575.42 MHz) have a wavelength of 0.19 metres. A GNSS receiver
could compute its precise distance from a transmitting satellite if it knew two facts:
•
The exact number of integer wavelengths between the transmitter and the receiving antenna
•
The phase of the received signal
Although the GNSS receiver can measure the phase of the received signal, it cannot determine exactly
how many integer wavelengths exist between the transmitter and the receiving antenna. It knows this
value to within approximately one hundred cycles by knowing the satellite pseudo-range, but there
remains some uncertainty in its precise determination.