User's Manual
Page
58
X360 GIS Reference
Receiver
User
Guide
D.
Glossary
three-dimensional measurements. Other DOP values include VDOP (vertical
DOP)
and HDOP (Horizontal Dilution of Precision).
Using a maximum PDOP value is ideal for situations where both vertical
and
horizontal precision are important.
postprocessing
Postprocessing is the processing of satellite data after it has been collected,
in
order to eliminate error. This involves using computer software to compare
data
from the rover with data collected at the base station.
real-
time
differen
tial
GPS
Also known as real-time differential correction or DGPS. Real-time differential
GPS
is the process of correcting GPS data as you collect it. Corrections are
calculated at
a base station and then sent to the Receiver through a radio link.
As the rover
receives the position it applies the corrections to give you a very
accurate position
in the field.
Most real-time differential correction methods apply corrections to code
phase
positions. RTK uses carrier phase measurements.
While DGPS is a generic term, its common interpretation is that it entails the
use
of single-frequency code phase data sent from a GPS base station to a
rover GPS
Receiver to provide sub-meter position accuracy. The rover
Receiver can be at a
long range (greater than 100 km (62 miles)) from the
base station.
station
See base station
rover
A rover is any mobile GPS Receiver that is used to collect or update data in
the
field, typically at an unknown location.
RTCM
Radio Technical Commission for Maritime Services. A commission established
to
define a differential data link for the real-time differential correction of
roving GPS
Receivers. There are three versions of RTCM correction messages.
All CHC GPS
Receivers use Version 2 protocol for single-frequency DGPS type
corrections.
Carrier phase corrections are available on Version 2, or on the newer Version
3
RTCM protocol, which is available on certain CHC dual-frequency
Receivers. The
Version 3 RTCM protocol is more compact but is not as
widely supported as
Version 2.
RTK
Real-time kinematic. A real-time differential GPS method that uses carrier
phase
measurements for greater accuracy.
signal-to-
noise
ratio
SNR. The signal strength of a satellite is a measure of the information content
of
the signal, relative to the signal’s noise. The typical SNR of a satellite at 30°
elevation is between 47 and 50 dBHz. The quality of a GPS position is
degraded if
the SNR of one or more satellites in the constellation falls below
39.
skyplot
The satellite skyplot confirms reception of a differentially corrected GPS signal
and
displays the number of satellites tracked by the GPS Receiver, as well as
their
relative positions.
SNR
See signal-to-noise ratio
UTC
Universal Time Coordinated. A time standard based on local solar mean time
at
the Greenwich meridian.
VRS
Virtual Station. A VRS system consists of GNSS hardware, software, and