Matrix 908 Field Computer
37
98-01578-EN R0
GGA Quality Indicator Information
►GPS – single point uncorrected position data based on GPS only with a GGA QI of "1" is accepted.
NOTE: GPS is always selected.
►GPS+GLONASS – single point uncorrected position data based on GPS and GLONASS with a GGA QI of "1" is accepted.
►GPS+SBAS – either single point uncorrected or SBAS corrected position data are accepted - GGA QI of "1" or "2" (3, 4 or 5 are also
accepted).
►GPS+SBAS – either single point uncorrected or SBAS corrected position data are accepted - GGA QI of "1" or "2" (3, 4 or
5 are also accepted).
►GPS+SBAS+DGPS – only GGA data with a QI value of "2" or higher is accepted (3, 4 or 5 are also accepted).
NOTE: All console based mapping, application and guidance functions are ceased if the GGA QI value drops below "2" with this
setting checked.
GNSS GLOSSARY
Commercial Satellite Provider:
Another common source for DGPS signals. Error correction information obtained from their base stations is sent to a communications satellite
(separate from the GPS satellites) and broadcast to the user. These satellite-based corrections tend to have more widespread coverage than
tower-based broadcasts (FM links), and system accuracy is not greatly affected by the user’s distance from the base station receivers. Most
of these service providers require a subscription fee for use. A commonly known provider is OmniSTAR.
CORS (Continuously Operating Reference Station)/Network RTK:
A series of base stations spread across a given geographic region (such as an entire state/county) that are networked via a centralised computer
and which broadcast RTK correction data over the Internet. CORS networks may be publicly or privately owned/operated and may offer a free
signal or require an annual subscription fee. By accessing a CORS network via a cellular connection, the end-user eliminates the need to own a
base station.
Differential Corrections
Differential corrections is a solution specific to the "double-differencing" algorithm used to determine the correction values applied by RTK to each
GNSS satellites range data. "Corrections" is the generic term applied to all forms of potential corrections from SBAS (WAAS/EGNOS) through to
OmniStar, TerraStar PPP and RTK.
Differential GPS (DGPS):
Use of the specific RTK solution to apply differential corrections to the GPS satellite constellation data.
EGNOS (European Geostationary Navigation Overlay Service):
A satellite based augmentation system (SBAS) developed jointly by the European space agency (ESA), European community and
EUROCONTROL. The system is free to use and provides differential correction coverage primarily across the European continent. EGNOS
delivers pass-to-pass accuracies of 15-25 cm and year-to-year accuracies of +/-1 m.
GLONASS (Global Navigation Satellite System):
A global satellite navigation system developed and operated by the Russian government. It is composed of approximately 24 satellites which
continuously orbit the earth. While early GNSS receivers typically utilised only GPS signals, many of today’s GNSS receivers can utilise
signals from both GPS and GLONASS, effectively increasing the total number of satellites available for use.
GNSS Precise Point Positioning (PPP)
PPP is a subscription based globally provided satellite correction service broadcast to properly equipped GNSS receivers. PPP utilises a
global array of reference stations to correct for satellite clock and orbit errors which are then broadcast to local receivers. PPP does require a
convergence time.
