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OS Net glossary

aGPS 

Assisted GPS – provides supplementary information enabling reduced ‘time to first fix’ so that users get position very quickly at power on. This technique is used in low-end GPS equipment/applications (for example, to LBS market, tracking and so on).

dGNSS

Differential GNSS – a form of corrected GNSS giving enhanced accuracy in the few decimetre range (better than stand alone GNSS, not as good as RTK).

Several GNSS services are available:

General Lighthouse Authority beacons – Free service. External radio receiver (separate from GPS unit) usually required to obtain the corrections.

EGNOS – European Geostationary Navigation Overlay Service. See below.

OS Net® – partners offer GNSS services based on the data streams of the Ordnance Survey® OS Net permanent GNSS network.

EGNOS

European Geostationary Navigation Overlay Service – providing GNSS augmentation. Consisting of three geostationary satellites and a network of ground stations, EGNOS will achieve its aim by transmitting a signal containing information on the reliability and accuracy of the positioning signals sent out by the GPS. It will allow users in Europe and beyond to determine their position to better than 5 m compared with about 10 m at present. Free service. Now built into many GPS receivers, so no additional equipment required.  Can be difficult to receive signal in harsh environments (tall buildings and so on). See http://www.esa.int/esaNA/egnos.html

Galileo

The developing European GNSS.

GLONASS

Global'naya Navigatsionnaya Sputnikovaya Sistema – Russian GNS. Now being improved and expanded after years of falling into disrepair.

GNSS

Global Navigation Satellite System – Generic term for systems such as GPS and Galileo.

GPRS

General Packet Radio Service – a non-voice data service for the mobile telephone network.

GPS

Global Positioning System – US owned positioning satellite constellation. Gives 10 to 20 m accuracy as standard.

GSM

Global System for Mobile communications – a non-voice data service for the mobile telephone network. Predates GPRS and currently enjoys more than 71% of the world mobile non-voice market.

Inverse dGPS  

Inverse dGPS takes a user’s coordinates (obtained by simple GPS) and improves them by using models based on data from permanent GPS receivers (for example, OS Net). Using this technique a user could be equipped with a simple (therefore cheap and power-efficient) GNSS receiver. The user’s position is sent to a central control hub where it is improved using Inverse dGNSS. A day’s worth of GNSS positioning data can be sent in at once, for example, negating the need for a permanent communication link to the user. An example application of this technique could be in road-user charging.

OSGB36®

Ordnance Survey’s National Grid coordinate system.

OS Net

Ordnance Survey’s identity for its internal GPS correction network.

RINEX

Receiver INdependent EXchange format – a set of standard definitions and formats that permits post-processing of GPS position information. Just as accurate as RTK but not real time.

RTCM

Radio Technical Commission for Maritime Services – an industry standard format for GPS data exchange based on real-time data.

RTK     

Real Time Kinematic – a form of corrected GPS giving accuracy down around 20 mm.
A-S Anti-spoofing
C/A-code coarse/acquisition-code
CEP circular error probable
DGPS differential GPS
DOP dilution of precision
ECEF Earth-centered-Earth-fixed
FOM figure of merit
Galileo European Global Navigation Satellite System under development
GDOP geometric dilution of precision
GLONASS Global Navigation satellite system
GMT Greenwich Mean Time
GPS Global Positioning System
HDOP horizontal dilution of precision
HOW hand over word
INS Inertial Navigation System
L1 GPS primary frequency, 1575.42 MHz
L2 GPS secondary frequency, 1227.6 MHz
MSL mean sea level
MTBF mean time between failure
NMEA National Marine Electronics Association
P-code precise code
PDOP position dilution of precision
PPM parts per million
PPS Precise Positioning Service
PRN pseudo random noise
RF radio frequency
RINEX Receiver Independent Exchange Format
RMS root mean square
RSS root sum square
RTCA Radio Technical Commission for Aeronautics
RTCM Ratio Technical Commission for Maritime Services
RTK Real-Time Kinematic
SA Selective Availability
SEP spherical error probable
SPS Standard Positioning Service
TAI International Atomic Time
tdOP time dilution of precision
TTFF time to first fix
UT Universal Time
UTC Universal Time Coordinated
VDOP vertical dilution of precision
WGS84 World Geodetic System 1984
1 PPS 1 pulse per second

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