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) and OS Net may have a part to play here through providing raw GPS data to an aGPS service provider, who would then generate the aGPS information.

dGPS

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

Several dGPS 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.

OmniSTAR - see http://www.omnistar.com/. Subscription service using professional quality equipment. Positional accuracy generally better than 1 m.

OS Net -  partners may offer dGPS services based on the data streams of the Ordnance Survey® OS Net permanent GPS network. It is not possible to say at this time what quality level these services may be, but given the density of OS Net stations, horizontal accuracy is likely to be from 30 cm to 1 m depending on end-user equipment (much better than any free or commercial service that is currently available in Great Britain).

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 less 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

A European operated Global Navigation Satellite System. See http://www.esa.int/esaNA/galileo.html. Services due to start in 2008. Galileo and GPS combined will lead to improvements in position quality, even in very harsh environments.

GLONASS

Global'naya Navigatsionnaya Sputnikovaya Sistema - Russian GNSS similar to GPS (USA) and Galileo (Europe). 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 10-20 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) GPS receiver. The user’s position is sent to a central control hub where it is improved using Inverse dGPS. A day’s worth of GPS 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.

OSNet^TM

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

RFI

Request for Information - in the context of OSNet, a method of promoting the new service and generating feedback from potential service users and partners.

RFP

Request for Proposal - in the context of OSNet: a method of seeking written proposals for service partnering.

RICS^TM

The Royal Institution of Chartered Surveyors.

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. Requires sophisticated kit (cost usually >£10 000) and more advanced training for the operator. A great part of Ordnance Survey’s large-scale topographic data collection is carried out by RTK GPS. Essential ingredient is an RTK quality signal from an external source.