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Improving GPS in Europe

EGNOS Architecture
EGNOS Architecture

GPS-booster EGNOS’ signal is free and its accuracy compliance area covers most of Europe.

Maps are ubiquitously used nowadays, starting from civilian applications to georeferencing of items for businesses and administrative bodies. Maps are needed for managing natural resources, viewing inventories or stocks, locating interesting places, organizing logistics, and seeing business or any other data in a geographic context. Underlying all those applications there is a common need — objects need to be positioned.

European Geostationary Navigation Overlay Service (EGNOS) can help to locate great amount of points with sub-meter accuracy in an easy, affordable and flexible way and in real time. It can boost the data capture, usually the most time-consuming process in the development of a mapping or GIS application.

How does EGNOS work?

EGNOS is Europe’s first concrete venture into satellite navigation. Essentially a ‘pre-Galileo’ system, EGNOS uses geostationary satellites and a network of ground stations to receive, analyze and augment GPS, and in the next version Galileo signals.

EGNOS
EGNOS 95% error ellipse Feb. 1, 2016

It augments the L1 (1575.42 MHz) Coarse/Acquisition (C/A) GPS civilian signal by providing corrections and integrity information for safety of life applications. EGNOS includes a network of 39 reference stations in more than 20 countries. These reference stations pick up signals from GPS satellites, which are afterwards processed in Mission Control Centres, so that satellite clocks, satellite position and ionospheric effects are corrected. EGNOS messages are broadcast through two geostationary satellites and through Internet via the EDAS Service.

The EGNOS signal is free and its accuracy compliance area covers most of Europe. There are different means for users to access EGNOS corrections:

  • EGNOS Signal in Space, directly via the geostationary EGNOS satellites (same L1 frequency as GPS satellites) using a GPS receiver that is EGNOS-enabled, without any additional cost.
  • Via EDAS (EGNOS Data Access Service), through the Internet in real time or in form of archive data by the EDAS FTP Service.

Satellite-based corrections

EGNOS has been designed and developed with the general goal to improve GPS performances in Europe. Its Open Service is intended to offer these benefits for the users of general-purpose applications without any charge and does not require specific authorization.

EGNOS 2DRMS
EGNOS 2DRMS as on Feb. 1, 2016

To receive the satellite EGNOS signal, a SBAS receiver (all the SBAS receivers are EGNOS compatible) is required. The difference with a GPS receiver is the special software which enables the lock onto the EGNOS satellites and applies the EGNOS corrections to the GPS signal. Today, most of the commercial GPS receivers provide EGNOS capability.

In the particular case of mapping, the positional accuracy is defined mainly for horizontal coordinates (although EGNOS provides also corrected vertical position). The following parameters are key factors for users:

  •  The Error Ellipse defines a confidence region for the horizontal coordinates of a point. It is an approximate graphical representation of the standard deviation in two directions (lowest and highest precision directions). The most common confidence level used for error ellipses calculation is 95%.
  •  The 2DRMS represents twice the Distance Root Mean Square. The DRMS is the root mean square of the radial distances from the true position to the observed positions obtained from a number of trials.

EGNOS Open Service accuracy for mapping is homogenous all around Europe and independent from the distance to the EGNOS reference stations.

Advanced positioning techniques

EDAS provides free-of-charge access through Internet to all the data generated and collected by the EGNOS infrastructure for real-time applications and also for post-processing products. Apart from the EGNOS messages, EDAS also transmits Differential GNSS (DGNSS) corrections and Real-Time Kinematic (RTK) messages in order to support high precision positioning when located close to an EGNOS station. Taking into account the proliferation of user applications with stringent accuracy requirements in the surveying domain, the EDAS service can make a difference by enabling the implementation of advanced positioning techniques.

EGNOS Stations
EGNOS Stations & EDAS DGNSS coverage

The positioning techniques supported by EDAS are the following, providing higher accuracy (from sub-meter to centimetre accuracy) than GPS standalone:

  • EGNOS corrections can be applied in real time using the EDAS SISNeT Service through Internet, especially important in areas when the visibility of EGNOS geostationary satellites can be obstructed by high buildings, mountains, or any other obstacle.
  • DGNSS technique can be used in real time through the EDAS NTRIP Service, applying DGNSS corrections from a close EGNOS station (within 500 km baseline). Taking into account that the reference stations have a known location, the errors of the satellite (GPS and GLONASS) measurements received can be accurately computed and broadcast to users in the surroundings of the station.
  • RTK positioning with centimetre level accuracy can be computed using EDAS NTRIP service when located within 40 km from the EGNOS station.

Applications for surveying and mapping

More and more manufacturers are introducing optimized EGNOS implementation for surveying and mapping devices. According to the GSA Market Report 2015, EGNOS-enabled devices for surveying are increasing their market share in Europe and EGNOS capability is expected to be available in more than 80% of GNSS receivers.

Creating spatial data infrastructures, including water delivery or sewer systems, are suitable EGNOS applications for local governments. Energy, telecom and utilities companies, owners or managers of extensive infrastructures may rely on EGNOS surveys that allow them to map infrastructure accurately and cost efficiently. Also, the European National Geographic Institutes can benefit from using EGNOS for the elaboration, georeferencing and control of their cartography. So, EGNOS and EDAS information can be successfully applied to any surveying or mapping application requiring sub-meter accuracy.

Reinhard Blasi
Market Development, GSA

Sofia Cilla
ESSP SAS