Overview of OS Net

OS Net is the infrastructure for realising our national coordinate systems in Great Britain.

The national coordinate systems we use are ETRS89, OSGB36 National Grid, and Ordnance Datum Newlyn (ODN):

• ETRS89 is the standard coordinate system for precise GNSS positioning throughout Europe and is a precise version of the GPS coordinate system WGS84.
• OSGB36 National Grid is the national standard coordinate system for topographic mapping, including all OS mapping.
• ODN is the national standard coordinate system for measuring height above mean sea level. ODN is the usual definition of mean sea level in mapping and engineering in mainland Great Britain. Outlying islands such as Shetland, Outer Hebrides, Orkney, Isle of Man and the Scilly Isles have their own versions of ODN.

OS Net makes the accurate determination of these national standard coordinates much easier and more efficient for land surveyors, compared to traditional (pre-GNSS) surveying methods. It is now possible to determine precise ETRS89 coordinates for your GNSS control stations with a single GNSS receiver, without ever leaving the survey site.

These coordinates can be instantly and precisely transformed to OSGB36, National Grid and ODN height coordinates. Therefore, a greater range of mapping, engineering and environmental projects can now use precise national coordinates than was ever possible before.

By downloading data from the OS Net Global Navigation Satellite System (GNSS) network, and processing this with your own GNSS data, you can obtain precise ETRS89 coordinates of your GNSS survey stations.

The OS Net network consists of about 115 permanently installed geodetic GNSS receivers throughout Great Britain, such that most locations are within 75km of at least one OS Net station, and major urban areas are served by several stations.

All OS Net stations record dual-frequency GNSS data 24 hours a day. Every hour RINEX (Receiver INdependent EXchange) format GNSS data from the network is added to OS Net GNSS network RINEX data server for immediate access.

OSTN15 and OSGM15 are our national standard transformations for transforming GNSS coordinates to OSGB36 National Grid coordinates and orthometric (MSL) heights, and vice-versa.

With OS Net data, the OSTN15/OSGM15 transformation standards make it easier for GNSS surveyors to determine precise coordinates in OSGB36 National Grid, without having to occupy traditional GNSS control stations (triangulation stations or levelled bench marks).

OSTN15/OSGM15 transformation models are freely available to software developers for incorporation in your own software.

See our coordinate transformation tool to transform ETRS89 GNSS coordinates to OSGB36 National Grid.

This includes National Grid eastings and northings, and orthometric height (MSL) for mainland Britain is Ordnance Datum Newlyn (ODN).

The coordinate transformer uses the National Grid Transformation OSTN15 and the National Geoid Model OSGM15. These transformations use more than 2.6 million parameters to precisely model the relationship between ETRS89 and OSGB36/ODN throughout Great Britain.

OS Net supercedes the traditional Ordnance Survey (OS) control networks of triangulation stations and levelled bench marks. These traditional control networks are no longer maintained or used by OS.

The traditional systems of OSGB36 and ODN are now accessed via OS Net derived ETRS89 and the OSTN15 transformation and OSGM15 geoid model.

We list the accuracies of OS Net station coordinates and the OSTN15/OSGM15 transformation models.

To obtain the highest accuracy from OS Net data the difference in phase centre offsets between the OS Net antennae and your antenna need to be factored into your GNSS data processing.

You can also find out about the accuracy of our legacy control data, including passive GPS stations, benchmarks and trigs.