Ordnance Survey – Great Britain's national mapping agency
![Ordnance Survey home page [logo]](/images/gui/logo-os.gif){kind=logo}
The OS Net website offers two key free services that are primarily aimed at professional surveyors, geodesists and GIS developers. Together, these services improve the accessibility of the national coordinate systems in Great Britain, and provide for more efficient ways of working.
There is also an description of the various services, together with a guide to how they can be used by surveyors, case studies and some FAQs.
OS Net comprises over 100 continuously operating GNSS reference stations spread over the whole of Great Britain. You can download precise GPS data from these stations within 90 minutes of the time of observation. By processing this with your own GPS data, you can obtain precise ETRS89 coordinates of your survey stations.
Typical users will have at least one dual-frequency survey grade GPS receiver and post-processing software.
NEWS UPDATE: RINEX data is now available from over 100 Active OS Net stations across Great Britain.
This facility allows you to precisely transform between ETRS89, GPS derived, coordinates and Ordnance Survey National Grid coordinates and heights above mean sea level (Ordnance Datum Newlyn for mainland Britain). Ordnance Survey map coordinates and heights can therefore be derived for any GPS position in Great Britain simply through using a precise transformation. For GI software developers, there is a free precise solution to the GPS/Ordnance Survey coordinate discrepancy problem.
Typical users would be anyone who needs to transform GPS coordinates to National Grid or Ordnance Survey heights or vice versa, for example GIS developers or land surveyors.
These databases allow free access to several frozen control datasets:
Passive GPS station database, you can access full information and coordinates of over 900 precisely positioned Ordnance Survey GPS reference marks across Great Britain.
Vertical control (bench marks), a searchable database of the archive of some 750,000 bench marks
Liverpool - Newlyn datum differences, a searchable database providing the vertical difference between the Liverpool and Newlyn vertical datums for your location
Triangulation stations, a searchable database of the 21,000 OSGB36 horizontal archive control stations