Find out more about the standard error distances of the OS Net active and passive networks, and that of the coordinate transformer
The difference in phase centre offsets between the OS Net antennas and your antenna need to be included in your GNSS data processing.
A Global Navigation Satellite System (GNSS) baseline is measured between the phase centres of the two antennas. To relate this baseline to the station markers of the two end points you need to know the vertical height from the station marker to the antenna phase centre.
The phase centre is not a physical point that can be measured, so you need to know the offset of the phase centre from a physical point on the antenna.
Using the correct phase centre offsets becomes very important when different antenna types are used in a survey.
When using OS Net data it is very likely that your antenna will be different from the antennas at the OS Net stations. The difference in phase centre offsets between the OS Net antennas and your antenna need to be included in your GNSS data processing.
The antenna heights of all OS Net stations are measured vertically from the station marker to the Antenna Reference Point (ARP) for each antenna, which is usually the base of the antenna mount.
This height is the one given in the RINEX file header. The offset from the ARP to the phase centre is then added to the ARP height (usually in the processing software) to give the height of the phase centre above the ground marker.
The main phase centre offset component is vertical (up) but there are also small horizontal offsets (north and east) that can be applied. There are actually two phase centres in an antenna – one for the L1 frequency and the other for L2, and each phase centre has a different offset.
In addition to the main offsets there are additional small offsets given as tables of satellite azimuth and elevation dependant corrections. All offsets are usually delivered in the standard ANTEX format.
The offsets used by Ordnance Survey (OS) are the same as those used by the International GNSS Service (IGS) and the EUREF Permanent Network (EPN) at the time of the computation of the OS Net station coordinates.
The full offsets and tables of elevation and azimuth dependent corrections are available to download (in ANTEX format) - download full phase centre offsets (ANTEX format in a ZIP file).
More information on antenna calibration, phase centre offsets and elevation dependent phase centre modelling can be found at the GPS Antenna Calibration page of the US National Geodetic Survey.
Where available, the offsets used by Ordnance Survey (OS) are the same as those used by the International GNSS Service (IGS) and the EUREF Permanent Network (EPN) at the time of the computation of the OS Net station coordinates.
There are sometimes differences between the IGS/EPN offsets and the calibrations from the NGS. It is more important that OS use antenna calibration consistent with IGS/EPN so that OS Net is in the closest possible agreement with other national networks in Europe.
Discover OS Net data, providing Global Navigation Satellite Systems (GNSS, previously referred to as GPS) data.
GNSS data in standard RINEX (v3) format. Hourly files at 30 second rate.