Free RINEX Post-Processing for UK Surveyors

What is RINEX and Why Is It Free?

Click to enlarge

An OS Net reference station — one of around 110 permanently fixed GNSS receivers across Great Britain that continuously log raw satellite data.

RINEX (Receiver Independent Exchange Format) is the standard file format for raw GNSS satellite observations. When your GNSS rover records signals from GPS, Galileo, GLONASS and other satellites, the raw measurements — distances to each satellite, carrier phase readings, timing data — can be stored in RINEX format.

Ordnance Survey operates a network of around 110 permanently fixed GNSS receivers across Great Britain called OS Net. These stations continuously log raw RINEX data and make it available for free download via the OS Data Hub. Because each station’s exact position has been determined to millimetre accuracy, its RINEX data can be used as a trusted base station for any survey in the area.

Why does Ordnance Survey publish it for free?

• Open data policy — OS follows an open-data model for reference station observations, supporting research, education and commercial applications
• Post-processing flexibility — not everyone has real-time internet coverage in the field; RINEX makes high accuracy achievable offline
• Scientific uses — researchers, universities and meteorologists use it for ionosphere modelling, ground subsidence monitoring and timing work
• Verification and quality control — surveyors can re-process completed jobs using the archived data

RTCM vs RINEX — When to Use Which

Click to enlarge

RTCM streams corrections in real time via NTRIP; RINEX is downloaded after the survey and processed on your computer.

RTCM (Radio Technical Commission for Maritime Services) is the format used for real-time corrections. These are streamed live to your rover via the internet using a protocol called NTRIP — typically from OS Net or a commercial provider. You see corrected centimetre-level positions immediately in the field.

RINEX with PPK (Post-Processed Kinematic) takes a different approach: you log raw data during the survey, then download matching base station RINEX afterwards and re-process everything on your computer.

Both methods routinely achieve 1–3 cm horizontal accuracy under good conditions. The choice depends on your situation:

The Free Workflow — Step by Step

This is the complete workflow from field to corrected coordinates using only free tools and data. It works with any low-cost rover that can log raw GNSS data — including the DATAGNSS Nano used with SW Maps.

1. 1

   Enable raw data logging on your rover

   In SW Maps, go to GNSS Settings and enable raw data logging in UBX format. Set the logging interval to 1 second (1 Hz). Start logging a few minutes before your survey begins and keep it running a few minutes after — the overlap helps the processing software initialise.

   You can still connect to a live NTRIP/RTK server at the same time. The app records both real-time corrected positions and the raw UBX data simultaneously.

2. 2

   Complete your survey and note the time window

   Carry out your survey as normal. Note the approximate start and end times (or use the file timestamps). You will need these to download the matching OS Net RINEX file.

3. 3

   Download the matching OS Net RINEX file

   Go to the OS Data Hub RINEX page (free account required). Select the OS Net station nearest to your survey area (ideally within 20–50 km), choose your date and time window, and download the RINEX observation file (.rnx or .obs).

   Files are typically available in hourly chunks. Data is retained for at least 45 days; longer archives are available via the BIGF archive at the University of Nottingham.

4. 4

   Load both files into Emlid Studio (or RTKLIB)

   Open Emlid Studio and go to the PPK tab. Load your rover’s UBX file as the Rover input and the OS Net RINEX file as the Base input. Emlid Studio will convert the UBX to RINEX automatically if needed. Set the correct antenna height for your rover setup.

   For RTKLIB: use RTKCONV to convert the UBX file to RINEX first, then use RTKPOST with the same inputs.

5. 5

   Run PPK and export your corrected coordinates

   Click Process. The software resolves carrier phase ambiguities and applies forward and backward smoothing to your data. The output is a new, corrected coordinate file in your choice of format — CSV, KML, GeoJSON or POS. Import this into QGIS, Google Earth, SW Maps or any GIS tool to view your corrected survey on a map.

Free Tools: Emlid Studio vs RTKLIB

Click to enlarge

Emlid Studio’s PPK interface — drag in your rover UBX file and OS Net RINEX file, then click Process.

Two free tools cover the needs of most UK surveyors at every skill level:

Getting OS Net RINEX Data — Free via the OS Data Hub

Click to enlarge

The OS Data Hub RINEX page — select a station near your survey area, choose your date and time window, and download for free.

The OS Data Hub RINEX service gives free access to raw observation files from around 110 OS Net stations covering all of Great Britain.

How to download

1. Create a free account at osdatahub.os.uk
2. Go to Downloads → Open Data → RINEX
3. Use the map to find the OS Net station nearest to your survey area
4. Select the date and the one-hour block (or multiple blocks) covering your survey time
5. Download — files are typically 5–15 MB compressed per hour

Which station to choose

Select the OS Net station closest to your survey area. For most UK locations, there will be a station within 20–40 km. Accuracy is best within 50 km; beyond 100 km the baseline becomes longer and results can degrade slightly, though network processing modes in RTKLIB can extend this range.

No Internet Needed in the Field

One of the most practical advantages of the PPK / RINEX approach — especially for rural boundary surveys in England and Wales — is that you do not need a mobile data connection at all during the survey.

This makes RINEX post-processing ideal for:

• Rural properties with poor mobile coverage
• Woodland surveys where signal is intermittent
• Hobbyist or semi-retired surveyors who want to keep costs to zero
• Anyone who collected raw data but did not have a live RTK connection at the time

What Files Do You Get After Processing?

Click to enlarge

Corrected GPS survey points displayed in QGIS after PPK post-processing — ready for mapping, reporting or further GIS analysis.

After running PPK in Emlid Studio or RTKLIB you will have one or more output files containing your corrected coordinates. Common formats include:

These outputs can be loaded back into SW Maps, OsmAnd or any GIS platform to view your corrected survey on a map. They are also compatible with the .dxf, .geojson and .csv export files available for BoundaryFinder GPS boundary reports.