Let’s be real: there is nothing more convenient than having an NTRIP subscription, which at XRS Geomatics we happily use Premium Positioning. However, in some environments NTRIP doesn't work due to a lack of phone signal or internet connectivity, or when we simply don’t have such a subscription.
The good news is there is still a way to get the OS coordinates (OSGB36 National Grid & Ordnance Datum Newlyn) that you need for your project and the best of all is that the process is free of cost. Whether you need the OS coordinates to set up a base station, record ground control points, or simply to orient your topographic or measured building survey, there is still a way, and this is by performing a PPK (Post-Process Kinematic) using an Emlid GNSS receiver and the open OS Net RINEX Data.
The open OS Net RINEX data is released at a 30-second epoch rate, and we will find it in hourly files. For this reason we recommend taking readings with the GNSS receiver for at least 30 minutes for accuracy—the longer, the better.
Getting Started with an Emlid GNSS Receiver
To start, we will place the Emlid GNSS receiver where we want the OS coordinates, ideally mounted on a pole with a bipod or tripod to keep it in place. In the Emlid Flow app, we will go to 'Logging' and select 'Start Recording.' As we mentioned, we will keep this recording for at least 30 minutes.
Once we stopped recording, we will download the data from the "Recorded Logs and Settings." This will be a ZIP file that includes the UBX file we are interested in.
Obtaining the OS Net RINEX Data
The open OS Net RINEX data is uploaded every 2 hours. After this time has passed, we go to https://www.ordnancesurvey.co.uk/gps/os-net-rinex-data/.
In order to find the nearest OS Net base station, we will enter the location, date, and time from where and when we recorded data with the Emlid GNSS receiver.
Another page will show you where we can download the file, which will be a ZIP containing the RINEX file we need.
Using Emlid Studio for PPK
Now that we have all the files, we open Emlid Studio. If you don’t have it, you can download it here.
We will select 'Static processing,' then drag the UBX file to 'Static Receiver' and the RINEX file to 'Base.' We will include the antenna height of the Emlid GNSS receiver at the time the data was collected. Then, we press 'Process.' We want this to be a 'FIX' for as much of the processing as possible.
If you encounter any difficulties obtaining a stable 'FIX,' consider adjusting the Elevation mask in the settings. We recommend setting it within the range of 25 to 35.
If the outcome is successful, the coordinates will be provided in the ETRS89 reference system.
Converting Coordinates to OSGB36
To transform these coordinates to OSGB National Grid & Ordnance Datum Newlyn, we will use this page: https://www.ordnancesurvey.co.uk/gps/transformation/
Under the ETRS89 tab, we will select Decimal Degrees and paste the coordinates.
Voilà! The OS coordinates we need will appear on the right.
I hope you find this information useful.
Happy Surveying!
Additional notes:
Reference Systems: Emlid GNSS and Emlid Studio default to the WGS84 reference system. However, Emlid Studio automatically adjusts to ETRS89 when using OS Net RINEX Data.
Other GNSS Receivers: You can perform this PPK with different GNSS receivers, but you will need to convert their native file format to RINEX. For example, Trimble files can be converted using this particular software.
Higher resolution OS Net RINEX Data: You have the option to purchase OS Net RINEX Data with shorter epoch rate by reaching out to the Ordnance Survey directly.