Quick Answer
NTRIP lets your Emlid receiver obtain centimetre-level RTK corrections over a mobile data connection, with no base station required. In the UK, you can get free correction data from the Ordnance Survey OS Net network, giving your Emlid Reach receiver survey-grade accuracy for nothing beyond your mobile data allowance.
What Is NTRIP?
NTRIP (Networked Transport of RTCM via Internet Protocol) is a protocol that streams GNSS correction data from reference stations to a rover over the internet. Instead of setting up your own base station and radio link, your Emlid receiver connects to an NTRIP caster via a mobile data connection and receives real-time correction messages in RTCM format.
For surveyors and engineers working in the UK, NTRIP is often the simplest way to achieve centimetre positioning. The correction source is a network of continuously operating reference stations (CORS) that broadcast their observations online. Your receiver uses these observations to calculate and remove errors in its own position.
Free vs Paid Correction Sources in the UK
OS Net (Free)
The Ordnance Survey operates OS Net, a network of around 100 GNSS reference stations across Great Britain. OS Net provides free RINEX data and NTRIP streams for non-commercial and research use. For many surveyors, this is the primary free correction source available in the UK. You need to register for an account on the Ordnance Survey website to access the NTRIP caster.
Commercial Networks (Paid)
Several commercial providers offer subscription-based NTRIP correction services with wider coverage, lower latency, and guaranteed uptime:
- SmartNet (Leica/Hexagon) — one of the most widely used commercial correction services in the UK, offering coverage across the entire country with subscription plans suited to professional surveyors.
- Trimble VRS Now — provides virtual reference station corrections with broad UK coverage.
- OstNet / other regional providers — smaller networks that may offer competitive pricing for specific areas.
Commercial services typically cost in the range of a few hundred to around a thousand pounds per year, depending on coverage and features.
What You Need
- An Emlid Reach receiver (RS4 Pro, RS3, or RS2)
- A smartphone or tablet running the Emlid Flow app
- A mobile data connection — either a smartphone hotspot or a dedicated 4G/5G router
- A SIM card with an active data plan (NTRIP streams use relatively little data, typically under 50 MB per hour)
- NTRIP credentials from OS Net or a commercial provider
Getting OS Net Credentials
- Visit the Ordnance Survey website and navigate to the OS Net section.
- Register for a free account. You will need to provide your name, organisation, and intended use of the data.
- Once approved, log in to the OS Net NTRIP caster portal.
- Note down your username, password, the NTRIP caster address, and port number.
- Check the available mountpoints and select one near your survey area.
Setting Up NTRIP on Emlid Flow
- Open the Emlid Flow app and connect to your receiver via Bluetooth.
- Tap the gear icon to open receiver settings.
- Under Correction source, select NTRIP.
- Enter the NTRIP caster address, port, username, and password from your OS Net (or commercial provider) account.
- Tap Fetch mountpoints to retrieve the list of available reference stations.
- Select the mountpoint closest to your current location. The closer the station, the better your correction quality.
- Tap Connect. The app should display a connected status and begin streaming corrections.
- Check the status bar — you should see the receiver transition from Single to Float and eventually to Fix mode, indicating centimetre-level accuracy.
For a broader guide on setting up your Emlid equipment, see our article on how to set up Emlid Reach base and rover RTK surveying.
Troubleshooting Common NTRIP Issues
High Latency or Delayed Corrections
If the age of correction climbs above a few seconds, check your mobile signal strength. NTRIP requires a stable data connection. Switching between 4G masts can cause brief dropouts. A dedicated SIM card in a mobile router often performs better than a phone hotspot.
Frequent Dropouts
Dropouts usually stem from network instability. Try moving to an area with better mobile coverage, or use a network provider with stronger rural coverage in your region. Some surveyors carry SIM cards from two different networks as a fallback.
Wrong Mountpoint Selected
Selecting a mountpoint far from your location degrades accuracy. Always choose the nearest reference station. If you move more than 30–40 km during a survey, reconnect to a closer mountpoint. Some commercial networks use virtual reference stations (VRS) that handle this automatically.
Receiver Stays in Float Mode
If your receiver will not achieve a fixed solution, verify the correction stream is active and the mountpoint broadcasts RTCM3 messages compatible with your receiver. Check that you have a clear sky view with minimal obstructions. Poor satellite geometry or heavy tree cover can prevent a fix even with good corrections.