What GGA is
GGA stands for Global Positioning System Fix Data. It is one of several standardised NMEA 0183 sentences — short text strings that GPS and GNSS receivers use to report position and status information. You have probably seen NMEA sentences if you have ever looked at raw receiver output: they begin with a dollar sign and are comma-separated.
In the context of NTRIP, GGA has a specific role: it is the sentence your device sends to the server — in the opposite direction from the correction data — to tell the server where you are. This is unusual because most NTRIP communication is one-way (server to rover), but VRS requires this two-way exchange.
GGA does not need to be accurate to centimetre level for NTRIP to work correctly. A Single or Float solution position — accurate to a few metres — is more than sufficient. The server only needs to know which part of the network you are in, not your exact position.
What a GGA sentence contains
A typical GGA sentence looks like this. Each comma-separated field carries a specific piece of information:
| Field | Meaning |
|---|---|
123519 | UTC time — 12:35:19 |
5230.000,N | Latitude — 52° 30.000' North (Netherlands) |
00452.000,E | Longitude — 4° 52.000' East |
4 | Fix quality — 4 = RTK Fixed (see table below) |
09 | Number of satellites in use |
0.9 | HDOP — horizontal dilution of precision |
25.4,M | Altitude above mean sea level in metres |
Fix quality values
The fix quality field in GGA tells the NTRIP server — and any other system reading the output — what kind of position solution your receiver currently has:
| Value | Meaning | Typical accuracy | Suitable for VRS? |
|---|---|---|---|
0 | No fix | — | No — position is invalid |
1 | GPS fix (Single) | 2–5 m | Yes — good enough to locate in network |
2 | DGPS fix | 0.5–2 m | Yes |
4 | RTK Fixed | 1–3 cm | Yes — best quality GGA |
5 | RTK Float | 0.1–1 m | Yes |
6 | Dead reckoning | Variable | Depends on accuracy |
You do not need Fix before sending GGA
A common misunderstanding is that GGA only works when you already have RTK Fix. In fact, a Single solution (quality 1) is perfectly sufficient. Send GGA as soon as your receiver has any valid position — this allows VRS to start generating corrections, which then helps you get Fix.
How GGA enables VRS
Your receiver gets a rough position
Within 30–60 seconds of powering on outdoors, your receiver acquires satellite signals and computes a Single solution — typically accurate to 2–5 metres. This is enough.
Your NTRIP client sends GGA to the server
Your client connects to the VRS mountpoint and immediately sends the GGA sentence containing your rough position. Most clients send GGA once on connection and then again every 10–60 seconds to account for movement.
The server identifies your location in the network
The VRS server reads the latitude and longitude from your GGA sentence and determines which surrounding physical reference stations apply to your area. This computation takes less than a second.
A virtual station is generated near you
The server synthesises an RTCM3 correction stream as if a base station existed 1–2 km from your position. It starts streaming this data back to your client immediately.
Your receiver achieves RTK Fixed
With local-quality corrections flowing, your receiver resolves carrier phase ambiguities and reaches Fixed — typically within 10–60 seconds in good sky conditions.
When GGA is required vs optional
GGA required — VRS mountpoints
Any mountpoint labelled VRS, MAC or a similar network correction type. The server cannot generate a virtual station without your position.
GGA required — nearest-station auto-selection
Some NTRIP services select the closest physical station automatically based on your GGA position, rather than requiring you to choose a mountpoint manually.
GGA optional — standard single-station mountpoints
When connecting to a fixed mountpoint like RTCM3_NL, the server streams corrections regardless of whether GGA is sent. You can enable GGA for logging purposes but it is not used.
GGA optional — own base station setups
When using your own base-rover configuration without NTRIP, GGA is not involved in the correction exchange at all.
How to enable GGA on your device
The setting name varies between NTRIP clients, but the function is the same on all of them.
In Correction input → NTRIP, select your VRS mountpoint and enable Send GGA to caster. Connect after the receiver has a valid Single solution.
GGA troubleshooting
Connected to VRS but 0 bytes per second
The connection is established but no corrections are flowing. This almost always means GGA is not being sent — or is being sent with quality 0 (no fix). Enable GGA, ensure the receiver has at least a Single solution, then reconnect.
GGA sent but Fix is very slow
If corrections are flowing but Fix takes many minutes, the GGA position may have had low quality at connection time. Disconnect, wait for a better Single solution outdoors, then reconnect.
Moving between areas — does GGA update?
Most NTRIP clients send GGA periodically — every 5–60 seconds. The server receives updated positions and adjusts the virtual station to follow you. You do not need to reconnect when moving around the network coverage area.
Privacy note
GGA contains only your approximate position, altitude, satellite count and fix quality. It contains no personal identifiers; the NTRIP server uses it only to route corrections.
