NTRIP & GGA Essentials
This page explains how the NTRIP protocol works, why your device must send GGA messages, and how the AUTO mountpoint routes corrections to you.
What Is NTRIP?
NTRIP (Networked Transport of RTCM via Internet Protocol) is the standard protocol for delivering RTK correction data over the internet. It uses a three-part architecture:
NTRIP Server -- a reference (base) station that generates correction data and sends it to the caster.
NTRIP Caster -- a central server that receives corrections from many base stations and distributes them to connected clients. RTKdata operates the caster at
eu.rtkdata.com,rtk.rtkdata.com, andaus.rtkdata.com.NTRIP Client -- your rover, drone, or field app. It connects to the caster, authenticates, and receives the correction stream.
The client connects to the caster over TCP on port 2101, provides a username, password, and mountpoint name, and then receives a continuous stream of RTCM3 correction messages.
What Is GGA and Why Does the Caster Need It?
GGA (Global Positioning System Fix Data) is an NMEA sentence that contains your receiver's approximate position, fix quality, number of satellites, and altitude. It looks like this:
$GPGGA,123519,4807.038,N,01131.000,E,1,08,0.9,545.4,M,47.0,M,,*47When your device connects to the RTKdata caster and requests the AUTO mountpoint, the caster needs to know where you are so it can:
Select the nearest base station and stream corrections from it.
Optimize the corrections for your specific location (reducing baseline distance and improving accuracy).
If the caster never receives a GGA message from your device, it has no way to determine which base station to use. The result: your session connects successfully, but no correction data is delivered. This is the single most common cause of "connected but no corrections" issues.
What Happens When GGA Is Not Sent
When a device connects without sending GGA:
The caster authenticates the client -- login succeeds.
The caster waits for the client's position to assign a base station.
No position arrives. The caster continues waiting.
The client sees 0 kB/s throughput and no corrections.
This appears in RTKdata session logs as a 0 GGA session. If you see "connected but no data" or "waiting for base", the first thing to check is whether GGA output is enabled.
How to Enable GGA
The setting name varies by app, but the concept is the same: your device must send its approximate position back to the caster.
Correction input > NTRIP > Send receiver position (NMEA) = ON
NTRIP settings > Send NMEA GGA to caster = ON
Receiver > NTRIP Client (uses current position automatically; ensure receiver has a valid fix)
RxControl > Output Settings > NMEA > GGA @ 1 s; DataLink forwards it
NTRIP/Differential > Send NMEA GGA to caster = ON
Automatic once the drone has a satellite fix. Must be outdoors.
GGA Rate Recommendation
Set GGA output to 1 Hz (once per second) where your app allows you to configure the interval. This gives the caster an up-to-date position so it can optimize corrections as you move. Some apps default to 5 or 10 seconds, which works but is less responsive if you are covering large distances quickly. A 1 Hz rate uses negligible bandwidth (about 70 bytes per message).
How the AUTO Mountpoint Works
When you connect to mountpoint AUTO:
Your device sends a GGA message with its approximate position.
The caster looks up the nearest reference station from its network of 20,000+ stations.
The caster begins streaming RTCM3 corrections from that station.
As you move and send updated GGA messages, the caster can switch to a closer station if one becomes available.
This means AUTO is a dynamic, location-aware mountpoint. It removes the need to know which specific base station to connect to. For most workflows, AUTO is the recommended choice.
The other mountpoints (AUTO_WGS84, AUTO_ITRF2020, AUTO_ITRF2014) work the same way but deliver corrections in a specific reference frame instead of the regional datum. See Network & Mountpoints for details on when to use each.
RTKdata Connection Settings
Host
eu.rtkdata.com / rtk.rtkdata.com / aus.rtkdata.com
Port
2101
Mountpoint
AUTO (ALL CAPS, case-sensitive)
Username
From RTKdata Dashboard (starts with rtk)
Password
From RTKdata Dashboard
Send GGA
ON (required)
Heights
RTKdata delivers ellipsoidal heights in all reference frames. If you need orthometric (mean sea level) elevations, apply a geoid model in your rover software or during post-processing. See Understanding Heights.
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