> For the complete documentation index, see [llms.txt](https://docs.rtkdata.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.rtkdata.com/integration-hub/ntrip-clients-and-field-software/ntrip-and-gga-essentials.md). # NTRIP & GGA Explained: AUTO Mountpoint How NTRIP and NMEA GGA work with RTKdata. The caster reads your GGA position to pick the nearest base station via the AUTO mountpoint, not a VRS. Port 2101. This page explains how the NTRIP protocol works, why your device must send GGA messages, and how the AUTO mountpoint routes corrections to you. {% hint style="info" %} Don't have an RTKdata.com account yet? 👉 [Start 30-day Free Trial](https://rtkdata.com/try-rtk-corrections-free-for-30-days/) or [View Pricing](https://rtkdata.com/pricing/) {% endhint %} *** ## 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`, and `aus.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,,*47 ``` When your device connects to the RTKdata caster and requests the `AUTO` mountpoint, the caster needs to know **where you are** so it can: 1. **Select the nearest base station** and stream corrections from it. 2. 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: 1. The caster authenticates the client -- login succeeds. 2. The caster waits for the client's position to assign a base station. 3. No position arrives. The caster continues waiting. 4. 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. | App / Device | Setting Location | | --------------------------------------------------------------------------------------------- | ---------------------------------------------------------------------------------------------- | | [Emlid Flow](/integration-hub/ntrip-clients-and-field-software/emlid-flow.md) | Correction input > NTRIP > **Send receiver position (NMEA)** = ON | | [SW Maps](/integration-hub/ntrip-clients-and-field-software/sw-maps.md) | NTRIP settings > **Send NMEA GGA to caster** = ON | | [u-center (u-blox)](/integration-hub/ntrip-clients-and-field-software/u-center-u-blox-f9.md) | Receiver > NTRIP Client (uses current position automatically; ensure receiver has a valid fix) | | [Septentrio RxTools](/integration-hub/ntrip-clients-and-field-software/septentrio-rxtools.md) | RxControl > Output Settings > NMEA > **GGA @ 1 s**; DataLink forwards it | | [EOS Tools Pro](/integration-hub/ntrip-clients-and-field-software/eos-tools-pro.md) | NTRIP/Differential > **Send NMEA GGA to caster** = ON | | [DJI Pilot / Pilot 2](/integration-hub/ntrip-clients-and-field-software/dji-pilot-pilot-2.md) | 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`: 1. Your device sends a GGA message with its approximate position. 2. The caster looks up the nearest reference station from its network of 20,000+ stations. 3. The caster begins streaming RTCM3 corrections from that station. 4. 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 reference-frame variants `AUTO_WGS84`, `AUTO_ITRF2020` and `AUTO_ITRF2014` work the same way, but deliver corrections in that specific reference frame instead of the regional datum. Stay on `AUTO` unless your project requires a particular frame. Mountpoint names are case-sensitive and must be entered in ALL CAPS, and a local CRS name is not a mountpoint: typing one into the mountpoint field results in no corrections. See [Network & Mountpoints](/get-started/network.md) for details on when a specific frame is worth selecting. *** ## Correction format RTKdata streams **RTCM 3.2** using **MSM messages**, specifically **MSM4 and MSM7**. Any receiver from roughly the last decade decodes both, which is why almost every device connects without a format setting. Two situations are worth knowing about: * **Receivers that only accept legacy RTCM messages** (types 1004 and 1012 rather than MSM) are not compatible. This affects a small number of older instruments. If your receiver documentation lists only legacy message types, contact with the model before you buy. * **Receivers or apps that require one specific MSM type** should be checked once against your working area rather than assumed. If a device connects, receives data and still reports an unsupported or invalid correction format, that is a message-type mismatch, not a credentials or coverage problem. Send us the receiver model and we will confirm. Proprietary formats are never served: **CMR, CMR+, CMRx** (Trimble) and **RTCM 2.3** are not available. If your field software offers these, select RTCM 3.x instead. Leaving a Survey Style on CMRx is one of the most common reasons corrections appear to connect but never produce a fix. *** ## RTKdata Connection Settings | Setting | Value | | -------------- | --------------------------------------------------------------------------------------------- | | **Host** | `eu.rtkdata.com` / `rtk.rtkdata.com` / `aus.rtkdata.com` | | **Port** | `2101` | | **Mountpoint** | `AUTO` (ALL CAPS, case-sensitive) | | **Username** | From [RTKdata Dashboard](https://rtkdata.com/my-account/rtk-credentials/) (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](/get-started/understanding-heights.md). ## Related Guides * [RTK Quick Start Guide](/get-started/quick-start.md): the fastest path from credentials to a first RTK FIX * [NTRIP Server Settings](/get-started/network.md): hosts, port 2101, and when to pick a reference-frame mountpoint instead of `AUTO` * [Fix NTRIP Connection Issues](/support/common-connection-issues.md): what to check when you authenticate but no corrections arrive * [SW Maps](/integration-hub/ntrip-clients-and-field-software/sw-maps.md): a free Android client that makes the GGA toggle easy to test in the field * [NTRIP Clients & Field Software](/integration-hub/ntrip-clients-and-field-software.md): full list of apps and field software with RTKdata setup guides ## Related Industry Solutions * [Surveying](https://rtkdata.com/surveying/) * [Construction](https://rtkdata.com/construction/) * [Agriculture](https://rtkdata.com/agriculture/) --- # Agent Instructions This documentation is published with GitBook. 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