NTRIP, RTCM, and RINEX: A Complete Guide to GNSS Correction Data Formats for Engineers

NTRIP, RTCM, and RINEX: A Complete Guide to GNSS Correction Data Formats for Engineers

If you work with RTK GNSS for UAVs, autonomous vehicles, or precision surveying, you need to understand three acronyms: NTRIP, RTCM, and RINEX. They are the foundation of how centimeter-accurate positioning gets from a reference station to your moving receiver. This guide explains what each one does, how they work together, and how to configure them on your Eview GNSS receiver.

What Is NTRIP? The Delivery Protocol for Corrections

NTRIP (Networked Transport of RTCM via Internet Protocol) is an HTTP-based protocol that streams GNSS correction data from a server (caster) to one or more clients (rovers). Developed by the German Federal Agency for Cartography and Geodesy, NTRIP has become the universal standard for delivering RTK corrections over IP networks.

How NTRIP works:

• Caster — A server that aggregates RTCM data from reference stations and makes it available on TCP/IP ports (commonly 2101)
• Mountpoint — Each correction stream has a unique mountpoint name (e.g., “VRS_NET” or “RTK_CMR”) that identifies the data format and reference station
• Client — Your GNSS receiver or software connects to the caster, authenticates, and begins receiving the stream
• Authentication — Most public and commercial NTRIP services require a username and password, transmitted as HTTP Basic Auth

NTRIP comes in three versions:

• NTRIPv1 — Original, simple HTTP GET requests. No metadata about available streams until connection.
• NTRIPv2 — Adds sourcetable (list of available mountpoints with metadata), stream selection, and more robust reconnection handling.
• NTRIPv3 — Latest version with revmount (redundant mountpoints), enhanced sourcetable with quality metrics, and improved error reporting. Supported by newer receivers and casters.

RTCM: The Correction Data Language

RTCM (Radio Technical Commission for Maritime Services) is the data format that carries the actual correction information. Developed by the RTCM Special Committee 104, RTCM 3.x is the current standard for differential GNSS corrections.

Common RTCM 3.x message types:

For RTK operation, your rover needs at minimum: a reference station position message (1005/1006), GPS MSM (1074+), and the corresponding satellite ephemeris messages. For multi-constellation RTK, you need MSM for each constellation you track.

RINEX: The Recording Format for Post-Processing

RINEX (Receiver Independent Exchange Format) is the standard file format for storing GNSS observation data. Unlike RTCM which is a stream format, RINEX is a file format designed for post-processing, archiving, and data exchange between different receiver brands.

RINEX file types:

• Observation file (.obs/.rnx) — Contains raw measurements: pseudorange, carrier phase, Doppler, SNR for each tracked signal
• Navigation file (.nav/.gnav) — Contains satellite ephemeris data for position calculation
• Meteorological file (.met) — Optional weather data for atmospheric modeling
• Clock file (.clk) — Satellite and receiver clock corrections

RINEX versions: RINEX 2.11 is still widely supported but limited to single-frequency observations. RINEX 3.04 adds multi-constellation multi-frequency support along with signal strength and quality indicators. RINEX 4.00 (the latest) introduces improved metadata, compact formats, and better support for modern signals like Galileo E6 and BeiDou B2a/B1C.

Septentrio mosaic receivers log RINEX 3.04 and 4.00 natively, making them ideal for PPK workflows where you collect raw data in the field and post-process against a base station for sub-centimeter accuracy.

How They Work Together: A Typical RTK Workflow

Here is how NTRIP, RTCM, and RINEX fit into a real-world RTK GNSS workflow:

1. Reference station (or CORS network) generates corrections in RTCM 3.x format
2. NTRIP caster streams these RTCM messages over the internet
3. Rover receiver (e.g., Eview GNSS Receiver Box with mosaic-X5) connects as NTRIP client, authenticates, and receives the stream
4. Receiver applies corrections in real time, outputting RTK-fixed positions via NMEA or UBX
5. Simultaneously, the receiver logs raw observations in RINEX format to internal storage or SD card
6. Later, RINEX files from rover and base station are post-processed (PPK) for the highest possible accuracy

This dual approach — real-time RTK via NTRIP + RTCM, plus post-processing via RINEX — gives you both operational efficiency and a fallback if the correction link drops mid-mission.

Configuring NTRIP on Eview GNSS Receivers

Eview Septentrio-powered GNSS receivers come with NTRIP client support pre-configured. Here is how to set it up:

Via Septentrio RxControl:

1. Connect to the receiver via USB or Ethernet
2. Open RxControl and navigate to Correction Input → NTRIP
3. Enter the caster IP/URL, port (default 2101), mountpoint, username, and password
4. Set update rate (1 Hz for most applications, 5 Hz for high-dynamics UAV work)
5. Enable automatic reconnection if the link drops
6. Verify status: check that the receiver displays “RTK Float” or “RTK Fixed”

Via SBF commands (for embedded integration):

# Set NTRIP caster
snt, Ethernet1, caster.example.com, 2101, MyMountpoint, username, password, 1

# Verify connection
jps, ReceiverStatus

# Check RTK status
jps, PVTCartesian

Galileo HAS (no NTRIP needed): If you are within Galileo HAS coverage, the mosaic-X5 can receive free PPP corrections directly via satellite L-band broadcast — no NTRIP caster, no cellular data, no subscription. Enable it with the SBF command has, On.

How to Choose Between NTRIP and Satellite PPP Corrections

Not all correction delivery methods are equal. Here is how NTRIP and satellite-based PPP (including Galileo HAS and Trimble RTX) compare:

For most professional applications, a hybrid approach works best: use NTRIP for real-time RTK positioning, and enable RINEX logging as a backup for post-processing if the correction link drops.

Frequently Asked Questions

What is NTRIP and how does it work?
NTRIP (Networked Transport of RTCM via Internet Protocol) streams GNSS correction data over HTTP from a caster server to rover receivers. It is the standard way to deliver RTK corrections without a dedicated radio link.

What is the difference between RTCM and RINEX?
RTCM is a real-time streaming format for live corrections during operation. RINEX is a file format for recording raw observations for post-processing. RTCM = live audio, RINEX = recorded file.

What RTCM message types does a rover need for RTK?
At minimum: reference station position (1005/1006), GPS MSM (1074+), GLONASS MSM (1084+), and corresponding ephemeris messages. For multi-constellation, add Galileo (1094+) and BeiDou (1124+) MSM.

Can Septentrio mosaic-X5 receive NTRIP corrections?
Yes. Mosaic-X5 and mosaic-G5 P3H support NTRIP client mode natively. Eview receiver boxes come pre-configured for NTRIP connectivity.

What is RINEX logging used for?
RINEX records raw GNSS data for post-processing (PPK), base station archiving, satellite modeling, and performance analysis. Septentrio receivers log RINEX 3.04/4.00 natively.

What correction service should I use with Eview GNSS receivers?
Eview receivers work with all major services: public CORS networks, Trimble RTX, PointPerfect, Hexagon SmartNet, and Galileo HAS (free satellite-based PPP corrections).

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