Surveying & GNSS

What is NTRIP?

NTRIP — Networked Transport of RTCM via Internet Protocol — is how GNSS correction data gets from a base station to your rover over an ordinary internet connection. It is what lets you run centimeter-accurate RTK using a cellular link instead of a line-of-sight radio.

What
An open protocol for streaming RTCM correction data over the internet (HTTP-based).
Carries
RTCM messages — the standard format for GNSS base-station corrections.
You need
A caster address + port, a mountpoint name, and a username / password.
Result
RTK corrections delivered to your rover anywhere it has a data signal.

The Problem NTRIP Solves

Classic RTK pushes corrections from base to rover over a UHF radio. That works, but it is limited by range, line of sight, and licensing. NTRIP replaces the radio with the internet: the base’s corrections are uploaded to a server on the web, and any rover with a cellular or Wi-Fi connection can pull them — whether it is across the site or across the county.

The data being moved is RTCM (Radio Technical Commission for Maritime Services), the industry-standard message format for GNSS corrections. NTRIP is simply the delivery mechanism; RTCM is the cargo.

The Four Parts

  • NTRIP Server — the software at the base station that uploads its RTCM corrections to the caster. (Confusingly named: the “server” is the data source, not the central hub.)
  • NTRIP Caster — the central internet server that receives streams from one or more bases and hands them out to clients. This is the address you connect to.
  • Mountpoint — a named correction stream on the caster. One caster can host many mountpoints (one per base, or per correction type). You choose which to subscribe to.
  • NTRIP Client — the rover (or its data collector) that logs into the caster, selects a mountpoint, and downloads the correction stream to feed its RTK engine.

Mountpoints and the Source Table

When a client connects, the caster can return a source table — a directory of every available mountpoint with its location, the satellite systems it carries, the RTCM version, and its format. Most data collectors fetch this list automatically so you can simply pick the nearest or most appropriate stream from a menu.

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Pick a base close to you

RTK accuracy degrades with the baseline — the distance between base and rover — because the two stop sharing the same atmospheric errors. Choose the mountpoint nearest your work area, or use a network stream (below) that synthesizes a base right next to you.

Connecting a Rover

To bring up an NTRIP connection you will enter, in your field software:

  • Caster address and port (commonly 2101).
  • Username and password for the service.
  • The mountpoint, usually chosen from the source table the caster returns.

Once connected, the corrections flow continuously and the rover should reach a Fixed solution within seconds. Many services also expect the rover to send its approximate position back up (as a GGA sentence) so a network caster can tailor the correction to where you are.

Single Base vs Network RTK

A mountpoint may be fed by a single physical base station, or by a reference network — a regional grid of permanent stations (a CORS network). Network services model the errors across the whole region and deliver a VRS (Virtual Reference Station): a correction stream that behaves as if there were a base standing right next to your rover, no matter where you roam. That keeps the effective baseline short and accuracy high across a wide area — which is why many surveyors subscribe to a network NTRIP service rather than running their own base.