In this article we explain the key terms used in Precision GPS and what each entails.

RTK – Real Time Kinematic processing

A method to compare the positional estimate of one mobile device (the rover) and another device (the base station). This removes common errors and arrives at a positional accuracy of ~2 centimeters or better.  The method itself (often called a double difference) need not concern us, but depends on the near real time availability of a corrections data stream from a nearby base station.

NTRIP –  Networked Transport of RTCM via Internet Protocol

What a mouthful, and just like it says. NTRIP is a simple protocol to transport RTCM messages over the public internet.  There are three key parts [the Caster, the Clients, and the bases (called Servers)].  And together they allow an individual GNSS device to request and obtain correction services (messages) from a base station. Thousands of networks of NTRIP Casters (like SNIP) are deployed all over the world to provide access to hundreds of thousands of regional/local base stations for this purpose.

RTCM – Radio Technical Commission for Maritime Services

This is the standards body that develops industry wide standardized messages used for all of this. While RTCM develops many other messages and standards for general maritime use, it is the work of Special Committee 104 (SC104) on Differential GNSS Services that we need to know about here.  This is the committee that is charged with developing all the core messages used for precision GNSS. The popular “RTCM3 corrections messages” (the actual title is: Differential GNSS (Global Navigation Satellite Systems) Service – Version 3), is developed by this committee.  The NTRIP protocol is also developed by this committee.

Precision GPS

Any GNSS / GPS methodology that uses additional (external) data beyond simply the raw signals broadcast from GNSS satellites to increase accuracy.  Using RTK is far and away the most common method to use (and NTRIP is the most common method to deliver the needed data).  Other methods such as Precise Point Positioning (PPP) also exist (and also use NTRIP as the delivery method).  All of these methods use RTCM as the preferred message format.

In summary: To do RTK positioning with your GNSS rover device, you need RTCM messages with connections from a nearby base station, typically delivered to your device by way of an NTRIP Caster over a wireless cellular network and the public internet to your GNSS device.

This knowledge base contains over 300 articles on how to setup and operate the SNIP NTRIP Caster.

You might want to start with the FAQ page, Please see:  Frequently Asked Questions

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Need to really know about NTRIP or RTCM details in greater depth?
Download the various RTCM specs themselves,  see this link.