Common Terms

In the general topic areas of GNSS (with or without differential corrections), and in the area of Intelligent transportation systems (ITS) we have a long and perhaps regrettable tradition of making up a new acronym/term each and every time a committee meets.    Here is a short, and very incomplete, cheat sheet of common terms found on the realm of differential corrections those new to this topic area:

General Terms

Base Station = A GNSS device at a known and (typically) fixed location that provide it’s measurement to others (typically using NTRIP) to allow them to process that data and remove common mode errors.  Both DGPS and RTK navigation filters do this but in different ways using different RTCM messages.

DGPS = Differential GPS, a GNSS system using corrections to improve its accuracy.  The term can refer to any type of correction, or can mean a specific type depending on the context in which it is used.  It often can mean a code corrections only (in which case accuracy is limited to 1~2 decimeters), whereas code/carrier corrections (RTK) implies an accuracy of <2cm.

DSRC  = Dedicated Short Range Communications, a 5.8/9Ghz 802.11-like radio channel, sending the SAE J2735 message which in turn contains the RTCM SC104 messages.  The radio specification is defined by IEEE 1609. The SNIP Caster is unique in it’s ability to send this data, learn more here.

GNSS  = Global Navigation Satellite System, the preferred term for the different types of GPS these days (GPS, GLONASS, Galileo, Compass, QZSS, etc.).

GPS = Global Positioning System, the name for the US based GNSS system.

ITS   = Intelligent Transportation Systems.  While a wide range of systems and devices use this term, here we are most often focused on the Vehicle-to-Vehicle exchanges of position vectors at 10Hz, corrected by the flow of Vehicle-to-Infrastructure (the road side) correction messages.  Need to do this? Use-SNIP.

NTRIP  = Networked Transport of RTCM via IP, a common means to send Differential message to devices.  SNIP is an NTRIP Caster.

Rover = The common tern for any deployed GNSS device in the field.  When a rover connect to a Base Station by why of an NTRIP Caster such as SNIP, it is referred to as an NTRIP Client.

RTCM  = A maritime standards organization whose special committee 104 (SC104) sets all the various differential corrections message standards.

RTK  = Real Time Kinematic, a type of GNSS filter using differential corrections to obtain 100x better accuracy, typically ~2cm or so.

RTKLIB  = A popular open source GNSS toolkit used by hobbyists and professionals alike.

SAE   = Society of Automotive Engineers, the standards organization which sets the DSRC message set specification, this is the set of messages sent between Intelligent vehicles. Their DSRC message set wraps the RTCM message inside  of it to securely transport these message to vehicles.

SCSC  = SubCarrier Systems Corp.  A bunch of nice guys who never have ad as much time to update their web pages as they would like.

SNIP  = The term we use for our NTRIP product, formally called simple NTRIP, or sNTRIP.
SNIP® is a registered trademark of SCSC.

SV = Space Vehicle, the common term for a satellite (the SVs and the Ground Control Segment make up the “rest” of a GNSS system beyond the GNSS rover device).


A few Terms used with Virtual Reference Stations

Users often have questions about the different types of Virtual Reference Station mount points that are offered.  The Caster operator is your best source of reference but here are a few basic terminology hints. These terms are often used as part of a mountPt name.

DGPS  = In this content this term implies that the older RTCM2.x message are being send in the stream, and further these are most likely  to be types 18 and19.  And not types 1 or 9 (even if the caster table incorrectly indicates that 1 and 9 are being sent – as many do).

FKP = A network based solution with of code and carrier using a system of gradient messages to describe the overall corrections environment (rather then corrections develop and suited to a unique position). It is in contrast to the MAC approach and has its own message types defined in RTCM.

iMAX = A Leica term for their iMAX network which uses a nearest physical reference station approach with various network correction adjustments.

MAC  = A network based solution with of code and carrier using “Master – Axillary” methods (and messages) as defined in RTCM.

NEAR = Implies that the users NMEA sentence will be used to select the closest physical base station and the user will be connected to that.

NRT = Another term for NEAR

VRS = Virtual Reference Station,  what it means is subject to debate, often involving the above terms.  Of importance to many is that it may not be “virtual” at all if the term is taken to mean creating some sort of non physical reference station that is synthesized between a network of physical stations. That is of course also done, with several benefits, but use of this term does not assure you that this is so.  Nor is a virtual approach of any greater value that a suitable single baseline corrections stream but we digress.

See Also this Page

Here is an article on the general Concepts of NTRIP.

A very terse summary of RTK, NTRIP, and RTCM and how the work together.

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