GPS TERMINOLOGY
(or Alphabet Soup)

I just finished doing some research trying to figure out what GPS would best suit my needs. Reading through the specifications is like trying to read a table full of Scrabble tiles. Here are some short explanations on what the various acronyms stand for and a definition of terms related to GPS.

Some of these concepts and terms I understand, others I don't. Also I don't think these definitions have all the meanings detailed. If you find an error, or if you can give me a better definition please let me know.

GPS Terminology including Acronyms

AIS

Automatic Identification Systems. This is required of passenger vessels and large vessels 300 tons or larger. It is a tracking system. Identification and position information is broadcast and if a chartplotter is equipped with appropriate receiving equipment, the position and ID of the sending vessels can be displayed on the Chartplotter. AIS supplements radar information. It can track unique identification, position, course and speed. AIS combines GPS (or LORAN) and VHF radio plus features such as gyrocompass or rate of turn indicator. Goals of AIS is collision avoidance, traffic management in busy areas, Maritime security and control of illegal activity such as smuggling and drug traffic. It also provides information for Search and Rescue and for investigation of Accidents.
Here is a page which Tracks AIS equipped vessels

Anchor Drag Alarm

GPS and Chart plotters sometimes offer a feature which monitors the swing of a boat at anchor. If the position of the boat deviates from it's expected swing around the anchor, an alarm is sounded.

ARPA

Automatic Radar Plotting Aids. Radar information can be connected to some chartplotters and display radar input. A marine radar with automatic radar plotting aid (ARPA) capability can create tracks using radar contacts calculate the ship's course, speed and closest point of approach. Used to aid navigation and avoid collisions.

ASCII

American Standard Code for Information Interchange. A character-encoding scheme based on the English alphabet. ASCII codes has been used to represent text in computers, communications equipment, and other devices that use text. NMEA 0183 uses an ASCII serial communication protocol.

BEIDOU

Chinese regional navigation system. Similar to GPS.

Chart Plotter

This is a device used in ship navigation which shows the boat's real time position on a chart. Chartplotters blend GPS positioning data and chart information. Chartplotters also show heading and speed. Many chartplotters are connected to other devices and sensors to display more information on the charts. Sonar provides depth and bottom contour as well as fishfinding features. Radar information can be integrated in the display, as can AIS automatic information systems. The difference between a GPS unit and a Chartplotter is the chart display. A GPS is a device for giving position. Often GPS will also have a compas feature and a speed and direction capability. A chartplotter can be thought of as a monitor displaying charts, with gps and

Checksum

A calculation that is done to data to verify that it is accurate. This is sometimes used by communication protocols to check that the transmission is complete and not damaged. The checksum is the result of a mathematical operation done on the data. A common occurance of a checksum is in bar code readers where sometimes the last digit is a checksum tester.

CMOS

Complementary Metal-Oxide-Semiconductor is a technology used in the construction of integrated circuits. It is is used in microprocessors, static RAM, microcontrollers, and other digital logic circuits. CMOS is also used for several analog circuits such as image sensors (CMOS sensor), data converters, and highly integrated transceivers for many types of communication equipment.

DSC

Digital Selective Calling is a communication standard for sending pre defined digital messages, using various radio frequency systems. Most commonly in recreational boating is the VHF system. It is a part of GMDSS, the Global Maritime Distress Safety System. Before being able to use DSC capabilities a user must have MMSI number. These are assigned individually upon application. I applied for mine from the Canadian ministry of Transport. It was free.
When sending a distress signal the DSC will broadcast an automatic message including the MMSI number, and if connected to a functioning GPS, the coordinates of the sending vessel. By pressing only one button a message is sent with ID and position. In my VHF radio there is a special DSC button which is covered. I need to remove the cover and press the signal button. Some chart plotters /GPS can broadcast and receive DSC messages when connected to a radio

Dual Beam Sonar/dual frequency

When sonar pulse is emitted the angle is controlled by the frequency of the pulse. A higher frequency (200khz) produces a narrow beam which gives better accuracy but not a big picture whereas a lower frequency (83khz) produces a wider beam which gives good overall information but not as detailed. When a sonar uses dual beam it generates 2 different pulses at different frequencies which together provide a larger view and more accurate information.

ECDIS

Electronic Chart Display and Information System. ECDIS display on a chartplotter can legally be used instead of paper charts. To qualify as an ECDIS chart, the electronic charts have to meet the techical requirements of the (IMO) International Marine Organization and various National hydrographic bodies. Not all charts displayed on chartplotters meet these requirements.

EGNOS

European Geostationary Navigation Overlay Service, is a satellite based augmentation system developed to augment the accuracy of GPS, GLOSNASS and Galileo systems.
It is most effective in the west central area of europe. Similar to WAAS in North America and MSAS in Asia and Japan. These are Satellite Based Augmentation Systems (SBAS)

EMI/RFI

EMI Electromagnetic Interference is also referred to as RFI Radio Frequency Interference. Disturbance that affects an electrical circuit caused by electromagnetic induction or electromagnetic radiation emitted from exernal sources. The interference can come from natural phenomena such as northern lights, or from man made sources. Jamming is a deliberate use of interference.

ENC

Electronic Navigation Chart are charts which can be viewed on electronic equipment. They are usually integrated with a GPS systems to be viewed on Chartplotters. They can be ECDIS compliant or not. If they are they fulfil the legal requirements to carry charts.

Fish finder

Specialized sonar system used by fishermen to locate and identify the size of fish. Fish finders typically also display water depth, temperature and bottom contour. Chart Plotters often have fishfinding functions if they offer sonar.

GMDSS

Global Maritime Distress Safety System

GNSS

Global Navigation Satellite System, is a general term for satellite navigation systems that provide global geo-spatial positioning. GPS, Galileo and GLONASS are all examples.

GPS

Global Positioning System, is a satellite based navigation system. It provides position as long as there is unobstucted line of sight to at least 4 GPS satellites. GPS is maintained by the US Government. Other countries are developing their own systems GLOSNASS is the Russian System, Galileo Positioning System will be the European system and the Chinese are developing the Compas Navigation system. The Indian system is also in the works.
A GPS unit does not show positions on a map. Properly speaking when a GPS shows position on a chart it is a Chart Plotter.
GPS will give you position in longitude and latitude. This information can be passed on to other marine instruments such as DSC (Digital Selective Calling) radios. GPS technology is often integrated in stand alone marine instruments.

GLONASS

Is the Russian Global Navigation Satellite System which became complete sometime around 2005

HD-ID

Garmin's High-definition Identification (HD-IDT) target tracking technology used in their fishfinders.

IHO

International Hydrographic Organization. The Mission of the IHO is to create a global environment in which States provide adequate and timely hydrographic data, products and services and ensure their widest possible use
The IHO is the recognised authority on hydrographic surveying and nautical charting. IHO standards and specifications that are normally used in official communications.

IMO

International Marine Organization set requirements for (ENC) electronic navigation charts, among many other duties.

IRNSS

Indian Global Navigation System soon to be operational

Latitude

The North South position on Earth. 0 degrees is at the equator while 90 degrees is at the poles.

Longitude

The East West position on Earth. By Definition 0 degrees is called the prime meridian and it is located in Greewinch England. Longitude article on Wikipedia

LORAN

LOng RAnge Navigation is a terrestrial (not reliant on satellites) radio navigation system. It utilizes radio signals transmitted by fixed land beacons. Loran is quickly being replaced by GPS. US and Canada has ceased supporting Loran transmissions. Because Loran relies on radio transmission the problems associated with radio applies to it.

Navigation Chart

A map representing a marine or water area and nearby Coastlines. Nautical charts provide information on depth, obstacles, buoys, currents and other data of importance to navigation. When in electronic format then the chart is ENC electronic navigation chart. Electronic Charts may or may not be ECDIS. If they are they can legally replace paper charts in many countries.

MSAS

Multi-functional Satellite Augmentation System, A satellite system designed to improve the accuracy of GPS and other satellite navigation and positioning systems. Serves East Asia and in particularly Japan.
Similar to WAAS in North America and EGNOS in W Europe which are other Satellite Based Augmentation Systems (SBAS).

NMEA

National Marine Electronics Association has defined and controls a combined data and electrical communication specification used between many marine electronic devices. There are 2 versions in common use, NMEA 0183 and the more recent NMEA 2000. NMEA 0183 uses an ASCII serial communication protocol. Read more about NMEA 0183 here. NMEA 2000 is more complex. It has higher data rate, uses a binary message format instead of ASCII. It also allows a multiple-talker, multiple-listener data network. NMEA 0183 functions as a single-talker, multiple-listener (simplex) serial communication protocol. Many devices support both protocols.
NMEA is not restricted to GPS but rather is a specification that any marine electronic instrument can use to communicate information to other devices. GPS, Chart Plotters, Auto Pilots, depth sounders are all examples of devices that could use NMEA if they are so enabled.

RNC

Raster Navigation Charts. Essentially a scan of a paper chart. It is subject to the same limitations as paper projections such as mercator or conic etc. Raster images have limits of zoom. Think about zooming into a jpg photograph. It eventually becomes meaningless squares, this is a raster image.

RoHS

Restriction of Hazardous Substances Directive. The European directive restricts the use of 6 hazardous materials in the manufacture of various electronic and electrical devices. Restricted substances are: Lead, Mercury, Cadmium, Hexavalent Chromium, Polybrominated biphenyls, Polybrominated diphenyl ether.

SAR

Search and Rescue

SOLAS

Surface Ocean Lower Athmosphere Study has a goal of quantifying and understanding the main biogeochemical-physical interactions between Ocean and Athmosphere and how this affects climate and environmental change.

SONAR

SOund Navigation And RAnging. Sonar uses sound propagation to navigate, detect objects underwater such as fish, or determine the nature and depth of the bottom. Many chart plotters offer sonar capabilities if connected to a transducer. The letter s after the name of a chartplotter often indicates this capability.

SOG

Speed over Ground. Speed of a boat compared to the land. The boat might be moving very quickly in the water and still show no speed over ground because of drift, tides and currents.

STW Speed Through Water

How fast a boat moves compared to the water it is in. It does not take in consideration tide or curent. It is possible to show 3 knots speed through water and have no speed at all when measuring speed over ground which is a measure of the speed of the boat compared to the land.

Transducer

Strictly speaking any device that transforms one form of energy into another form is a transducer. Practically speaking, most transducer used in the world of boats are sensors. For example an acoustic transducer reports depth or the presence of fish.

Vector Charts

These Charts are displayed on the fly by the plotter from stored data points. Vector images are smaller than raster images and information can be more easily attached and acted upon by the plotter. An example is water depth.

WAAS

Wide Area Augmentation System. This is an air navigation aid to augment GPS. It aims to improve the accuracy, availability and integrity of GPS. WAAS uses a network of ground based reference station in North America and Hawaii. These stations measure GPS variations and send the data to satellites which broadcast these corrections to WAAS enabled GPS receiver who integrate the information to improve accuracy. The service area includes Canada, the US and Most of Mexico and Alaska. For a more complete discussion see the Wikipedia entry on WAAS
Other Satellite Based Augmentation Systems (SBAS) are EGNOS in Europe and MSAS in Japan

Waypoint

Waypoints are sets of coordinates that identify a spot in the real world. Modern GPS allows user to set waypoints which have significance to that user. It could be a racing mark, home port, points along a route. The term waypoint is not a modern one and was in use long before GPS were around, is a reference point in physical space used for purposes of navigation. A waypoint could be a landmark used in orienteering for example.
Waypoint.org maintails fascinating lists of waypoints many marine.

XM WX

Comprehensive weather information service. Many chart plotters are capable of receiving this information if connected to a radio. It is a paid subscription. XM WX Satellite Weather

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Small Print

This information is for general knowledge only. It cannot be considered legal language. If you are writing official documents check your information and wording with the governing bodies of whatever project you are doing. I try to be accurate but nautical terms are notoriously changing. There are often many meanings depending on the era and place of usage, and I make mistakes.