Glossary

A/D: Analogue to Digital (A/D) refers to the conversion from analogue to digital signals.
Absolute Positioning: Positioning mode where a position is described with respect to a well-defined coordinate system. This system is commonly a geocentric system, whose point of origin coincides with the centre of mass of the earth.
Accessory: Optional part or extra to use with a Navman GPS navigation device.
Accuracy: How close a fix comes to the actual position.
Acquisition: The ability to find and lock-on to satellite signals for ranging.
Acquisition Time: The time it takes for a GPS receiver to acquire satellite signals and determine the initial position. Three satellites are needed for 2D and four for a 3D position fix.
Active Antenna: An antenna with an integrated low noise RF amplifier.
Active Leg: The segment of a route currently being travelled.
Active POI: A point of interest (POI) that is set to issue a warning when the operator is within a predetermined distance of its location.
Activity: Relates to data being transmitted from the vehicle. Activity is a history or log of events and can be based on the vehicle, the driver or a connected system such as a refrigerator or hydraulic lift. Standard activity includes time or distance updates, ignition on and off activity, Geofence entry or exit, low power, and GPS antenna connected or disconnected. (See Event also).
Alarms: Audio feedback on alert states, such as Too Shallow, Too Deep, Arrival radius, Low Fuel, etc. Some devices feature external output capability, allowing you to send alert state signals to speakers or lights.
Album: The portion of a hard disk or memory card used to store images taken by a camera
Algorithm: A special method used to solve a certain type of mathematical problem.
ALI: Automatic Location Identification. The automatic display of a subscriber’s telephone number, service address, position and supplementary information at a public safety answering point.
Almanac: A set of parameters included in the GPS satellite navigation message that a receiver uses to predict the approximate location of a satellite. The almanac contains information about all of the satellites in the constellation.
Almanac Data: Information transmitted by each satellite on the orbits and state (health) of the entire constellation. Almanac data allows the GPS receiver to rapidly acquire satellites as soon as it is turned on.
Altitude: The distance between a given position and the closest point on the WGS84 reference ellipsoid. This measure is positive outside the ellipsoid or above the geoid.
Altitude Hold: Technique allowing navigation by use of measurements from only three GPS satellites and an independently obtained altitude value.
AM: Amplitude Modulation (AM) is a method of encoding a message on the carrier signal by altering the height of the signal while keeping its frequency constant.
Ambiguity: The initial bias in a carrier-phase observation of an arbitrary number of cycles. The initial phase measurement made when a GPS receiver first locks-on to a GPS signal is ambiguous by an integer number of cycles because the receiver has no way of knowing the exact number of carrier wave cycles between the satellite and the receiver. This ambiguity, which remains constant as long as the receiver remains locked on the signal, is established when the carrier-phase data are processed.
Ambiguity Resolution: The mathematical process/algorithm for determining the value of ambiguities. Having a determined initial integer ambiguity value for each satellite, the integrated carrier phase measurement can be used as a precise distance measurement between the receiver and satellites. A solution using the carrier phase observations is known as an ambiguity fix.
Amplitude: Height of a radio wave as measured from an imaginary centre line to the wave peak.
Analogue: Electronic transmission characterised by variable waveforms that represent information.
Antenna: Hardware that receives incoming signals.
Antenna Gain: The ratio of a signal that is received or transmitted by a given antenna compared to an isotropic or dipole antenna, usually expressed in dB.
Antenna Type: The GPS antenna compatible with the device.
Anywhere Fix: The ability of a receiver to start position calculations without being given an approximate location and time.
API: Application Programming Interface. Refers to the published interface for third-party systems integration with the Fleet Manager database.
Apogee: The point where an object on an elliptical orbital path is farthest from the point in which that object orbits about.
Aquaducer: A combined sonar, water temperature and water speed transducer
Argument of Perigee: The angle or arc from an ascending node to the point of perigee of an Earth-centred orbit, measured in degrees of arc.
AS/A-S: Anti-Spoofing (AS/ A-S) is the process of encrypting the P-code by modulo-2 addition of the P-code and a secret encryption W-code. The resulting code is called the Y-Code. AS prevents an encryption-keyed GPS receiver from being “spoofed” by a bogus, enemy generated GPS P-Code signal.
Ascending Node: The point where an object’s orbit will cross a reference plane. An example is the point where a satellite orbit will cross the equatorial plane from south to north.
A-Scope: A sonar display showing the signals from the most recent sounding that is useful when adjusting gain and threshold settings.
A-Scope Perspective: 3-d representation of the sonar screen
ASF: The Additional Secondary Factor (ASF) is the error propagation time caused by radio waves slowing down as they pass over different terrain. This is in addition to slowing down as radiowaves pass over seawater.
Athermic: Heat reflective, for example athermic windshields are found in a number of manufacturers' vehicles.
ATIS function: Advanced Traveller Information System - used for vessel tracking and identification
Atomic Clock: A very precise clock that operates using the elements Caesium or Rubidium. A Caesium clock has an error of one second per million years. GPS satellites contain multiple Caesium and Rubidium clocks.
Auto Cal: Feature of electronic device that simplifies calibration procedure definition log.
Auto Range and Auto Gain: Two features used for optimising display information. Auto Range adjusts the vertical scale of the sounder reading on-the-fly to present maximum useful range from bottom to surface. Auto Gain compensates for noise produced by engine or speed interference, other sonic activity or water clarity.
Auto Tack: Automatic Autopilot action that drives the rudder so as to tack a sailboat while the user adjusts the sails
Auto zoom: Makes an object or area appear bigger or closer, or to decrease the area in view.
Automatic rerouting: A function of Navman's GPS navigation software that calculates the best route following a missed turn or manoeuvre.
Availability: A function of both the physical characteristics of the operational environment and the limitations of the transmitter facilities, it is the percentage of time where the services of a navigation system can be used within a given coverage area. Signal availability is the percentage of time that navigational signals from external sources can be used.
AVL: Automatic Vehicle Location (AVL) is the technique of using a navigation system, such as GPS, to determine a vehicle’s position.
AVM: Automatic Vehicle Monitoring (AVM) is the technique of using a navigation system to determine a vehicle’s position, which is then transmitted to a central unit that monitors and tracks the vehicle’s position and movement.
Avoid Area: An area or zone that should be avoided because of an accident, road construction, or for security reasons. Navman's navigation software lets you set your own Avoid Areas, for example congestion charging zones such as the one in Central London.
Azimuth: The horizontal direction from one point on the earth to another measured clockwise in degrees (0-360) from a north or south reference line. An azimuth is also called a bearing.

Backlighting: All colour and greyscale screens feature 16 levels of white backlighting. VHF radios feature 8 backlight levels, and Navman 3100 series instruments feature 4.
Back-on-Track: The Navman trade name for the software that automatically calculates the best new route following a missed turn or manoeuvre.
Bandwidth: The range of frequencies that compose a signal.
Base Station: GPS receiver at a known position, for purpose of collecting data for differentially correcting the data of other GPS receivers. The 'relative distance' between the base station's known position and the position calculated from the GPS satellite signals is the correction factor for the other GPS receivers. Corrections can be transmitted in real-time, as well as saved for later analysis.
Baseline: The resultant three-dimensional vector between a pair of base stations for which simultaneous GPS data is processed.
Basemap: The geographic map of a large area with roads of high national or international importance.
Baud: Unit of signalling speed corresponding to the number of discrete signal conditions, variations or bits per second. Ex: Signal period is 50 us, baud is then 20 kbps.
Beacon: Stationary transmitter that emits signals in all directions. Also called a non-directional beacon. In DGPS, the beacon transmitter broadcasts pseudorange correction data to nearby GPS receivers for greater accuracy.
Bearing: The angle between a position on the earth's surface with respect to true north by default. It is also the direction from a position to a destination, measured to the nearest degree (also called an Azimuth). In a GPS receiver, bearing usually refers to the direction to a waypoint.
Beeper: An audio output method of confirming button presses, alarms or external output ability.
Bias: Systematic errors that cause observed measurements to differ from true measurements by a constant value.
Binary Bi-phase Modulation: The phase modulation technique used to transmit a GPS signal. The phase of a carrier generated by a satellite is shifted by 180 degrees when there is a code or message binary signal level transition, either from 0 to 1 (normal to mirror image) or from 1 to 0 (mirror image to normal).
Bit: A unit of information in an electronic system expressed as one of two possible values. For example 0 or 1.
Block I, II, IIR, IIF: Designations given to the various GPS satellite generations. Block I satellites were prototypes that began launching in 1978. Block II consisted of 24 satellites that made up the fully operational GPS constellation declared in 1995. Block IIR consisted of replenishment satellites while IIF refers to the 'follow-on' group.
Boat speed with log: Certain transducers have paddlewheels that enable speed calculations relative to water flow. In addition, speed data can be logged to assist in fuel and travel time management.
Bottom Indication: The number of colours or grae levels used to indicate depth.
Bottom Lock: A view offered in split-screen sonar view. One window displays and 'locks' onto bottom detail. Bottom detail is constantly presented, either at an automatic or manually set zoom level. The second window displays either manual or automatic depth range.
BPC Modulation: Binary Pulse Code Modulation is the coding using pulses to represent binary numbers.
BPS: Bits Per Second. See Baud.
BPSK Modulation: Binary Phase Shift Key Modulation. Technique in which a binary message is imprinted on a carrier wave. Unlike amplitude and frequency modulation (AM/FM), BPSK modulation does not alter either, but instead, alters phase.
Brightness options: The range of settings on the camera, which enable the operator to set the light level when taking a photo.
Buttons: Another name for the small activating icon on computer screen or unit.

C/A code: Coarse Acquisition (C/A) Code is a family of PRN codes transmitted by GPS satellites, it is the standard positioning signal the GPS satellite transmits to the civilian user. It contains the information the GPS receiver uses to fix its position and time. Each satellite is assigned one of 32 unique codes in the family. Each code consists of 1,023 chips and is sent at a rate of 1.023 megabits per second. The code sequence repeats every millisecond. The C/A-codes are Gold codes - PRN codes that are distinguished by a very low cross correlation between any two codes (that is, they are nearly orthogonal). C/A-codes currently are transmitted only on the L1 frequency.
C/N0: Carrier to Noise Power Density (C/N0) is the ratio of the received carrier power over the noise power in a given bandwidth. It is normally expressed in dB. The higher the C/N0 value is, the higher the quality and strength of the received signal.
Calendar Alerts: Calendar Alerts are time-sensitive events that only trigger under specific conditions. There are two types of Calendar Alerts: Stationary Vehicle Alert and Unauthorised Activity Alert. You can configure Calendar Alerts to take effect on particular days and during particular hours. For example, the Stationary Vehicle Alert is routinely used during business hours, while the Unauthorised Activity Alert is used during out-of-office hours.
Calendar Template: The Calendar Template allows you to configure all the settings and rules that you want for the Stationary Vehicle and Unauthorised Activity Alerts and then save these as a template. You can then apply the saved Calendar Template to whichever vehicles you wish, quickly and easily.
Canned Messages: Defined (preset) messages created in the OnlineAVL application and sent to the MDT or M-Nav device (located in the vehicle). The preset messages are stored in the device and can be sent as a message or reply message to the OnlineAVL application.
Carrier: A radio wave that conveys or carries some kind of modulation.
Carrier Frequency: The frequency of the unmodulated output of a radio transmitter.
Carrier Phase: The accumulated phase of either the L1 or L2 carriers of a GPS signal, measured by a GPS receiver since locking onto the signal. Also called integrated Doppler.
Carrier Smoothed Code: A technique used by many GPS receivers to increase the accuracy of the C/A code. By measuring the distance from the receiver to the satellites (in counting the number of waves that carry the C/A code signal), the information can be used to 'smooth' the received code phase.
Carrier-Aided Tracking: A technique to improve accuracy by using the GPS carrier signal to get a more exact lock on the pseudorandom code.
Carrier-to-Noise Power Density C/N0: See C/N0
Carrier-Tracking Loop: A module in a GPS receiver that demodulates, or extracts, the satellite message by aligning the phase of the receivers local oscillator signal with the phase of the frequency shifted received carrier. Once the local oscillator signal is locked onto the carrier, its phase can be measured to provide the carrier-phase observation.
Cartography: The brand and version of chart data software you may add to the device.
CDI: Course Deviation Indicator (CDI) is a technique for displaying the amount and direction of crosstrack error (XTE).
CDMA: Code Division Multiple Access. CDMA refers to the type of cellular network used to communicate with the vehicle. It is a packet transmission protocol that the cellular modem must comply with in order for the vehicle to transmit activity data and receive messages.
Celestial data: Tide data, local time, moon phase, sunrise, sunset.
CEP: Circular Error Probable (CEP) is a measure of accuracy in navigation. CEP is the radius of the circle, inside of which the true horizontal coordinates of a position have a 50% probability of being located.
CH1903: Older Swiss geodetic datum, based on the Bessel-Ellipsoid.
CH1903+: Newer geodetic datum, in use since 1995.
Channel: In a receiver, it is the path for an electronic signal that is reserved for a specific satellite and used for various functions.
Charge indicator: The light signal or graphic display of a battery's power status.
Chart Datums: The number of chart configuration details, like local tides, for specific areas of the globe.
Chart display options: Lists the orientations charts may be presented on a device.
Chartplotter: GPS with built in and/or 3rd party electronic map.
Chip: Binary elements or digits that, unlike bits, convey no information. A PRN code consists of a sequence of chips.
Chip Rate: Chips per second. Ex: The C/A code has a chip rate of 1.023 MHz.
Civilian Code: See C/A-Code (Coarse Acquisition).
Clock Aiding: An accuracy enhancement technique in which an additional atomic clock (rubidium) provides accurate time to the receiver for calculating satellite clock frequency, phase bias and clock drift.
Clock Bias: The difference between a clock's indicated time and true universal time.
Clock Error: The difference between the synchronous GPS system time and the time held by the GPS receiver.
Clock Offset: A constant difference in the time held between two clocks.
C-Map: Provider of electronic charts.
C-Map Cartridge: C-Map are a third party chart data supplier for all Navman products. Extension cards may be inserted in C-Map cartridge slots.
C-Map User Card support: C-Map are a third party chart data supplier for all Navman products. User Cards are transferable user-defined data cards that store re-writable information.
CMG: Course Made Good (CMG) is the bearing from the 'active from' position (starting point) to present position.
Coastal Confluence Zone: The area extending from a harbour's entrance 50 nautical miles seaward or to the edge of the continental shelf (100 fathom curve), whichever is greater.
COCOM: Coordinating Committee for Multilateral Export Controls. All commercial GPS-receivers must conform to guidelines known as the COCOM-limits or restrictions, which dictate that such receivers will operate only at velocities less than 1,854 kph as well as at an altitude less than 18.3 km.
Code Phase GPS: GPS measurements based on the pseudo random code (C/A or P), instead of the carrier of that code.
Code Search: A search for the C/A Code alignment.
Code-Tracking Loop: A module in a GPS receiver used to align a PRN code sequence present in a signal coming from a satellite with an identical PRN code sequence generated within the receiver. Alignment is achieved by appropriately shifting the receiver-generated code chips in time so that a particular chip in the sequence is generated at the same instant its twin arrives.
COG: Course Over Ground (COG) is a vessel's track over the bottom as measured in degrees. The direction of movement relative to a ground position.
Cold Start: The ability of a GPS receiver to start providing position updates without the assistance of any almanac information stored in its memory. It is the power-on sequence when the GPS receiver downloads almanac data before establishing a position fix. Also called initialisation.
Compass: Instrument for showing direction.
Compliance: Another word for conformity, as in compliance standards.
ConEx: Connectivity Expander. An optional device that connects to the Halo Qube/Dome to connect additional sensors from external systems. A very versatile device, the ConEx can be used to monitor almost any conceivable peripheral system attached to the vehicle. Common uses include temperature monitoring, doors open or closed, hydraulic arm in operation, weight sensors, printers, trailer connected, etc.
Constellation: In reference to GPS, it either describes the set of satellites visible to a GPS receiver at a point in time or the entire set of GPS satellites in the Space Segment.
Continuous Continental Navigation: Map data that covers more than one country or region.
Control Point: A point in which, having assigned coordinates, is held fixed and used for other dependent purposes.
Control Segment: That portion of the Global Positioning System that consists of a master control station, monitoring stations and ground antennas, which monitor and update satellite signals and upload correction data to the satellites. This worldwide chain of monitoring and control stations is responsible for controlling and managing the GPS satellite constellation.
Coordinate: A set of numbers that describes location on or above the Earth.
Coordinated Universal Time (UTC): See Universal Time Coordinated (UTC)
Correlation Channel: A GPS receiver channel that utilises a delay lock loop to maintain an alignment (meaning peak correlation) between the GPS code and the copy of the code generated by the receiver.
Correlator: The GPS receiver component, analogue or digital, used to shift or compare the incoming signal with an internally generated signal. This operation is performed on the PRN codes, but may be used for other mixed signals. In the case of the L2 measurements for example, the L2 PRN code is not known, under policy of anti-spoofing.
Course: The direction from the beginning landmark of a course to its destination (measured in degrees, radians or mils).
Course To Steer: The maintained heading needed in order to reach a destination.
CRC: Cyclic Redundancy Check is a byte added to the end of a data packet, used to verify the data preceding it.
Cross Correlation: The signal derived from the correlating of the L1 frequency with the L2. This method counters the encryption of the P-Code to the secret Y-code and allows for the reconstruction of the carrier wave on L2. However, the resulting carrier has a reduced signal quality when compared to the unencrypted signal.
Cross-track: Deviation distance left or right from track or course
Crosstrack Error (XTE/XTK): The difference between a vessel's actual position and its desired position on a given heading. This is usually measured as a range error in nautical miles but may also be expressed graphically using symbols. In other words it is the distance off the desired course in either direction.
Custom POI: A point of interest (POI) defined by the user.
Customer Site: A Customer Site is a location drawn on the Map in OnlineAVL by the user (a blue boundary). It is typically used to mark a location of interest such as a customer's premises, but can be used for almost anything (staff houses, suppliers, lunch stops, fuel stations, etc). These sites are then used for Reports so that you can see when a vehicle has visited a site and how long it has been there. For a Site to work for reports, the vehicle must generate activity while it is inside the site, such as an 'ignition off' event. There is no upper limit for the number of Customer Sites you can use. (See also Geofence.)
Cutoff Angle: The minimum satellite elevation angle (above the horizon) that avoids blockage of sight, multipath errors, or unacceptably high Tropospheric or Ionospheric delay values. This angle may be preset in the receiver, or applied during data post-processing. A typical GPS cutoff angle is 15 degrees.
Cycle Slip: A discontinuity in GPS carrier-phase observations, usually of an integer number of cycles, caused by temporary signal loss. If a GPS receiver loses a signal temporarily, due to obstructions for example, when the signal is reacquired there my be a jump in the integer part of the carrier-phase measurement due to the receiver incorrectly predicting the elapsed number of cycles between signal loss and reacquisition.

Data header: Numerical values of data shown at the top of the screen.
Data Message: A message included in the GPS signal that reports the satellite location, clock corrections and health. Included is approximate information about the other satellites in the system as well.
Datum: The coordinate system used to define position on the earth surface. It is a mathematical model designed to fit part of the Earth's surface (current default is WDS 84). Latitude and longitude lines on a paper map are referenced to specific map datum. The map datum for a GPS receiver needs to match the datum listed on the corresponding paper map.
dB: Decibel (dB) is the convention for relative power ratio in expressing relative powers (such as output/input).
dBHz: Decibel per Hertz (dBHz) is the magnitude of power or voltage expressed in dB, referenced for a bandwidth of 1 Hz.
dBiC: Decibel-Isometric-Circular (dBiC) is the measure of power relative to an isometric antenna having circular polarisation.
dBm: Decibel per Milliwatt (dBm) is dB referenced to one milliwatt.
dBW: Decibel per Watt (dBW) is dB referenced to one watt.
DC: Direct Current (DC) is the electrical energy that flows continuously in one direction.
Dead Reckoning: The technique of determining position by computing distance travelled on a given course. Distance travelled is determined by multiplying speed by elapsed time.
Delay Lock: Technique utilised by a receiver, where a received code is compared with an internally generated code. The internally generated code is time shifted until the two codes match.
Delta Pseudorange: (see Reconstructed Carrier Phase)
Depth Range: The range between which a sounder delivers effective data.
Destination wizard: An easy-to-use software interface to enter a physical address.
Detour: An alternative route.
DGPS: Differential GPS (DGPS) is a technique to improve GPS accuracy that uses pseudo-range errors recorded at a known location to improve the measurements made by other GPS receivers within the same general geographic area. The most common form of DGPS involves determining the combined effects of navigation message ephemeris and satellite clock errors at a reference station and transmitting pseudo-range corrections. DGPS reduces the effect of SA, propagation delay, etc. and can improve position accuracy to greater than 10 metres.
Diesel flow vs RPM graph: The ability to plot fuel against engine revolutions to determine effective efficiency.
Differential Correction: A process for neutralising man made and naturally occurring errors of the GPS signal. This requires the use of a separate GPS receiver set up at a position with a known location. The receiver at the known location computes its location using the GPS satellite data and compares this position with the known value of its actual known position. This difference is the error of the transmitted GPS signal. This differential value is then used for correcting, either in real-time or during post processing, the positions collected by other GPS receivers during the same time period, which were observing the same satellites.
Digital: Information is expressed, stored and transmitted by either analog or digital means. In a digital form, this information is seen in a binary state as either a 1 or 0 (high or low voltage).
Dithering: Introducing errors into the satellite clock readout on GPS signals for the purpose of degrading GPS position accuracy for civil users.
DOD: The US Department of Defense (DOD). The DOD manages and controls the Global Positioning System.
Dodge: Manually initiated course change manoeuvre
DOP: Dilution of Precision (DOP) is a dimensionless number that accounts for the contribution of relative satellite geometry to errors in position determination. DOP has a multiplicative effect on the user equivalent range error (UERE). Generally, the wider the spacing between the satellites being tracked by a GPS receiver, the smaller the position error. The most common quantification of DOP is through the position dilution of precision (PDOP) parameter. PDOP is the number that, when multiplied by the root mean square (RMS) UERE, gives the RMS position error. Other DOPs include the geometric dilution of precision (GDOP), horizontal dilution of precision (HDOP) and vertical dilution of precision (VDOP).
Doppler Aiding: A signal processing strategy that uses a measured Doppler shift to help the receiver smoothly track the GPS signal, thereby enabling a more precise velocity and position measurement.
Doppler Effect/Shift: The shift in the frequency of a received signal due to the relative motion of the transmitter and receiver.
Doppler Search: The acquisition of a GPS signal is a search process, where, like the tracking process it requires replication of both the code and the carrier of the satellite vehicle (SV) to acquire the SV signal. The range dimension is associated with the replica code and the Doppler dimension is associated with the replica carrier. From the user's velocity and the SV line-of-sight Doppler, the total line-of-sight Doppler can be determined, which is used in the Doppler search pattern for the SV.
DOSS: Direct Sequence Spread Spectrum (DOSS) is the most practical, all digital version of Spread Spectrum (SS), which uses a locally generated pseudo noise code to encode digital data for transmission. This locally generated code runs at a much higher rate than the data rate. The data for transmission is logically modulo-2 added (OR) with the faster pseudo noise code and composite pseudo noise and data is passed through a data scrambler to randomise the output spectrum (to remove discrete spectral lines). A direct sequence modulator is used to double sideband suppressed carrier modulate the carrier frequency to be transmitted. The resultant DAB suppressed carrier AM modulation can be seen as binary phase shift keying (BPSK). Carrier modulation other than BPSK is possible with direct sequence; however, binary phase shift keying is the simplest and most commonly used SS modulation technique.
Double Difference: A GPS observable formed by arithmetically differencing carrier phases simultaneously measured by a pair of receivers tracking the same pair of satellites. First, the phases obtained by each receiver from the first satellite are differenced. Second, the phases obtained by each receiver from the second satellite are differenced. And third, those differences are differenced. This procedure removes essentially all of the satellite and receiver clock errors. Although primarily used with carrier phases, the procedure can also be applied to pseudo-ranges.
DR: See Dead Reckoning (DR).
Drift: The rate of a vessel's departure from a given course as measured in knots.
Drive-Away: A ready-to-use Navman GPS navigation device that simply needs unpacking, installing and turning on. Drive-Away is a registered trademark of Navman.
DRUMS: Distance Root Mean Square (DRUMS) is a measurement used to describe the accuracy of a fix. It is twice the square root of the sum of the squares of all radial errors surrounding a true point divided by the total number of measurements.
DRY: Data Terminal Ready is a signal from a communications program to a modem that indicates that the program has been loaded and is ready to run.
DSC: Digital Selective Calling (DSC) is a radio feature allows automated "mayday" signalling and private ship to ship calls
DSL: Digital Signal Processor (DSL) is a special type of coprocessor designed for performing the mathematical operations of signal processing.
DTG: Distance to go (DTG).
Dual Frequency: Sonar that transmits at two different frequencies for improved performance. A high frequency (usually 200kHz) for high definition and a low frequency (50kHz or 83kHz) for wider beam angle and deeper depth
DUTCH: Desired Track (DUTCH) is the compass course between the "from" and "to" waypoints.

E911: Enhanced 911 (E911) is when automatic number identification and location information is provided to the 911 operator, it becomes 'enhanced.' In the United States, 911 is a nationwide universal telephone number that provides the public with direct access to a Public Safety Answering Point (PAP).
EARP: Effective Radiated Power (EARP) is the relative gain of a transmitting antenna with respect to the maximum directivity of a half wave dipole, multiplied by the net power accepted by an antenna from the connected transmitter.
EGOS: European Geostationary Navigation Overlay Service (EGOS) is the system of geostationary satellites and ground stations developed in Europe to improve the position and time calculation performed by the GPS receiver.
EKE: Earth Centred Earth Fixed (EKE) is the Cartesian coordinate system in which the origin is the centre of the earth. In actuality it is the centre of a datum, which best fits the size and shape of the earth.
Electromagnetic Spectrum: The distribution of energy in the form of electromagnetic waves arranged in order of their frequencies or wavelengths.
Elevation: The distance above or below average sea level.
Elevation Mask Angle: See Cutoff Angle.
Ellipsoid: Mathematical figure formed by revolving an ellipse about its minor axis. Also referred to as a spheroid, two values define an ellipsoid: The length of the semi-major axis a and the flattening, f = (a-b)/a, where the value b is the length of the semi-minor axis.
Ellipsoid Height: The vertical distance above an ellipsoid. GPS receivers output vertical position with respect to the WGS84 datum.
EMC: Electromagnetic Compatibility (EMC) is the capacity of a device to function within an intended electromagnetic environment.
EMI: Electromagnetic Interference
Encryption: The process of altering data so that only an intended receiver can read it. To decipher the data, the receiver must have the proper decryption key. In GPS, the military P code is encrypted so that civilian users cannot utilise it, as well as to give it anti spoofing properties. This makes it difficult for an enemy to interfere with or transmit a false signal. The encrypted code is called the Y code.
EOW: End of Week (EOW), also called the week number rollover (WNRO), is a rollover of the internal GPS clock. The first rollover was on August 21, 1999. The necessity for this rollover exists because of the incrementing count the GPS system uses in the number of weeks. Starting at "0000" corresponding to January 6, 1980 the GPS system week time reached a maximum number of bits with the number 1023 by August 21, 1999 and therefore on that day at 23:59:47 UTC, the GPS clock was reset to week "0000."
EPEE: Estimated Position Error (EPEE) is a measurement of horizontal position error in feet or metres based upon a variety of factors including DOP and satellite signal quality.
EPEE: Expected Horizontal Position Error (EPEE) is the expected error in position under given conditions.
Ephemeris: Current satellite position and timing information transmitted as part of the satellite data message. A set of ephemeris is valid for several hours.
Ephemeris Errors: Errors present in the Ephemeris data. Broadcast errors are typically within a few metres and precise ephemeris errors are within the decimetre level. These errors can be corrected by differential correction (DGPS) or in double differencing.
Epoch: A particular instance of time or date for which values of data are given or a given period of time during which a series of events take place.
Epoch Rate: The rate at which a receiver samples observational data from a satellite.
EPROM: Electrically Erasable Programmable Read Only Memory (EPROM) is the memory on a chip that can be stored and erased electronically yet does not lose data when power is removed. Although it carries the ROM title it can be written to, slowly. Therefore its only real practical purpose is to store data which will not change often.
EPROM: Erasable Programmable Read Only Memory (EPROM) chips store long term information and do not require power to retain data, unlike volatile memory such as RAM. They are erased by exposure to UV light and reprogrammed with PROM burners.
Error Budget: A set of individual error sources with statements of the percentage of the total system error contributed by each source.
ETA: Estimated Time of Arrival (ETA) is the time of arrival to destination.
EVE: Expected Vertical Position Error (EVE) is the expected error in position under given conditions.
Event: An event is a specific type of Activity generated by the Halo/Qube in the vehicle. An event is typically related to an action or trigger and relates to a particular moment in time. An event includes the type of event, the time and date and the GPS location of the vehicle at the time the event occurred.
Event list: The record of traffic event messages received.

FAQ: Frequently Answered Question
Fast Multiplexing Channel: Single channel that rapidly and sufficiently samples multiple satellite ranges in order to recover the data message.
Fast Switching Channel: See: Fast Multiplexing Channel.
FAT: Fast Fourier Transform (FAT) is the procedure for calculating discrete frequency components from sampled time data.
Favourite: A physical address with personal importance that is designated by the user.
Firmware: The software of a receiver consisting of coded instructions that comprise the receiver functions and data processing algorithms, embedded as integral components of the internal circuitry.
First fix: The initial instance when the geographical position of a GPS receiver is established.
Fish arch: The default representation of a sonar echo from a fish on your screen.
Fish finder: Sonar with fish detection capability.
Fish Forecaster: A data field that predicts how good the fishing conditions are, based on historical temperature and barometric pressure readings
Fish Symbol: An alternative view-state for target detail. Fish icons replace sonar data when the data approximately fish target readings. Depth numbers may also be super-imposed for every target acquired.
Fix: Defining position, where two lines such as latitude and longitude cross, as determined by one or more navigation aids or techniques.
Flash Memory: Non-volatile memory (retaining memory when power is off) similar to an EPROM, but with the ability to be electronically erased and written to. This enables the flash memory to be easily updated, appended or edited. See also: EPROM.
Flattening: Pertaining to one of the values which define an ellipsoid: f = (a-b)/a\ {also f = 1 - sqrt(1-e^2) where a = semi-major axis b = semi-minor axis e = eccentricity}
Fleet: Refers to all of the vehicles belonging to a customer. A fleet may be grouped in sub-groups such as by vehicle type or city.
Fleet Manager: Refers to the overall Navman Fleet Manager solution. Fleet Manager is an end-to-end fleet management solution comprising in-vehicle tracking hardware, data service packages, desktop software, database hosting and other services including technical support.
Flow Sensor: Sensor for measuring flow of liquids
FOC: For NAVSTAR, Full Operational Capability (FOC) occurred in 1994, when 24 operational GPS satellites (Block II/IIA) began functioning in their assigned orbits and were available for navigational use.
FP: Floating Point (FP) is a mathematical way of representing large numbers by using coefficients, a base and exponents to specify scale, range and magnitude of numbers. In computing systems the IEEE 754 standard is used.
FR4 substrate: Flame Retardant type 4 - the usual base material from which plated-through hole and multi-layer printed circuit boards are constructed. The type '4' indicates woven glass reinforced epoxy resin.
Frame and Subframes: The GPS Navigation Message contains time tagged bits that mark the time of transmission by the SV. A data bit frame has 1500 bits, which consist of five 300-bit subframes. Every thirty seconds a data frame is transmitted, therefore every 6 seconds contains a subframe. 25 frames make up the complete Navigation message sent over a 12.5-minute period.
Frequency: The number of waves passing a specific point within a unit period of time, expressed in Hertz (cycles per second). Frequency is equal to 1/T, where T is the period in seconds.
Frequency Band: A range of frequencies, in a particular region.
Frequency Spectrum: The distribution of signal amplitudes as a function of frequency.
Frozen Start: This acquisition state occurs when there are no valid internal data sources available to a receiver.
FRP: The Federal Radio-navigation Plan (FRP) is an official US government document, published biennially, that outlines radio-navigation planning and policy
Fuel Economy: The ability to calculate rate of change in fuel usage over time or distance.
Fuel Range: An estimate on the distance your remaining fuel will take you for.
Fuel Used / Fuel Remaining: The ability to measure quantities of fuel used and stored.
Fundamental Frequency: The fundamental frequency (F) used in GPS is 10.23 MHz. The carrier frequencies L1 and L2 are integer multiples of this frequency. L1 = 154F = 1.57542 GHz. L2= 120F = 1.22760 GHz.

GaAs: Gallium Arsenide (GaAs) is a semiconductor material used in high frequency circuits.
Gain: Amplification of received signal. In this case mostly the echo from a transmitted sonar signal.
Galileo Positioning System: A proposed alternative to the US GPS system by the European Union, it is also a satellite navigation system. Planned operational by 2010, the primary goals of Galileo is to provide greater precision to all users than currently available, improved northern latitude coverage and a positioning system that will be available during wartime.
GDOP: Geometric Dilution of Precision (GDOP) is a factor used to describe the effect of the satellite geometry on the position and time accuracy of the GPS receiver solution. The effects of the combined errors of four variables (latitude, longitude, altitude and time) on the accuracy of a three-dimensional fix. The lower the value of the GDOP parameter, the less the error in the position solution. Related indicators include PDOP, HDOP, TDOP and VDOP.
Geocentre: The centre of the earth.
Geodesy: The branch of applied mathematics that deals with the measurement, curvature and shape of the earth.
Geodetic: Geographic or pertaining to geodesy. Latitude and longitude readings are geodetic coordinates.
Geodetic Datum: A specifically oriented reference ellipsoid. Typically, eight parameters are required to define a geodetic datum: two to specify the dimensions of the ellipsoid, three to specify the location of its centre with respect to the earth's centre of mass and three to specify the orientation of the ellipsoid with respect to the average spin axis of the earth and the Greenwich reference meridian. Also called a horizontal datum.
Geodetic Height: The height of a point above an ellipsoidal reference surface. Also known as ellipsoidal height. The difference between the geodetic height of a point and its orthometric height is equal to the geoidal height.
Geodetic Surveys: Global surveys to establish control networks for accurate land mapping.
Geofence: A Geofence is an area drawn on the Map in OnlineAVL by the user (an orange boundary). It is similar to a Customer Site but Geofence's are sent to and stored in the vehicle. This means that the vehicle is always aware of its location in relation to a Geofence and can report the moment it enters or exits a Geofence as an Event. Geofences are invaluable for creating Alerts if a Vehicle enters or exits a Geofence. Geofence Reports are more detailed than Customer Sites as they tally the exact time spent inside of a Geofence and the mileage for the vehicle inside that Geofence. There is no upper limit for the number of Geofences that you can create, but the Halo Qube/Dome is limited to 50 that it can store.
Geoid: The undulating, but smooth, equipotential surface of the earth's gravity field, which coincides most closely with mean sea level. The geoid is the primary reference surface for heights.
Geoid Undulation: The height of the geoid relative to an ellipsoid. A positive value above the ellipsoid, negative when below, the value is used to convert an MSL elevation to an ellipsoid height.
Geometric Quality: Probable accuracy of a position fix found by taking the relative position of satellites into consideration.
Geostationary Satellites: Those satellites situated in a constant orbit position relative to a given area of the globe with the purpose of maintaining constant coverage of that area.
GIS: Geographic Information System (GIS) is the computer based system capable of collecting, managing and analysing geo-spatial data. Functions include storing and manipulating maps, displaying the results of data queries and conducting spatial analysis.
GLONASS: Russian Global Navigation Satellite System (Globallaya Navigatsionnaya Sputnikovaya Sistema). The operation of this system is similar to GPS.
GMT: Greenwich Mean Time (GMT) is the mean solar time for the meridian at Greenwich, England, used as a basis for calculating time throughout most of the world. Also called universal time.
GNSS: Global Navigational Satellite System (GNSS) is the organisational concept of incorporating GPS, GLONASS and other space and ground based segments to support all forms of navigation.
GOTO: Function for giving you direction to a waypoint on your chartplotter.
GPIO: General Purpose Input/Output (GPIO) is used in embedded electronics, a set of IO ports configured for either input or output, which enable the support of different functions to the system designer.
GPRS: General Packet Radio Service. GPRS is the packet data protocol on the GSM network. It is used to transmit activity data from the vehicle and to send messages out to the vehicle.
GPS: Global Positioning System (GPS) is a global navigational system based on 24 satellites orbiting the earth at an altitude of 12,000 miles and providing very precise, worldwide positioning and navigation information 24 hours a day, in any weather. Also called the NAVSTAR system.
GPS (System) Time: The time scale to which GPS signals are referenced. GPS Time derives a composite clock consisting of all operational monitor stations and satellite atomic clocks. It is steered to keep within about 1 microsecond of UTC, as maintained by the Master Clock at the US Naval Observatory, ignoring the UTC leap seconds. At the integer second level, GPS Time equalled UTC in 1980, but currently, due to the leap seconds that have been inserted into UTC, it is ahead of UTC by 14 seconds.
GPS almanac: The transmitted data containing the approximate orbit paths of all 24 GPS satellites for the coming months.
GPS fix: The established geographic position of a GPS receiver, calculated by processing GPS satellite signals.
GPS ICD-200: GPS Interface Control Document (GPS ICD-200) is a government document containing the full technical description of the interface between the space and user segments. GPS receivers must comply with this specification if they are to process the GPS signals properly.
GPS logging: Adding information to a software file created to record route coordinates
GPS status: The visual representation of information received from GPS satellites.
GPS Week: The number of elapsed weeks (modulo 1024) since the week beginning January 6, 1980. The week number sequentially increments at Saturday/Sunday midnight in GPS (System) Time.
Greenwich Reference Meridian: The zero meridian (0i) used as a reference line from which longitude east and west is measured. It passed through Greenwich, England.
Grid: A pattern of regularly spaced horizontal and vertical lines forming square zones on a map used as a reference for establishing points.
Ground speed: The velocity travelling relative to a ground position. Typically measured in knots (nautical miles per hour).
Ground wave: A radio wave that travels along the earth's surface.
GSM: Global System for Mobile communication. GSM is a type of cellular communications network and an alternative to CDMA.
Gyro: Gyroscope. An internal device used to measure the change of attitude (the rate of pitch, roll and yaw). Gyros normally consist of a rotating mass of a wheel inside a frame that allows it to turn in any direction. When the wheel spins, it is able to maintain a constant orientation in space. They are usually included in inertial sensors.

HAE: Height Above Ellipsoid. (HAE) is the height determined with relation to the Reference Ellipsoid (in GPS WGS84). Initially, coordinates are derived in the Cartesian coordinate system and then transformed to a latitude, longitude and ellipsoidal height through known formulae for the established datum.
Halo Dome: Navman GPS tracking device. The Halo Dome is an externally mounted device best suited for buses, trucks, vans, trailers and earth-moving equipment. The Halo Dome is extremely tough and weather-proof. (See also Halo Qube)
Halo Qube: Navman GPS tracking device. The Halo Qube is designed to be fitted inside the vehicle (under the seat or dashboard). It is an all-purpose tracking device that can be used in cars, vans, trucks, etc. The Halo Qube is built tough in an aluminium case; but unlike the Halo Dome, the Halo Qube is not weather proof. The Halo Qube is easy to install and service as well as being discrete.
HDOP: Horizontal Dilution of Precision (HDOP) is the effects on accuracy of the combined errors in a two dimensional fix obtained from crossing two lines of position.
Heading: The direction in which a vehicle is moving. This may differ from actual course over ground due to winds, sea conditions, etc.
Heat reflective windscreen/windshield: A vehicle's front window which has specially treated or designed to reflect infrared radiation.
Height Aiding: An accuracy enhancement technique in which the known height of the receiver is entered into the navigation solution, which in effect provides another satellite range.
Hertz (Hz): A unit of measure; One cycle per second (1/s).
HMSL: Height above Mean Sea Level (HMSL) is the height of a station measured along the local plumb line direction through that station, above the Geoid surface.
Hot Start: Start up mode of the GPS receiver when it has or is initialised with valid ephemeris, almanac and time.
HOW: The second word in each sub frame of the navigation message is the Hand-Over Word (HOW). It contains the Z-count at the leading edge of the next sub frame and is used by a GPS receiver to determine where in its generated P-code to start the correlation search process.

I/O: Input/Output (I/O) is the transfer of data into and out of a system.
iCN: Interactive Car Navigation (iCN).
IDGPS: Inverse DGPS (IDGPS) is a method in which the mobile receiver reports to a base station its navigational solution as well as the satellites used to create it. The base station maintains a record of pseudorange corrections and associated times of applicability from a reference receiver, then selects the pseudorange corrections corresponding to the satellites used in the solution. The pseudoranges are then time propagated to agree with the times of applicability for each receiver's navigation solution.
Idle / Idling: When a vehicle's engine is on but no movement is detected from the vehicle.
IF: Intermediate Frequency (IF) is a frequency in which a carrier frequency is shifted as an intermediate step in transmission or reception.
IGRF: International Geomagnetic Reference Field (IGRF) is a model for empirical representation of the Earth's magnetic field, recommended for use by the International Association of Geomagnetism and Aeronomy (IAGA). The IGRF model represents the primary or core field without external sources. The model uses the usual spherical harmonics expansion of the scalar potential in geocentric coordinates. The model coefficients are based on all available data sources including geomagnetic measurements from observatories, ships, aircrafts and satellites.
Inclination: One of the orbital parameters that describes the orientation of an orbit. It is the angle between the orbital plane and a reference plane, the plane of the celestial equator for geocentric orbits and the ecliptic for heliocentric orbits.
Indians: There are two basic architectures for which memory storage is based upon: Big Endean and Little Endean. These refer to the order in which the bytes are stored in memory.
In-Hull: Relating to In-hull sonar transducers that is mounted on the inside of the hull.
Initial Operating Capability: For NAVSTAR, this is defined as the capability available when 24 GPS satellites (Block I/II/IIA) are operational in their assigned orbits, ready for navigational use.
Initialisation: The first time a GPS receiver orients itself to its current location. After initialisation has occurred, the receiver remembers its location and acquires a position more quickly because it doesn't need a large amount of satellite information. Entering such data as time, time offset, approximate position and antenna height into a receiver (cold start with no almanac) to manually help the unit find and track satellites, is also called initialisation. See Initial Acquisition.
Inmarsat: An international consortium chartered in the mid-1970s to provide improved maritime public correspondence and radio determination capabilities.
Instant Fuel Flow: The ability to detect the rate of fuel flow.
Integer Ambiguity: The unknown number of wavelengths between a satellite and a receiver's antenna. Resolving the ambiguity for each satellite is the essential task of differential processing and land surveying applications.
Integrity: The ability of a system to supply timely warnings in the event of a loss of navigation solution, excessive noise or other factors affecting measured position.
Interface: The shared boundary between systems and programs or users.
Interference: Any distortion of the transmitted signal that impedes the reception of the signal at the receiver (same as noise).
Interferometric Differencing: A variation of phase differencing in which two different antennas sample the GPS signal wave front at two locations and then feed the information into a single amplifier and mixer (interferometer) in which phase difference observations are made.
IODE: Issue of Data Ephemeris (IODE) is part of the Navigation Message Data Structure. The navigation message is transmitted by the satellite on the L1 data link at 50 Bps.
Ion: An electrically charged particle formed by either adding or taking away electrons from neutral particles.
Ionisation: The process by which atoms form electrically charged particles called ions.
Ionosphere: The layer of the atmosphere approximately 30-300 miles above the earth's surface that contains electrically charged particles (ions). These charged particles interfere with or distort transmissions of electromagnetic signals through the layer.
Ionospheric Delay: The phase delay dependent on the electron content of the atmosphere affecting the carrier signals.
Ionospheric Refraction: The change in the propagation speed of a signal as it passes through the ionosphere.
IPx6: Water proofness rating. (Splash proof)
IPx7: Water proofness rating. (Immersable)

JIS7: 7 bit code to convert JIS data to an ASCII format
JPO: Joint Program Office (JPO) exists within the U.S. Air Force Systems Command, Space Systems Division and is responsible for managing the development and production of the GPS system. Representatives from each branch of the U.S. military, the U.S. Department of Transportation, Defense Mapping Agency, NATO member nations and Australia make up the staff.
Julian date: Number of days elapsed since the 1st of January 4713 B.C. in the Julian calendar. GPS time zero is defined to be midnight UTC, Saturday/Sunday, 6 January 1980 at Greenwich. The Julian date for GPS time zero is therefore 2,444,244.5.

Kalman Filter: An optimum mathematical procedure for recursively estimating dynamically changing parameters, such as the position and velocity of a vessel, from noise contaminated observations.
Keel-offset: Keel offset is a depth correction representing the vertical distance between the depth transducer and the location from which the depth is to be measured.
Keplerian Elements: A set of six parameters that describe the position and velocity of a satellite in purely elliptical (Keplerian) orbit. These parameters are the semi major axis, the eccentricity of the ellipse, the inclination of the orbit plane to the celestial equator, the right ascension of the ascending node of the orbit, the argument of perigee and the time the satellite passes through the perigee.
Keypad: Navman device buttons are laser-etched silicone rubber. All current device buttons are backlit, with the exception of the 2100 series.
Kiloherts (kHs): 1,000 cycles per second (Hz)
Kinematic: Pertaining to motion or moving objects.
Kinematic Positioning: Positioning a continuously moving platform by using GPS carrier-phase data while operating in a differential mode.
Kinematic Surveying: A precision differential GPS surveying technique in which the roving user does not need to stop to collect precision information. metre to centimetre-level accuracy is available using mode, dual-frequency, carrier-phase measurement techniques.

L1 Frequency: One of the two ultra high radio frequencies transmitted by NAVSTAR GPS satellites. This carrier frequency of 1575.42 MHz transmits both C/A (Standard Positioning Service) and P (Precise Positioning Service) code. It also carries the navigation message.
L1 Frequency Band: One of the two ultra high radio frequencies transmitted by NAVSTAR GPS satellites. This carrier frequency of 1575.42 MHz transmits both C/A (Standard Positioning Service) and P (Precise Positioning Service) code. It also transmits carries the nav message.
L1 Signal: The primary L band signal transmitted by each GPS satellite at 1575.42 MHz. The L1 broadcast is modulated with the C/A and P codes, as well as with the navigation message.
L2 Frequency: One of the two ultra high radio frequencies transmitted by NAVSTAR GPS satellites. This carrier frequency of 1227.6 MHz carries the P (Precise Positioning Service) code exclusively.
L2 Frequency Band: One of the two ultra high radio frequencies transmitted by NAVSTAR GPS satellites. This carrier frequency of 1227.6 MHz carries the P (Precise Positioning Service) code only.
L2 Frequency Band: One of the two ultra high radio frequency bands (1246.4375 - 1256.5000 Mhz) transmitted by the GLONASS satellites. Unlike the NAVSTAR satellites, each GLONASS satellite transmits on a separate frequency within this band.
L2 Signal: The secondary L band signal transmitted by each GPS satellite at 1227.60 MHz. The L2 broadcast carries the P code and navigation message.
LAAS: Local Area Augmentation System (LAAS) is the implementation of DGPS to support aircraft landings in a local area (20 mile range).
LADGPS: Local Area DGPS (LADGPS) is a form of DGPS in which the user's GPS receiver receives real-time pseudo-range and, possibly, carrier-phase corrections from a reference receiver generally located within line of sight. The corrections account for the combined affects of navigation message ephemeris and satellite clock errors (including the effects of SA) and usually, atmospheric propagation delay errors at the reference station. With the assumption that these errors are also common to the measurements made by the user's receiver, the application of the corrections will result in more accurate coordinates.
Languages: The languages operation and installation manuals for a device are available in. The actual device features additional languages which are user-selectable.
Latitude: The distance north or south of the equator as measured in degrees (0-90), with 1 degree of latitude equalling 60 nautical miles. Therefore 1 minute of latitude equals 1 nautical mile. Latitude is constant on a parallel. One must distinguish between astronomical and geodetic (for example, World Geodetic System of 1984 [WGS 84] latitude).
L-Band: The segment of the microwave portion of the radio spectrum nominally between 1 and 2 GHz.
LCD: Liquid Crystal Display. Most screens on marine instruments are based on this technology.
Lighting options: The range of setting on the camera, which enable the operator to customise the light exposure when taking a photo.
Line of Sight: The unobstructed view of an object. GPS receivers must have line of sight to receive signals from satellites. Objects such as tall buildings and bridges can block the line of sight needed by a receiver to obtain a navigational solution.
LLA: Latitude, Longitude, Altitude (LLA) is a Geographical coordinate system used for locating positions with respect to the Earth's surface.
LNA: Low Noise Amplifier (LNA) is the preamplifier between the antenna and receiver. For effectiveness, it should be located as near to the antenna as possible. It is designed to contribute the least amount of thermal noise to a received signal.
Log: Typically a speed or distance device recording function
Longitude: Distance east or west from the prime meridian as measured in degrees, with each degree becoming smaller the closer it comes to either of the poles. At the equator, 1 degree of longitude equals 60 nautical miles. Along the meridian the longitude is constant. One must distinguish between astronomical and geodetic (for example, World Geodetic System of 1984 [WGS 84]) longitude.
LOP: The locus of points has a constant measurement (such as range, range difference). A fix is determined by crossing two lines of position (LOPs).
LORAN: Long Range Radio Direction Finding System (LORAN) is a radio navigation aid operated and maintained by the US Coast Guard. It is used as a supplemental system for harbour approach and inland navigation. LORAN C is used in civil aviation.
LORAN-C: Long range navigation system that determines position by comparing the arrival times of radio signals with two or more master/secondary station pairs. Used in civil aviation.
LSB: Least Significant Bit (LSB) is the bit (or byte) with the smallest significance, normally the rightmost bit.
LTP: Local Tangent Plane (LTP) is a coordinate system based on the dimensions North, East and down sense. North and East are measured in degrees or radians, while down is the height below the WGS84 ellipsoid in metres.

M/S: Metres Per Second (m/s) is a unit of velocity.
M/S^2: Metre Per Second Per Second (m/s^2) is a unit of acceleration.
M/S^3: Metre Per Second Per Second Per Second (m/s^3) is a unit of jerk or impulse.
Magnetic Deviation: The error in a magnetic compass reading caused by the difference between the true north pole and the magnetic north pole. This difference is caused by changes in the Earth's magnetic field at different locations on the planet. Also referred to as magnetic variation.
Magnetic North: Represents the direction of the north magnetic pole from the observer's position. The direction a compass points.
Magnetic Variation: See: Magnetic Deviation.
Map Display: A graphic representation of a geographic area and its features.
Mask Angle: See Cutoff angle.
MB: Megabyte (MB) is a unit used to measure data size. Customers usually receive a bandwidth quota for vehicle data and messaging measured in megabytes per month. A MB is 2^20 bytes, 2^23 bits.
MCB: Main Circuit Breaker (MCB) is used to isolate equipment from a DC circuit
MDT: Mobile Data Terminal (MDT) is the device fitted onto the dashboard of a vehicle, for two-way messaging between the vehicle and the OnlineAVL application.
Megahertz (MHz): One million cycles per second (Hz)
Memory: Non-Volatile Memory - Stores all settings when turned off.
Memory card: A postage stamp-sized data storage unit.
Memory card reader: An electronic device for reading and writing of different types of memory cards (SD, MMC).
Menu: A list of program options when used in relation to Navman GPS navigation devices.
Messaging and Navigation: M-Nav device fitted onto the dashboard of a vehicle, for two-way messaging between the vehicle and the OnlineAVL application. In addition, the device is a navigation unit able to route a driver to a location. The co-ordinates (street, road etc) of a location can be sent from the OnlineAVL application to the device in the vehicle. (See also M-Nav)
MHz: Megahertz (MHz) 9s one million cycles per second (Hz)
Microstrip Antenna: A type of antenna commonly used with GPS receivers. It is usually constructed of one or more (typically rectangular) elements that are photo etches on one side of double-coated printed circuit board. It is often called a patch antenna.
MID: Message Identifier (MID) is a unique number or sequence of characters that identify the protocol of a message.
MIX Antenna: A device for sending and receiving radio waves connected via an MIX plug.
MMC card: See Memory card.
mMCX Antenna: A device for sending and receiving radio waves connected via an mMCX plug.
M-Nav: Messaging and Navigation device fitted onto the dashboard of a vehicle, for two-way messaging between the vehicle and the OnlineAVL application. In addition, the device is a navigation unit able to route a driver to a location. The co-ordinates (street, road etc) of a location can be sent from the OnlineAVL application to the device in the vehicle.
MO/MT: Mobile Originated/Mobile Terminated (MO/MT). With regards to GSM telephones, calls or data generated by the mobile telephone are MO and calls or data arriving at the mobile telephone are MT.
MOB key: The Man OverBoard (MOB) key instantly marks a location on your chart so you may return to that point quickly. The mark on your chart is user-configurable in appearance.
Modem: Modulator Demodulator (Modem) is used to allow computers and terminals to send data. Older telephone line based modems used audible tones.
Modulation: A method of encoding a message signal on a carrier, which can later be decoded.
Monitor Stations: A group of worldwide stations used in the GPS control segment to monitor satellite clock and orbital parameters. The data collected is linked to a master station where corrections are calculated and made. This data is uploaded to each satellite at least once a day from an upload station.
Motorway: A limited-access road in the UK, usually consisting of three lanes for vehicles moving in both directions, intended for travelling relatively fast over long distances.
Mounting: The method(s) used for affixing a device to your boat.
Mounting kit: The supporting device for Navman GPS products consisting of several different items.
Moving Map: On a moving map, the position is always displayed at a fixed point on the screen.
MSAS: 'MTSAT' Satellite-based Augmentation System (MSAS) is a Japanese version of WAAS that covers parts of Asia and the Pacific.
MSL: Mean Sea Level (MSL).
MTBF: Mean Time Between Failure (MTBF) is an indicator of the expected reliability of a system, calculated on a statistical basis from the known rates of failure with respect to different system components. MTBF is typically expressed in hours, calculated by dividing the total number of failures by the number of hours in operation that have been observed.
Multichannel Receiver: A continuously tracking receiver that uses multiple receiver circuits to track satellites simultaneously on independent channels. Position solutions are therefore derived from simultaneous calculations of the pseudoranges.
Multipath: Signal arrival at a receiver's antenna by way of two or more different paths such as a direct, line-of-sight path and one that includes reflections off nearby objects. The difference in path lengths causes the signals to interfere at the antenna and can corrupt the receiver pseudo range and carrier-phase measurements.
Multipath Error: The errors caused by the interference of a signal by multipath.
Multiplexing: The technique used in some GPS receivers of rapidly sequencing the signals of two or more satellites through a tracking channel. This ensures navigation messages from the satellites tracked by the channel are essentially acquired simultaneously.
Multiplexing Receiver: A GPS receiver that switches at a very rapid rate between the satellites being tracked. Typically, multiplexing receivers require more time for satellite acquisition and are not as accurate as parallel channel receivers.
Multi-stop trip: A journey from A to B via C, D, E, etc.
My Home: A favourite stored on a Navman GPS navigation device; a frequently used physical address of personal importance designated by the user.

NAD-27: North American Datum of 1927. (NAD-27) is an obsolete datum of North America, dependant on an early approximation of the earth known as the Clarke Spheroid of 1866.
NAD-83: North American Datum of 1983 (NAD-83) relies on the more precise Geodetic Reference of 1980 (GRS 80).
NAGU: Notice Advisory to GLONASS Users (NAGU) is the periodic bulletin alerting GLONASS users to changes in system performance.
NANU: Notice Advisory to NAVSTAR Users (NANU) is the periodic bulletin alerting GPS users to changes in system performance.
Narrow Correlator: A correlator in a code-tracking loop in which the spacing between the early and late versions of the receiver-generated reference code is less than one chip. The use of narrow correlators results in pseudo range observations with lower noise.
Narrow Lane: The GPS observable obtained by summing the carrier-phase observations simultaneously measured, in cycles, on the L1 and L2 frequencies. The effective wavelength of the narrow-lane observable is 10.7 centimetres. The narrow-lane observable can help resolve carrier-phase ambiguities.
Nautical Mile: The unit of distance used in most maritime navigation. Based on the length of one minute of arc in the circumference of the Earth. It is 1.15 times longer than a statute mile or 6076.1 ft (1,852 metres).
NavBus: Interface to chare data between different instruments on your boat.
NAVD-88: North American Vertical Datum of 1988 (NAVD-88) is an effort by the National Geodetic Survey (NGS) to readjust the North American Vertical Datum. The NAVD-88 readjustment removes distortions from the continent wide vertical geodetic reference system.
NAVDATA: The 1500 bit navigation message broadcast by each satellite at 50 bps on both the L1 and L2 frequencies. The message contains the system time, clock correction parameters, ionospheric delay model parameters, ephemeris and health.
Navigation: The act of determining the course or heading of movement. This movement could be for a plane, ship, automobile, person on foot or any other similar means.
Navigation Message: A 37,500-bit data message included in the GPS signal by each GPS satellite. The message, sent at a rate of 50 bits per second, includes the satellite ephemeris and health, clock data and correction parameters, system time, almanac, ionospheric delay model parameters and other information about the satellites and their signals. The information is used to process GPS signals to give a user time, position and velocity. Also known as the data message.
NAVSTAR: The official US Government name given to the GPS satellite system. NAVSTAR is an acronym for NAVigational Satellite Timing And Ranging.
NED: North, East, Down (NED) is a coordinate system. See also LTP.
Network Assisted GPS: An alternative GPS solution where the receiver transmits partially processed GPS satellite data to a base station. The base station then determines the position and broadcasts the position back to the receiver. Another network assisted GPS solution is where the receiver downloads initialisation information from a base station to aid it in gaining a position fix.
NMEA: National Marine Electronics Association (NMEA) is the US standards committee that defines data message structure, contents and protocols to allow the GPS receiver to communicate with other pieces of electronic equipment aboard ships.
NMEA 0183: The committee of the National Marine Electronics Association that developed a standard for interfacing marine electronic devices. The standard communication protocol is widely used for interfacing GPS receivers and other types of navigation and marine electronics.
No entry road: A road marked by a no-entry sign that must not be entered for various reasons.
Noise: An interfering signal caused by space and atmospheric phenomena or receiver circuitry that can mask the desired signal at the receiver output.
Ns: Nanosecond (Ns) is 1 x 10 ^ (-9) seconds - one billionth of a second.
NT-Max: Electronic chart standard from C-Map
NVRAM: Non-Volatile RAM (NVRAM) is the portion of SRAM that is powered by battery backup when primary power is removed. It is used to preserve important data.

Obscuration: Term that describes the periods of time that a GPS receiver's line of sight with respect to the satellite constellation is blocked.
Observation Interval: The rate at which a receiver samples observational data from a satellite. Also: Epoch rate.
Odometer: Instrument which measures the distance travelled by a vehicle.
OEM: Original Equipment Manufacturer.
OnlineAVL: Online Automatic Vehicle Locator. OnlineAVL is a Windows based software application that runs on a customer's laptop or PC. OnlineAVL allows customers to locate, communicate with and run reports on all the vehicles in their fleet.
Operating Temperatures: The temperature range (Fahrenheit and Celsius) within which Navman products have been tested to operate with confidence.
Orthometric Height: The height of a point above the geoid.
Oscillator: A device that generates a signal of a given frequency.
OTF: "On-The-Fly" (OTF) is the term used to identify a technique that resolves differential carrier-phase integer ambiguities without requiring a GPS receiver to be stationary at any time.
Outage: The loss of availability, due to lack of visible satellites or too great a DOP (position accuracy is too unreliable).
Output Power (RMS): Power required to drive the transducer.
Over Determined Solution: The solution to a system of equations which contain more equations than the number of unknowns. GPS receivers attempt to do this whenever possible. In other words the receiver will attempt to calculate position based on 5 satellites, instead of just the 4 required for a 3d solution (latitude, longitude, altitude and receiver clock bias).

Page: A button or icon used to cycle through screens on the Navman iCN series of GPS navigation devices.
Parallel Channel Receiver: A continuously tracking receiver that uses multiple receiver circuits to track satellites simultaneously.
Parity: An extra bit at the end of a string of bits. Used in error detection, this indicates whether the number of 1s contained in the string is odd or even.
Parity Error: Exists when there is a discrepancy between a transmitted binary string's sum and the parity bit.
Passive Antenna: An antenna without an integrated low noise RF amplifier.
Patch Antenna: An antenna that consists of a thin metallic conductor bonded to a thin, grounded dielectric substrate.
PC interface: All Navman chartplotters allow data to be used on laptops or desktops via C-Map's PC Planner software (see your dealer for more information).
P-Code: Precision Code (P-Code) is the PRN code transmitted by GPS satellites sent at a rate of 10.23 MBits per second. Each satellite is assigned a unique one-week segment of the code that is reset at Saturday/Sunday midnight. The P-code is currently transmitted on both the L1 and L2 frequencies. The P-Code is typically used only used by the US military and is encrypted and reset every seven days to prevent use by unauthorised persons.
PDOP: Position DOP (PDOP) is the value expressing the relationship between the error in user position and the error in satellite position. It is proportional to 1 over the volume contained in the pyramid from the receiver to 4 satellites observed. Values of PDOP less than 3 are considered acceptable.
PDOP Mask: Upper limit for the PDOP value in which data collection and solution is suspended.
Perigee: Point in a geocentric orbit when the geometric distance is at a minimum.
Phase Angle: The time difference between the same point on two different waves, usually measured in fractions of a cycle (radians or degrees).
Phase Differencing: The technique of using different GPS receivers at different locations to measure the phase angles of the carrier signal from the same satellite. These angles are compared by a communications link between the two locations if real-time operations are required.
Phase Lock Loop: Another term for Carrier-Tracking loop.
Phase Modulation: Encoding information on a carrier signal by changing the phase so that some segments of the carrier are out of phase while others are in phase. With GPS, only two phase angles are used, 0 and 180. These represent two values, I or O.
Phase Observable: See: Reconstructed Carrier Phase.
Photogrammetry: An aerial remote sensing technique that utilises cameras and GPS. It forms the basis for many Geographic Information Systems and Land Information Systems studies.
PiN: With a lower case i: the Personal Interactive Navigation (PiN) Navman GPS navigation device.
PIN: Personal Identification Number (PIN). Navman Fleet Manager uses PINs for driver identification. Drivers can log-in to the fleet manager system using a PIN.
Ping-Rate: The number of "soundings" from your sonar per second
Pixel: Single display element on an LCD screen. More pixels enable higher resolution and detail.
Plotting scales: The range of scales available for zooming in and out of chart data.
POI: A point of interest (POI) is a specific geographical location recorded so that it can be used with the maps installed on Navman GPS navigation devices. POIs can be displayed as an icon on the Navman's map screen and also be used for route planning.
POI editor: A program for managing information about points of interest.
Point Positioning: A position calculated by multiple receivers to achieve higher accuracy than a single receiver.
Poll: Programatic or periodic check of data or sensor signals
Position: A geographic location on the earth commonly measured in latitude and longitude.
Position Fix: The GPS receiver's computed position coordinates.
Position Format: The way in which the GPS receiver displays position. Commonly the format is displayed as degrees and minutes.
Post Processed Differential GPS: The base station and receivers have no connection between then. Therefore the receivers independently record data, which will then be processed for correction at a later time, using data collected from other receivers as well.
Power Consumption: The power used by the device, expressed as Watts and/or the current in amps at a benchmark voltage as determined by the equation Watts = Volts x Amps.
PPS: Precise Positioning Service (PPS) is the full-accuracy, single-receiver GPS positioning service provided to the United States and its allied military organisations and other selected agencies. It includes access to the unencrypted P-code and the removal of SA effects. Also Pulse Per Second.
Pre-activated map: A geographic diagram that has been made usable by removing software restrictions at the factory.
Press and hold, to: To push a button or icon for three seconds.
Preview map: A computer screen displaying a geographic diagram, address details, icons and buttons.
Prime Meridian: The zero meridian (0i), used as a reference line from which longitude east and west is measured. It passes through Greenwich, England.
PRN: Pseudorandom Noise (PRN) is a sequence of digital bits that appear to be randomly distributed, but which can be reproduced. Each NAVSTAR satellite has its own unique C/A and P pseudo random noise codes.
PRN Code: Pseudorandom Noise (PRN) Code is the deterministic binary sequences with noise-like properties. Also called pseudo-noise codes. These codes are used in spread-spectrum communications systems and in ranging systems such as GPS. GPS satellites transmit two PRN codes: the C/A-code and P-code. In GPS it is the identifying signature signal transmitted by each GPS satellite and mirrored by the GPS receiver in order to separate and retrieve the signal from background noise.
Pseudolite: A ground based transmitter that mimics a GPS signal. These devices can be used around airports for such tasks as precision instrument landings.
Pseudorange: The range between the antenna phase centres of a GPS satellite and a GPS receiver, measured by the receiver's delay-lock loop using either the C/A or P-code. The range is biased by the offset of the clock in the receiver from that in the satellite and by atmospheric propagation delays. It is measured by using the uncorrected time comparisons from the satellite transmitted code and the local receiver reference code.
Pseudorange Difference: See: Reconstructed Carrier Phase.
PVT: Position, Velocity, Time (PVT).

Quadrifilar Helix: A type of circularly polarised antenna used with some GPS receivers. The antenna consists of two orthogonal, fractional-turn bifilar wire or metal strip helices fed in phase quadrature. It is also known as a volute antenna.
Quasi Zenith Satellite System: Multi-function satellite system, able to provide communication, broadcasting and positioning services to users in a specified region from a high elevation angle. This region is usually one plagued by the inability to receive low angle satellites.
QVGA: Refers to the number of pixels on your screen. QVGA represents 320x240 pixels.