Glossary

A/D: Analogue to Digital (A/D) refers to the conversion from analogy 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.

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