a b c d e f g h i j k l m n o p q r s t u v w x y z
A two-dimensional GPS position fix that includes only horizontal coordinates, no elevation. It requires a minimum of three visible satellites.
A three-dimensional GPS position fix that includes horizontal coordinates, plus elevation. It requires a minimum of four visible satellites.
A mode in which a position is identified with respect to a well-defined coordinate system, commonly a geocentric system (i.e., a system whose point of origin coincides with the center of mass of the earth).
The degree of closeness of a measurement result to its true value. The degree of conformance between the estimated or measured position, time, and/or velocity of a GPS receiver and its true time, position, and/or velocity as compared with a constant standard. Radio navigation system accuracy is usually presented as a statistical measure of system error.
The accuracy with which a user can measure position relative to that of another user of the same navigation system at the same time.
The industry standard definition of static accuracy is the standard deviation of error if a point set by a receiver was tested in a fix position for 24 hours.
The transmission of a short packet from the receiving device to the sending device to indicate that the data sent has been received error.
The ability to find and lock on to satellite signals for ranging.
The time it takes a GPS receiver to acquire satellite signals and determine the initial position.
An antenna that amplifies the GPS signal before sending it to the receiver.
Active systems utilize wireless networks that allow you to receive data from all of the vehicles in your fleet, and view the location of any or all of your vehicles in near “real-time”.
Active Vehicle Tracking
GPS Vehicle Tracking system that includes a mobile radio as part of the systems. An Active system collects the GPS information using an onboard GPS receiver and then transmits selected data to a server over a cellular network such as Mobitex or GPS.
Additional Secondary Factor (ASF)
Error propagation time caused by radio waves slowing down as they pass over different terrain. This is in addition to slowing down as radio waves pass over sea water Error propagation time caused by radio waves slowing down as they pass over different terrain.
Advanced Intelligent Networks. Refers to networks that route calls based on database information that can affect the inbound and outbound flow of the call.
Actual time spent talking on the wireless telephone. Most carriers bill customers based on how many minutes of air time they use each month. The more minutes of time spent talking on the phone, the higher the bill.
Notifications that are customized and automatically sent via email, pager, phone, or other electronic delivery to notify managers of unusual or undesirable activity.
A special method used to solve a certain type of mathematical problem.
A data file that contains orbit information on all satellites, clock corrections, and atmospheric delay parameters. It is transmitted by a GPS satellite to a GPS receiver, where it facilitates rapid satellite vehicle acquisition within GPS receivers. Almanac data must be acquired before GPS navigation can begin.
A message or other type of readout containing both letters ('alphas') and numbers ('numerics'). Regarding wireless, 'alphanumeric memory dial' is a special type of dial.
An instrument that measures altitude or elevation with respect to a reference level, usually mean sea level, by means of air pressure.
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 onto 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.
Height of a radio wave as measured from an imaginary center line to the wave peak.
Amplitude Modulation (AM)
A method of encoding a message on the carrier signal by altering the height of the signal while keeping its frequency constant.
The traditional method of modulating radio signals so that they can carry information. AM (amplitude modulation) and FM (frequency modulation) are the two most common methods of analog modulation. The principal feature of analog signals is that they are continuous. In contrast, digital signals consist of values measured at discrete intervals.
A device for transmitting and/or receiving signals. The size and shape of antennas are determined, in large part, by the frequency of the signal they are receiving. In a GPS system, there are two antennas.
Encryption of the P-code to protect the P-signals from being "spoofed" through the transmission of false GPS signals by an adversary.
The ability of a receiver to start position calculations without being given an approximate location and approximate time.
A GPS System that enables one to track an asset / vehicle using several technologies including a GPS receiver.
A very precise clock that operates using the elements cesium or rubidium. A cesium clock has an error of one second per million years. GPS satellites contain multiple cesium and rubidium clocks.
A process used by the wireless carriers to verify the identity of a mobile station.
Automatic Vehicle Location (AVL)
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. A technology consisting of hardware and software that is installed on vehicles and is used to pinpoint the location of a vehicle to within a few meters.
Automatic Vehicle Monitoring (AVM)
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.
The number of hours per day that a particular location has sufficient satellites to make a GPS position fix.
This is the direction of a celestial object, measured clockwise around the observer's horizon from north. So an object due north has an azimuth of 0°, one due east 90°, south 180° and west 270°. Azimuth and altitude are usually used together to give the direction of an object in the top centric coordinate system.
A relative range of frequencies that can carry a signal without distortion on a transmission medium.
Also called a reference station. A receiver that is set up on a known location specifically to collect data for differentially correcting rover files. The base station calculates the error for each satellite and, through differential correction, improves the accuracy of GPS positions collected at unknown locations by a roving GPS receiver.
The difference in three dimensional coordinates (X, Y, Z) computed from the difference in simultaneous carrier phase observations at two or more receivers.
Stationary transmitter that emits signals in all directions (also called a non-directional beacon). In DGPS, the beacon transmitter also broadcasts pseudo range correction data to nearby GPS receivers for greater accuracy.
The compass direction from a position to a destination, measured to the nearest degree (also call an azimuth). In a GPS receiver, bearing usually refers to the direction to a waypoint.
A relatively permanent material object, natural or man-made, with a known elevation. A bench mark can be used as a reference point when navigating a route or in determining the elevation of nearby land features.
Binary Biphase 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)
A unit of information in an electronic system expressed as a choice between two possible values, for example, 0 or 1.
Term referring to the Federal Geodetic Control Subcommittee publication "Input Formats and Specifications of the National Geodetic Survey Data Base" which defines the file formats for data submission to the National Geodetic Reference System.
Bits Per Second. The unit of measurement for the rate at which data is transmitted.
Basic Trading Area. A service area designed by Rand McNally and adopted by the FCC to promote the rapid deployment and ubiquitous coverage of Personal Communications Services (PCS). Built from county boundaries, BTAs generally cover a city and its surrounding environs. BTAs are component parts of Major Trading Areas (MTAs). There are 493 BTAs in the United States.
The standard (Course/Acquisition) GPS code. A sequence of 1023 pseudo-random, binary, biphase modulations on the GPS carrier at a chip rate of 1.023 MHz. Also known as the "civilian code" or S-code. The less accurate Civilian GPS Signal. 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, and is accurate to 100 meters or better.
Common Air Interface. A standard for the interface between a radio network and equipment. A CAI allows multiple vendors to develop equipment that will interoperate.
Each amateur radio station is assigned a call sign by the government of that country which allows the operator to transmit in the amateur radio bands.
The frequency of the unmodulated fundamental output of a radio transmitter. The GPS L1 carrier frequency is 1575.42 MHz.
GPS measurements based on the L1 or L2 carrier signal.
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)
The ratio of the power level of a signal carrier to the noise power in a 1-Hz bandwidth. This is a key parameter in the analysis of GPS receiver performance. Nominal GPS receiver C/N0 values often are in the 40 to 50-dB-Hz range.
A module in a GPS receiver that demodulates, or extracts, the satellite message by aligning the phase of the receiver's local oscillator signal with the phase of the frequency-shifted, received carrier. Once the local oscillator signal is locked to the carrier, its phase can be measured to provide the carrier-phase observation.
The art or technique of making maps or charts. Many GPS receivers have detailed mapping—or cartography—capabilities.
A channel of a GPS receiver consists of the circuitry necessary to receive the signal from a single GPS satellite.
Binary elements or digits that, unlike bits, convey no information. A PRN code consists of a sequence of chips.
A switching technique that establishes a dedicated and uninterrupted connection between the sender and the receiver.
Circular Error Probable (CEP)
A statistical measure of the horizontal precision. The CEP value is defined as a circle of a specified radii that encloses 50% of the data points.
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.
The difference between the indicated clock time in the GPS receiver and true universal time.
A constant difference in the time reading between two clocks, normally used to indicate a difference between two time zones.
Commercial Mobile Radio Service. The regulatory classification that the FCC uses to govern all commercial wireless service providers, including Personal Communications Services, cellular, and Enhanced Specialized Mobile Radio.
Code Division Multile Access (CDMA)
A technique of multiplexing, also called spread spectrum, in which analog signals are converted into digital form for transmission. For each communication channel, the signals are encoded in a sequence known to the transmitter and the receiver for that channel.
Code Division Multiple Access (CDMA)
A method whereby many radios use the same frequency, but each one has a unique code. GPS uses CDMA techniques with codes for their unique cross-correlation properties.
Code phase GPS
GPS measurements based on the pseudo random code (C/A or P) as opposed to the carrier of that code.
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.
The ability of a GPS receiver to start providing position updates without the assistance of any almanac information stored in its memory.
Reducing the size of data to be stored or transmitted in order to save transmission time, capacity, or storage space.
Refers to either the specific set of satellites used in calculating positions or all the satellites visible to a GPS receiver at one time.
Continuous Kinematic Surveying
Successive baseline solutions generated at every epoch of an unbroken observation set. Typically used to track a vehicle or platform in motion.
A line on a map that connects points of equal elevation.
Also called a control station. The National Geodetic Survey maintains a nation-wide set of control points. A world-wide network of GPS monitoring and control stations that ensure the accuracy of satellite positions and their clocks.
A worldwide chain of monitoring and control stations that control and manage the GPS satellite constellation.
Coordinated Universal Time (UTC)
Replaced Greenwich Mean Time (GMT) as the world standard for time in 1986. UTC uses atomic clock measurements to add or omit leap seconds each year to compensate for changes in the rotation of the earth.
A set of numbers that describes your location on or above the earth. Coordinates are typically based on latitude/longitude lines of reference or a global/regional grid projection (e.g., UTM, MGRS, Maidenhead).
The extent to which one observation or computed value is influenced by the change in an other, or that both are influenced by a third. The correlation coefficient is the proportion of the total variation in the dependent variable (y) which can be attributed to the relationship with the independent variable (x).
Continuously Operating Reference Station Fixed GPS receiver site in continuous operation.
The direction from the beginning landmark of a course to its destination (measured in degrees, radians, or mils), or the direction from a route waypoint to the next waypoint in the route segment.
Course Deviation Indicator (CDI)
A technique for displaying the amount and direction of crosstrack error (XTE).
Course Made Good (CMG)
The bearing from the starting point to the present position.
Course Made Good (CMG)
The bearing from the 'active from' position (your starting point) to your present position.
Course Over Ground (COG)
Your direction of movement relative to a ground position.
Course To Steer
The heading you need to maintain in order to reach a destination.
Course Up Orientation
Fixes the GPS receiver's map display so the direction of navigation is always "up."
Cross-Track Error (XTE)
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
Crosstrack Error (XTE/XTK)
The distance you are off the desired course in either direction.
Course to Steer
Closed User Group. Selected user groups that communicate freely within the group, but have restricted incoming, and often outgoing, communications.
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 may 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.
A 1500 bit message included in the GPS signal which reports the satellite's location, clock corrections, and health.
A handheld, lightweight data entry computer. It can be used to store additional data obtained by a GPS receiver.
A math model which depicts a part of the surface of the earth. Latitude and longitude lines on a paper map are referenced to a specific map datum. The map datum selected on a GPS receiver needs to match the datum listed on the corresponding paper map in order for position readings to match.
Differential Beacon Receivers tune to the United States Coast Guard's high differential correction beacon stations for improved position accuracy. RTCM 104 input signal is supplied to a DGPS unit to correct for SA and Atmospheric errors. The operating frequency range is 285 kilohertz to 325 kilohertz.
Dynamic Data Exchange. A Windows protocol that allows communication between applications. When information is updated in one application, related information will be updated in other applications.
A very simple method of using time and distance to navigate. Distance traveled is determined by multiplying speed by elapsed time.
Deflection of the vertical
The angle at a point on the surface of the earth between the vertical at that point (the line normal to the geoid) and the line through the point which is normal to the reference ellipse.
Degrees of freedom
The number of observations minus the minimum number required to uniquely define the figure.
Another term for a code-tracking loop.
Separating coded data from the carrier signal.
Desired Track (DTK)
The compass course between the "from" and "to" waypoints.
Errors from your course. Either built in or unintentional. One type of deviation is Magnetic, the difference between a true course and what a compass shows.
Differential GPS (DGPS)
A technique to improve GPS accuracy that uses pseudorange errors measured at a known location to improve the measurements made by other GPS receivers within the same general geographic area. One to ten meter accuracy is typical, possible: <1 cm. An extension of the GPS system that uses land-based radio beacons to transmit position corrections to GPS receivers. DGPS reduces the effect of selective availability, propagation delay, etc. and can improve position accuracy to better than 10 meters.
A method of encoding information for transmission. Information (in most cases a voice conversation) is turned into a series of digital bits.
Digital Raster Graphic (DRG)
The United States Geological Survey is releasing digital versions of all of the topographic maps. These files are called Digital Raster Graphics (DRG) maps. The images themselves are stored in a format called GeoTiff
Dilution Of Precision (DOP)
A measure of the GPS receiver/satellite geometry. A low DOP value indicates better relative geometry and higher corresponding accuracy. The DOP indicators are GDOP (geometric DOP), PDOP (position DOP), HDOP (horizontal DOP), VDOP (vertical DOP), and TDOP (time clock offset).
The length (in feet, meters, miles, etc.) between two waypoints or from your current position to a destination waypoint. This length can be measured in straight-line (rhumb line) or great-circle (over the earth) terms. GPS normally uses great circle calculations for distance and desired track.
Distance Root Mean Square (DRMS)
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.
The introduction of digital noise. This is the process the US Department of Defense (DoD) uses to add inaccuracy to GPS signals to induce Selective Availability.
A signal processing strategy that uses a measured doppler shift to help the receiver smoothly track the GPS signal. Allows more precise velocity and position measurement.
The apparent change in the frequency of a signal caused by the relative motion of the transmitter and receiver.
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.
A transmission path for the communication of signals and data from a communications satellite or other space vehicle to the earth.
Digital Signal Processor. A specialized computer chip that performs calculations on digitized signals that were originally analog and then sends the results.
Dynamic positioning or kinematic positioning refers to applications in which the position of a moving object is determined.
Earth Centered Earth Fixed rectangular coordinate system (Cartesian coordinates), where the positive X axis lies on the equatorial plane passing through the prime meridian (Greenwich), the positive Y axis lies on the equatorial plane at 90 east, and positive Z passes north through the mean rotational axis of the earth.
The continuous distribution of energy in the form of electromagnetic waves, which are arranged in order of their frequencies or wavelengths.
Electronic Vehicle Tracking
A technology consisting of hardware and software that is installed on vehicles and is used to pinpoint the location of a vehicle to within a few meters.
The distance above or below mean sea level.
A geometric surface, all of whose plane sections are either ellipses or circles.
The distance from a point to the reference ellipsoid along a line normal to the ellipsoid.
Electromagnetic Compatibility. The ability of equipment or systems to be used in their intended environment within designed efficiency levels without causing or receiving degradation due to unintentional electromagnetic interference. Proper shielding of devices reduces interference.
The transformation of data, for the purpose of privacy, into an unreadable format until reformatted with a decryption key. 'Public key' encryption utilizes the RSA (which stands for its developers, Rivest, Shamir, and Adleman) encryption key. PGP, or Pretty Good Privacy, is a cryptography program for computer data.
Estimated Position Error. How much the unit thinks it is off target.
Current satellite position and timing information transmitted as part of the satellite data message. A set of ephemeris data is valid for several hours.
Errors which originate in the ephemeris data transmitted by a GPS satellite. Ephemeris errors are removed by differential correction.
A specific instant in time. GPS carrier phase measurements are made at a given frequency (e.g. every 30 seconds) or epoch rate.
Zero degrees Latitude. A line around the center of earth 24,901.55 miles (40,075.16 kilometers) long.
A set of individual error sources with statements of the percentage of the total system error contributed by each source.
A statistical measure of the positional error at a given point computed from the propagation of all errors contributing to the position.
Electronic Serial Number. The unique number assigned to a wireless device by the manufacturer. According to the Federal Communications Commission, the ESN is to be fixed and unchangeable.
Estimated Position Error (EPE)
A measurement of horizontal position error in feet or meters based upon a variety of factors including DOP and satellite signal quality.
Estimated Time Enroute (ETE)
The time it will take to reach your destination (in hours/minutes or minutes/seconds) based upon your present position, speed, and course.
Estimated Time Of Arrival (ETA)
The estimated time you will arrive at a destination.
Extended Total Access Communications Systems. The conventional wireless technology used in the United Kingdom and other countries. It was developed from the U.S. AMPS technology.
Fast switching channel
A single channel which rapidly samples a number of satellite ranges. Switching time is sufficiently fast (2 to 5 milliseconds) to recover the data message.
Frequency Division Multiple Access. Method of radio transmission that allows multiple users to access a group of radio frequency bands without interference.
Frequency Hopping Spread Spectrum. A technique used in spread spectrum radio transmission systems, such as wireless LANs and some PCS cellular systems that involve the conversion of a data stream into a stream of packets.
A position that is determined by the navigation unit (consisting of latitude, longitude (or grid position), altitude, time, and date).
A technology consisting of hardware and software that is installed on fleet vehicles and is used to pinpoint the location of a vehicle to within a few meters.
Fleet Management Tracking
A technology consisting of hardware and software that is installed on fleet vehicles and is used to pinpoint the location of a vehicle to within a few meters. Fleet Tracking systems usually include a wide variety of reports and alerts to notify managers of unusual or undesirable vehicle activity.
The number of waves passing a specific point within a unit period of time, expressed in Hertz (cycles per second).
A particular range of frequencies.
Frequency Modulation (FM)
A method of encoding information about a carrier signal by altering the frequency while amplitude remains constant.
The distribution of signal amplitudes as a function of frequency.
Geometric Dilution of Precision, see DOP. GDOP Components(see): HDOP, PDOP, TDOP, VDOP.
A high-tech version of hide-and-seek. Geocachers seek out hidden treasures utilizing GPS coordinates posted on the Internet by those hiding the cache.
The branch of applied mathematics that deals with the measurement, curvature, and shape of the earth.
Geographic, or pertaining to geodesy. Latitude and longitude readings are geodetic coordinates.
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 center with respect to the earth's center 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. A math model representing the size and shape of the earth (or a portion of it).
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.
Global surveys done to establish control networks as a basis for accurate land mapping.
Geographic Information System (GIS)
A computer system or software capable of assembling, storing, manipulating, and displaying geographically referenced information (i.e., data identified according to their location). In practical use, GIS often refers to the computer system, software, and the data collection equipment, personnel, and actual data.
The undulating, but smooth, equipotential surface (a surface of equal gravity potential) of the earth's gravity field, which coincides most closely with mean sea level. The geoid is the primary reference surface for heights.
Geometric Dilution of Precision (GDOP)
The effects of the combined errors of four variables (latitude, longitude, altitude, and time) on the accuracy of a three-dimensional fix.
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.
A specific orbit around where a satellite rotates around the earth at the same rotational speed as the earth. A satellite rotating in geosynchronous orbit appears to remain stationary when viewed from a point on or near the equator. It is also referred to as a geostationary orbit.
Gigahertz Billions of Hertz. Personal Communications Services operate in the 1.9 GHz band of the electromagnetic spectrum. See also Hertz, KHz, and MHz.
Geographic Information System. A computer based system that is capable of collecting, managing and analyzing geographic spatial data.
A data sentence that is part of the NMEA protocol for transferring information between electronic devices. The GLL sentence contains position information.
Global Navigation Satellite System (GLONASS)
The Russian satellite navigation system. GLONASS provides worldwide coverage, however, its accuracy performance optimized for the northern latitudes.
Global Positioning System (GPS)
A global navigation system that is based on triangulation from a constellation of 24 satellites orbiting the earth. A GPS receiver pinpoints its position on earth by measuring its distance from the satellites. It does so by calculating the time it takes for a coded radio message to pass from the satellite to the GPS unit. A GPS unit needs at least three measurements to determine its exact position.
A route consisting of one leg, with your present position being the start of the route and a single defined waypoint as the destination.
See Global Positioning System.
GPS Fleet Management
A term most commonly used to describe a product and service for locating, monitoring, and managing vehicle fleets.
GPS System Time
The time scale to which GPS signals are referenced. GPS Time derives from a composite or paper clock consisting of all operational monitor station and satellite atomic clocks. It is steered over the long run to keep it within about 1 micro-second of UTC, as maintained by the Master Clock at the U.S. Naval Observatory, ignoring the UTC leap seconds.
Incremental number of weeks, starting at 0 hour UTC on the date January 6, 1980. April 6, 1997 is the first day of GPS week 900.
A block or area of blocks within the gravity measurement database without observations. A geoid model relying upon this database would be weak and possibly in error at these blocks.
The intersection of a plane through the center of the Earth and the surface of the Earth. The shortest distance between two points on the Earth is a great circle route. All longitudes are great circles. The only latitude that is a great circle is the Equator.
Greenwich Mean Time (GMT)
The mean solar time for Greenwich, England, which is located on the Prime Meridian (zero longitude). Based on the rotation of the earth, GMT is used as the basis for calculating standard time throughout most of the world.
A pattern of regularly spaced horizontal and vertical lines forming square zones on a map used as a reference for establishing points. Grid examples are UTM, MGRS, and Maidenhead.
The velocity you are traveling relative to a ground position.
A radiowave that travels along the earth's surface.
The reference ellipsoid of the NAD83 coordinate system.
Global System for Mobile Communications. A world standard for digital wireless transmissions. GSM is the most widely used standard in the world today with more than 150 million users worldwide. See also TDMA.
Geosynchronous Satellite Orbit. A satellite in orbit 23,000 miles over the equator with an orbit time of 24 hours. Also known as geostationary.
Graphical User Interface. A name for any computer interface that substitutes graphics for characters.
Hand-Over Word (HOW)
The second word in each subframe of the navigation message. It contains the Z-count at the leading edge of the next subframe and is used by a GPS receiver to determine where in its generated P-code to start the correlation search process.
The word in the GPS message that contains synchronization information for the transfer of tracking from the C/A to P code.
Handheld Device Markup Language. A modification of standard HTML, developed by Unwired Planet, for use on small screens of mobile phones, PDAs, and pagers. HDML is a text.
The direction in which a vehicle is moving. For air and sea operations, this may differ from actual Course Over Ground (COG) due to winds, currents, etc.
A term used when an orbiting GPS satellite is suitable for use. "State" is also used to refer to satellite health.
An accuracy enhancement technique in which the known height of the receiver is entered into the navigation solution, which in effect provides another satellite's range.
A measurement of electromagnetic energy, equivalent to one 'wave' or cycle per second. See also KHz, MHz, and GHz.
High Frequency (HF)
Radio frequencies in the band from 3 to 30 MHz.
Horizontal Dilution of Precision (HDOP)
The effects on accuracy of the combined errors in a two-dimensional fix obtained from crossing two lines of position
Horizontal Time Dependent Positioning model A computer database and interpolation program to predict horizontal displacements between coordinate points over time.
Hypertext Markup Language. An authoring software language used on the Web. HTML is used to create Web pages and hyperlinks.
Hypertext Transfer Protocol. The protocol used by the Web server and the client browser to communicate and move documents around the Internet.
The signal coming from the GPS Satellites.
International Mobile Station Identifier. A number assigned to a mobile station by the wireless carrier uniquely identifying the mobile station nationally and internationally.
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.
A band of the electromagnetic spectrum used for airwave communications and some fiber.
Entering such data as time, time off-set, approximate position, and antenna height into a receiver (cold start with no almanac) to help the unit find and track satellites.
An international consortium chartered in the mid-1970s to provide improved maritime public correspondence and radio determination capabilities.
The two-way transfer of GPS information with another device, such as a nav plotter, autopilot, or another GPS unit.
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.
The routing of telecommunications traffic between the networks of different communications companies.
Any distortion of the transmitted signal that impedes the reception of the signal at the receiver.
A variation of phase differencing in which two different antennas sample the GPS signal wavefront at two locations and then feed the information into a single amplifier and interferometer (mixer) in which phase difference observations are made.
To display and navigate a route from end to beginning for purposes of returning to the route's starting point.
The process by which atoms form electrically charged particles called ions.
A region of the earth's atmosphere where ionization caused by incoming solar radiation affects the transmission of GPS radio waves. It extends from a height of 50 kilometers (30 miles) to 400 kilometers (250 miles) above the surface.
Signal delay or acceleration as a wave propagates through the ionosphere. Phase delay depends upon the electron content and affects the carrier signal. Group delay depends upon the dispersion in the ionosphere as well, and affects the code signal.
The change in the propagation speed of a signal as it passes through the ionosphere.
A line on a map or chart where the magnetic deviation is the same.
International Telecommunication Union
A programming language from Sun Microsystems which abstracts data on byte codes so that the same code runs on any operating system. Java software is generally posted on the Web and downloadable over the Internet to a PC. HotJava is installed on a Web browser and enables Java programs to be delivered over the Web and run on a PC.
An optimum mathematical procedure for recursively estimating dynamically changing parameters, such as the position and velocity of a vessel, from noise-contaminated observations.
A set of six parameters that describe the position and velocity of a satellite in a purely elliptical (Keplerian) orbit. These parameters are the semi major axis and 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.
Kilohertz Thousands of Hertz. Each wireless phone call occupies only a few Kilohertz. See also Hertz, MHz, and GHz.
A radio signal that has 1,000 cycles per second.
Observations while a receiver is in motion. In surveying applications, kinematic refers to uninterrupted carrier.
Positioning a continuously moving platform by using GPS carrier-phase data while operating in a differential mode.
A precision differential GPS surveying technique in which the roving user does not need to stop to collect precision information. Meter to centimeter-level accuracy is available using mode, dual-frequency, carrier-phase measurement techniques.
The group of radio frequencies extending from 390 MHz to 1550 MHz. The GPS carrier frequencies L1 (15735 MHz) and L2 (1227.6 MHz) are in the L-band.
One of the two radio frequencies transmitted by the GPS satellites. This frequency carries the Coarse Acquisition Code (C/A code), P-Code, and the nav message, and is transmitted on a frequency of 1575.42 MHz.
One of the two radio frequencies transmitted by the GPS satellites. This frequency carries only the P-Code, and is transmitted on a frequency of 1227.6 MHz.
Local Area Network. A data communications network, typically within a building or campus, to link computers and peripheral devices under some form of standard control.
A position's distance north or south of the equator, measured by degrees from zero to 90. One minute of latitude equals one nautical mile.
Local Differential GPS. Two or more GPS Receivers are used to create a local reference to each other.
A portion of a route consisting of a starting (from) waypoint and a destination (to) waypoint. A route that is comprised of waypoints A, B, C, and D would contain three legs. The route legs would be from A to B, from B to C, and from C to D.
Low Earth Orbit. An orbital plane a few hundred miles above the earth. A new generation of communications satellites is being launched in this orbit. LEO satellites are generally divided into two groups: big and little LEOs, with each group assigned specific radio frequencies. Big LEOs support both voice and data communications while little LEOs support only data communications.
Line of Position (LOP)
Locus Of Points have a constant measurement (such as range, range difference). A fix is determined by crossing two lines of position.
Line Of Sight (LOS) Propagation
Of an electromagnetic wave, propagation in which the direct transmission path from the transmitter to the receiver is unobstructed. The need for LOS propagation is most critical at GPS frequencies.
Local Multipoint Distribution System. A system developed by Bellcore for Wireless Local Loop (WLL) applications. In the U.S., the FCC set aside a total LMDS bandwidth of 1.15 GHz in the 28.
Local-Area Augmentation System (LAAS)
A system similar to WAAS, in that similar correction data are used. But in this case, the correction data are transmitted from a local source, typically at an airport or another location where accurate positioning is needed. These correction data are typically useful for only about a thirty to fifty kilometer radius around the transmitter.
The angular measurement of a point on the earth's surface, east or west of the prime meridian. The prime meridian runs through Greenwich, England and is 0 degrees longitude. Since measurements are made East and West, the maximum longitude value is 180 degrees. Mathematically, longitudes are usually denoted as positive for easterly longitudes (e.g., 71 degrees = 71 E), and negative for westerly longitudes (e.g., -65 degrees = 65 W).
Loran, which stands for LOng RAnge Navigation, is a grid of radio waves in many areas of the globe that allows accurate position plotting. Loran transmitting stations around the globe continually transmit 100 kHz radio signals. Special shipboard Loran receivers interpret these signals and provide readings that correspond to a grid overprinted on nautical charts. By comparing signals from two different stations, the mariner uses the grid to determine the position of the vessel.
Represents the direction of the north magnetic pole from the observer's position. The direction a compass points.
The different between true North (pointing towards the Geographic Pole) and Magnetic North (pointing towards Magnetic Pole) where a compass points to. The magnetic variation of the earth changes at a rate of 50.27 seconds of arc per year.
Mobitex Access Number. This is the access number for Mobitex networks to identify wireless data radios. In addition to the MAN number, there is also an Electronic Serial Number that is used to verify if the transmission is for the intended receiver. MAN numbers are 8 digits in length.
What reference map is used in determining the Fixes.
A graphic representation of a geographic area and its features.
The systematic arrangement of the earth's spherical or geographic coordinate system onto a plane; the process of transforming a globe into a flat map with the least amount of distortion; a transformation process.
Cut off angle The point above the observer's horizon below which satellite signals are no longer tracked and/or processed. 10° to 25° is typical.
Antenna connector used on some of the newer GPS units.
Mean Sea Level
The average level of the ocean's surface, as measured by the level halfway between mean high and low tide. Used as a standard in determining land elevation or sea depths.
One million cycles per second. Used to describe a radio frequency.
An imaginary line that circles the earth, passing through the geographic poles and any given point on the earth's surface. All points on a given meridian have the same longitude.
A light or other indicator on a wireless phone that notifies a user that a call has come in. A useful feature especially if the wireless subscriber has voice mail.
Military Grid Reference System. The MGRS is an alphanumeric version of a numerical UTM (Universal Transverse Mercator) or UPS (Universal Polar Stereographic) grid coordinate.
Megahertz. Millions of Hertz Cellular and ESMR systems operate in the 800 and 900 MHz bands of the electromagnetic spectrum. See also Hertz, KHz, and GHz.
A type of antenna commonly used with GPS receivers. It is usually constructed of one or more (typically rectangular) elements that are photoetched on one side of double-coated, printed-circuit board.
Multipurpose Internet Mail Extensions. The standard format, developed and adopted by the Internet Engineering Task Force (IETF).
A method of encoding a message signal on top of a carrier, which can be decoded at a later time.
Mobile Satellite Service. Communications transmission service provided by satellites. A single satellite can provide coverage to the entire United States.
Major Trading Area. A service area designed by Rand McNally and adopted by the FCC to promote the rapid deployment and ubiquitous coverage of Personal Communications Services (PCS). Built from Basic Trading Areas (BTAs), MTAs are centered on a major city and generally cover an area the size of a state. There are 51 MTAs in the United States.
Mobile Telephone Switching Office. The central computer that connects a wireless phone call to the public telephone network.
A GPS receiver that can simultaneously track more than one satellite signal.
An error caused when a satellite signal reaches the GPS receiver antenna by more than one path. Usually caused by one or more paths being bounced or reflected. The TV equivalent of multipath is "ghosting."
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.
A channel of a GPS receiver that can be sequenced through a number of satellite signals.
A GPS receiver that switches at a very rapid rate between satellites being tracked. Typically, multiplexing receivers require more time for satellite acquisition and are not as accurate as parallel channel receivers. Multiplexing receivers are also more prone to lose a satellite fix in dense woods than parallel channel GPS receivers.
Horizontal coordinate system for U.S., Canada and Mexico. Originally published in 1986 it is based upon the GRS 80 ellipsoid with its origin at the center of mass defined by BIH at epoch 1984.0. Geodetic surveyors must be particularly cognizant of epoch dates attached to the NAD 83 an acronym. These refer to the mean date of the observations used in the regional adjustment.
North American Datum 1927. It is broken down into different areas, from Central America to Greenland.
Number Assignment Module. The NAM is the electronic memory in the wireless phone that stores the telephone number and electronic serial number.
Notice Advisory to NAVSTAR Users. A periodic bulletin alerting GPS users to changes in system performance.
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 pseudorange observations with lower noise.
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 centimeters. The narrow-lane observable can help resolve carrier-phase ambiguities.
A unit of length used in sea and air navigation, based on the length of one minute of arc of a great circle, especially an international and U.S. unit equal to 1,852 meters (about 6,076 feet).
Vertical (elevation) reference system for U.S., Canada and Mexico. Published in 1991 the orthometric heights are derived from an adjustment of leveling data constrained at a single point on the St. Lawrence Seaway.
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.
The message transmitted by each GPS satellite containing system time, clock correction parameters, ionospheric delay model parameters, and the satellite’s ephemeris data and health. The information is used to process GPS signals to give the user time, position, and velocity. Also known as the data message.
National Imaging and Mapping Agency.
An interfering signal that tends to mask the desired signal at the receiver output and which can be caused by space and atmospheric phenomena, can be human made, or can be caused by receiver circuitry.
North Up Orientation
Fixes the GPS receiver’s map display so north is always fixed at the top of the screen.
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.
The height of a point above the geoid.
A device that generates a signal of a given frequency.
The Precise or Protected code. A very long sequence of pseudo-random binary biphase modulations on the GPS carrier at a chip rate of 10.23 MHz, which repeats about every 267 days. Each 1-week segment of this code is unique to one GPS satellite and is reset each week.
A bundle of data organized in a specific way for transmission. The three principal elements of a packet include the header, the text, and the trailer (error detection and correction bits).
Radio transmitted message system.
The transmission of data over radio using a version of the X.25 data communications protocol. The data is broken into packets and transmitted wirelessly.
Parallel Channel Receiver
A continuous tracking receiver using multiple receiver circuits to track more than one satellite simultaneously.
An extra bit at the end of a string of bits. Used in error detection, this reveals whether the number of 1s is odd or even.
Passive units are installed in a vehicle, and the data on the device is manually downloaded from the vehicle at the end of the day.
Also called repeatability. In the context of parallel tracking, this is how far off you are from one path to the next, regardless on which pass you are on. Mostly the pass-to-pass accuracy is approximately 2 to 3 times more precise then the statistic accuracy.
The time difference between the same point on two different waves, usually measured in fractions of a cycle (radians or degrees).
The apparent center of signal reception at an antenna. The phase center of an antenna is not constant but is dependent upon the observation angle and the signal frequency.
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.
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, representing the two values, I or O.
An exact, unique location based on a geographic coordinate system.
The GPS receiver's computed position coordinates.
The way in which the GPS receiver's position will be displayed on the screen. Commonly displayed as latitude/longitude in degrees and minutes, with options for degrees, minutes and seconds, degrees only, or one of several grid formats.
Precise Positioning Service (PPS)
The full-accuracy, single-receiver GPS positioning service provided to the United States and its allied military organizations and other selected agencies. It includes access to the unencrypted P-code and the removal of SA effects.
The degree of repeatability that repeated measurements of the same quantity display, and is therefore a means of describing the quality of the data with respect to random errors. Precision is traditionally measured using the standard deviation.
The zero meridian, used as a reference line from which longitude east and west is measured. It passes through Greenwich, England.
A specific set of rules for organizing the transmission of data in a network.
A ground-based differential GPS, installed on the ground in the local area. It is used to supply "illumination" and correction signals for DGPS systems.
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.
Pseudo-random noise (PRN)
A sequence of digital 1's and 0's that appear to be randomly distributed like noise but that can be reproduced exactly. Their most important property is a low autocorrelation value for all delays or lags except when they coincide exactly. Each GPS satellite has unique C/A and P pseudorandom-noise codes.
The measured distance between the GPS receiver and the GPS satellite using uncorrected time comparisons from satellite-transmitted code and the local receiver's reference code.
Radio Direction Finder
A radio receiver that features a directional antenna and a visual null indicator for use in determining lines of position from radiobeacons at known positions.
Radio Frequency (RF)
Radio frequency refers to a signal generated by a radio transmitter and sent out through an antenna. The frequency of the transmission is described in terms of the number of cycles per second or Hertz (Hz). A radio would be tuned to this frequency in order to receive the transmission. A radio signal is sometimes referred to by its initials, "RF".
Receiver Autonomous Integrity Monitoring; A GPS receiver system that would allow the receiver to detect incorrect signals being transmitted by the satellites by comparing solutions with different sets of satellites.
A fixed distance between two points, such as between a starting and an ending waypoint or a satellite and a GPS receiver.
A technique used to determine a line of position by calculating the distance between a receiver and a known reference point.
Real Time Tracking
Real Time Tracking utilize wireless networks that allow you to receive data from all of the vehicles in your fleet, and view the location of any or all of your vehicles in near “real.
Real-time differential GPS
A base station which computes, formats, and transmits corrections usually through some sort of data link (e.g. VHF radio or cellular telephone) with each new GPS observation. The roving unit requires some sort of data link receiving equipment to receive the transmitted GPS corrections and get them into the GPS receiver so they can be applied to its current observations.
Real-Time Kinematic (RTK)
The DGPS procedure whereby carrier-phase corrections are transmitted in real time from a reference receiver to the user's receiver. RTK is often used for the carrier-phase integer ambiguity resolution approach
A ground station at a known location used to derive differential corrections. The reference station receiver tracks all satellites in view, computes their pseudo ranges, corrects these for errors, and then transmits the corrections to users
The accuracy with which a user can measure position relative to that of another user of the same navigation system at the same time.
The determination of relative positions between two or more receivers which are simultaneously tracking the same GPS signals.
Precision is defined as a measure of the tendency of a set of numbers to cluster about a number determined by the set (e.g. the mean). The usual measure is the standard deviation with respect to the mean. Relative precision denotes the tendency for the various components (X, Y, Z) between one station and other stations in the network to be clustered about the adjusted values.
The ability to perform a specific function without failure under specified conditions for a given length of time.
Changes in terrain; elevations or depressions in the land
A technique for showing the ups and downs of the land portrayed on a topographic map. The process makes land look three-dimensional by the use of graded shadow effects. Traditionally, maps are shaded as though the light source is coming from the northwest.
Root Mean Square. The standard deviation of the error in the GPS location.
A group of waypoints entered into the GPS receiver in the sequence you desire to navigate them.
Any mobile GPS receiver collecting data during a field session. The receiver's position can be computed relative to another, stationary GPS receiver.
The arrangement in space of a set of satellites.
Satellite Tracking System
A technology consisting of hardware and software that is installed on fleet vehicles and is used to pinpoint the location of a vehicle to within a few meters. Fleet Tracking systems usually include a wide variety of reports and alerts to notify managers of unusual or undesirable vehicle activity.
The distance between two points on a map as they relate to the distance between those same points on the earth.
Signal to Noise Ratio (SNR)The ratio of incoming signal strength to the amount of interfering noise as measured in decibels on a logarithmic scale.
A GPS observable formed by arithmetically differencing carrier phases that are simultaneously measured by a pair of receivers tracking the same satellite, or by a single receiver tracking a pair of satellites. The between-receiver's-single-difference procedure essentially removes all satellite clock errors.
Slow switching channel
A sequencing GPS receiver channel that switches too slowly to allow the continuous recovery of the data message.
The distance between the user and the reference station. When calculating differential corrections, the greater the distance between the two, the greater the error of corrections.
Speed Over Ground (SOG)
The actual speed the GPS unit is moving over the ground. This may differ from airspeed or nautical speed due to such things as head winds or sea conditions. For example, a plane that is going 120 knots into a 10-knot head wind will have a SOG of 110 knots.
The deliberate transmission of fake signals to skew the position calculations of a GPS receiver. The spoofer mimics a GPS satellite, rather like a pseudolite, but with disruptive intent.
The received GPS signal is wide bandwidth and low power. The L-band signal is modulated with a pseudo-random noise code to spread the signal energy over a much wider bandwidth than the signal information bandwidth. This provides the ability to receive all satellites unambiguously and to give some resistance to noise and multipath.
Carrier phase differencing technique where the integer ambiguities are resolved from an extended observation period through a change in satellite geometry.
Location determination when the receiver's antenna is presumed to be stationary in the earth. This allows the use of various averaging techniques that improve the accuracy by factors of over 1000.
The industry standard definition of static accuracy is the standard deviation of error if a point set by a receiver was tested in a fix position for 24 hours.
A unit of length equal to 5,280 feet or 1,760 yards (1,609 meters) used in the U.S. and some other English-speaking countries.
The act of going from one waypoint to another in the most direct line and with no turns.
Also known as 'replication,' it is the process of uploading and downloading information from two or more databases, so that each is identical.
Transmission Control Protocol/Internet Protocol. The standard set of protocols used by the Internet for transferring information between computers, handsets, and other devices.
Temporary Mobile Station Identifier. A mobile station identifier (MSID) sent over the air interface and is assigned dynamically by the network to the mobile station. See also MIN, IMSI.
Relief of the land surface; the graphic portrayal of that relief in map form by the use of contour lines.
Your current direction of travel relative to a ground position (same as Course Over Ground).
Track Up Orientation
Fixes the GPS receiver’s map display so the current track heading is at the top of the screen.
The satellite-based system that measured successive Doppler (frequency) shifts of signals transmitted from satellites in polar orbits to determine position.
A method of determining the location of an unknown point, as in GPS navigation, by using the laws of plane trigonometry.
The lowest region of the atmosphere between the surface of the earth and the tropopause, characterized by decreasing temperature with increasing altitude. GPS signals travel through the troposphere (and other atmospheric layers).
Retardation of GPS signals caused by elements in the troposphere such as temperature, air pressure, and water vapor.
The direction of the north pole from your current position. Magnetic compasses indicate north differently due to the variation between true north and magnetic north. A GPS receiver can display headings referenced to true north or magnetic north.
Ultra High Frequency (UHF)
Radio frequencies in the band from 300 to 3,000 MHz.
Universal Transverse Mercator (UTM)
A nearly worldwide coordinate projection system using north and east distance measurements from reference point(s). UTM is the primary coordinate system used on U.S. Geological Survey topographic maps.
A transmission path by which radio or other signals are sent from the ground to an aircraft or a communications satellite.
Universal Polar Stereographic, a version of UTM.
The way in which information is exchanged between the GPS receiver and the user. This takes place through the screen display and buttons on the unit.
The segment of the complete GPS system that includes the GPS receiver and operator.
The square of the standard deviation.
Images defined by sets of straight lines that are defined by the locations of the end-points. Vector graphics require much less storage space than raster or bitmapped graphics.
Vehicle Location Tracking
Technology consisting of hardware and software designed to provide detailed live and historical data on the location of fleet vehicles. Also see GPS Fleet Location, GPS Vehicle Tracking.
Velocity Made Good (VMG)
The rate of closure to a destination based upon your current speed and course.
Very High Frequency (VHF)
Radio frequencies in the band from 30 to 300 MHz.
The ability of a GPS receiver to begin navigating using almanac information stored in its memory from previous use.
Waypoints are locations or landmarks worth recording and storing in your GPS. These are locations you may later want to return to. They may be check points on a route or significant ground features. (e.g., camp, the truck, a fork in a trail, or a favorite fishing spot). Waypoints may be defined and stored in the unit manually by taking coordinates for the waypoint from a map or other reference. This can be done before ever leaving home. Or more usually, waypoints may be entered directly by taking a reading with the unit at the location itself, giving it a name, and then saving the point. Waypoints may also be put into the unit by referencing another waypoint already stored, giving the reference waypoint, and entering the distance and compass bearing to the new waypoint.
Wide Area Augmentation System (WAAS)
A system of satellites and ground stations that provide GPS signal corrections for better position accuracy. A WAAS-capable receiver can give you a position accuracy of better than three meters, 95 percent of the time. (At this time, the system is still in the development stage and is not fully operational.) WAAS consists of approximately 25 ground reference stations positioned across the United States that monitor GPS satellite data. Two master stations, located on either coast, collect data from the reference stations and create a GPS correction message.