| A | B | C | D | E | G | H | I | L | M | N | P | Q | R | S | T | U | W | Y |
| |
| A |
| 2d fix or 2D Operating Mode |
A two-dimensional GPS position fix that includes only horizontal coordinates (no GPS elevation). It requires a minimum of three visible satellites. |
| 3d fix or 3D Operating Mode |
A three-dimensional GPS position fix that includes horizontal coordinates, plus elevation. It requires a minimum of four visible satellites. |
| Accuracy |
A measure of how close an estimate of a GPS position is to the true location. |
| Acquisition Time |
The time it takes a GPS receiver to acquire satellite signals and determine the initial position. |
| Active Antenna |
An antenna that amplifies the GPS signal before sending it to the receiver. |
| Active Leg |
The segment of a route currently being travelled the "segment" being that portion of a route between any two waypoints in the route. |
| Almanac (Data) |
Information transmitted by each satellite on the orbits and state (health) of every satellite in the GPS constellation. Almanac data allows the GPS receiver to rapidly acquire satellites shortly after it is turned on. |
| Anti-Spoofing |
Encryption of the P-code to protect the P-signals from being "spoofed" through the transmission of false GPS signals by an adversary. |
| Assisted GPS (A-GPS) |
A technique for achieving certain benefits over the use of only GPS satellite signals, by using additional non-GPS data inputs, eg. WAG wireless assisted-GPS based on using the cellphone networks. Accuracy usually lower than ?true GPS' but TTFF can be faster. |
| Atomic Clock |
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. |
| 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. |
| B |
| Beacon |
Stationary transmitter that emits signals in all directions (also called a non-directional beacon). In DGPS, the beacon transmitter also broadcasts pseudorange correction data to nearby GPS receivers for greater accuracy. |
| Bearing |
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. |
| Block IIF (Program) |
The US Air Force's GPS ?Block IIF Program' involves an additional 33 satellites to provide an upgrade to current GPS (NAVSTAR) , while emphasizing compatibility and interoperability with the current GPS. Part of this programme includes adding the ?L5' frequency, intended for civilian air traffic control |
| Bullfence |
see GEOFENCE |
| C |
| Cell ID |
Every GSM mobile phone network mast sends a signal containing its Cell ID, and it is possible to read this Cell ID of the nearest-by mast on your GSM mobile phone. The Cell ID information, together with accompanying location information is used to implement location-based applications using your GSM. |
| Coarse/Acquisition Code (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. |
| Code Division Multiple Access (CDMA) |
A method for transmitting many simultaneous signals over a shared portion of the spectrum. GPS uses CDMA techniques with codes for their unique cross-correlation properties. The foremost application of CDMA is the digital cellular phone technology that operates in the 800MHz and 1.9GHz (PCS) bands. CDMA phones are noted for their excellent call quality and long battery life, and some phones can switch between both bands. CDMA is less costly to implement, requiring fewer cell sites than the GSM and TDMA digital cellphone systems and providing three to five times the calling capacity. It provides more than 10 times the capacity of the analog cellphone system (AMPS). CDMA has become widely used in North America and is also expected to become the third-generation (3G) technology used in the GSM system. |
| Clock Bias |
The difference between the indicated clock time in the GPS receiver and true universal time (or GPS satellite time). |
| Clock Offset |
A constant difference in the time reading between two clocks, normally used to indicate a difference between two time zones. |
| Cold start |
The power-on sequence where the GPS receiver downloads almanac data before establishing a position fix. |
| 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. |
| Control Segment |
A worldwide chain of monitoring and control stations that control and manage the GPS satellite constellation. |
| Course Deviation Indicator (CDI) |
A technique for displaying the amount and direction of crosstrack error (XTE). |
| 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." |
| Crosstrack Error (XTE/XTK) |
The distance you are off the desired course in either direction. |
| Cross Correlation |
Under anti-spoofing, the P code is denied to all SPS users by mixing this with a so-called W code to produce a Y code, which is transmitted from the satellite. PPS users have a key to undo all this and convert the signal back to the original P code. Most commercial and scientific geodetic GPS receivers are capable of recording a pseudorange measurement on the second frequency. One such technique for doing this is called cross correlation . Cross correlation uses the fact that the Y codes transmitted by a satellite are the same on both frequencies. Therefore by correlating the two incoming Y codes on L1 and L2, the difference between their respective times of flight can be ascertained. This difference is equal to the time delays that the frequencies suffer when they pass through the ionosphere. Adding the difference in the time delays to the L1 C/A code measurement results in a pseudorange measurement containing the same information as an actual P code measurement on L2. |
| D |
| Datum |
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. |
| Dead Reckoning |
The process of estimating your position by advancing a known position using course, speed, time and distance to be travelled. In other words figuring out where you will be at a certain time if you hold the speed, time and course you plan to travel. |
| Desired Track (DTK) |
The compass course between the "from" and "to" waypoints. |
| Differential Correction |
A technique used in DGPS. Differential corrections may be used in real-time or later, with post-processing techniques. Real-time corrections can be transmitted by radio link. The U. S. Coast Guard maintains a network of differential monitors and transmits DGPS corrections over radiobeacons covering much of the U. S. coastline. DGPS corrections are often transmitted in a standard format specified by the Radio Technical Commission Marine (RTCM). Corrections can be recorded for post processing. Many public and private agencies record DGPS corrections for distribution by electronic means. |
| Differential GPS (DGPS) |
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. |
| 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). |
| Downlink |
A transmission path for the communication of signals and data from a communications satellite or other space vehicle to the earth. |
| E |
| E911 Directive |
The United States Federal Communications Commission (FCC) directive that 95 percent of the handsets in service be able to provide location to within 50 to 100 meters by December 31, 2005. In the US, E911 leads the way for communication-linked location services and US Cell phone providers are currently phasing in this capability. This means that many handsets must be replaced, particularly those without GPS functionality. |
| Elevation |
The distance above or below mean sea level. |
| Ellipsoid |
A geometric surface, all of whose plane sections are either ellipses or circles. |
| Enhanced Cell Global Identity (E-CGI) |
The primary location accuracy is based on Enhanced Cell Global Identity (E-CGI) information. In order to get the best accuracy, advanced probability models are used to combine network measurement data with other information such as geographical maps and collected statistical data from the network. This functionality improves the location accuracy by up to 80%, enabling the implementation of services such as security applications that require a very high accuracy of positioning. |
| Enhanced Observed Time Difference (E-OTD) |
Systems operate by placing location receivers, overlaid on the cellular network as a location measurement unit (LMU) at multiple sites geographically dispersed in a wide area. Each of these LMU has an accurate timing source. When a signal from at least three base stations is received by an E-OTD software enabled mobile and the LMU, the time differences of arrival of the signal from each BTS at the handset and the LMU are calculated. The differences in time are combined to produce intersecting hyperbolic lines from which the location is estimated. E-OTD schemes offer greater positioning accuracy than cell of origin, between 50 and 125 meters, but have a slower speed of response, typically around five seconds, and require software modified handsets. |
| Ephemeris (Data) |
Current satellite position and timing information transmitted as part of the satellite data message. A set of ephemeris data is valid for several hours. |
| 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. |
| G |
| GALILEO |
European programme to develop an independent satellite-based positioning system, taking advantage of technological innovation whilst optimising the compatibility and interoperability with GPS/NAVSTAR. |
| Gazetteer |
A database of place and geographic location information, usually providing location co-ordinates, etc., as used in GPS-based equipment. |
| Geocaching |
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. |
| Geodetic Datum |
A mathematic model representing the size and shape of the earth (or a portion of it). |
| Geofence |
A (typically) user-defined fixed enclosed area on a map (ie. a boundary ) eg. used to initiate an action/signal if the ?geofence' is crossed by the target (often referred to in AVL and asset-tracking applications.) |
| 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. |
| Geostationary or Geosynchronous Earth Orbit(GEO) |
A specific orbit 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 and is 22,282 miles above the equator. GEOs are excellent for TV broadcasting, but produce distracting, half-second delays in interactive voice conversations, because of the long round trip from earth and back. LEOs and MEOs , which are closer to the earth, are being deployed for interactive services. |
| Global Positioning System (GPS) |
A global navigation system based on 24 or more satellites orbiting the earth at an altitude of 12,000 statue miles and providing very precise, worldwide positioning and navigation information 24 hours a day, in any weather. Also called the NAVSTAR system. |
| GLONASS |
The Global Orbiting Navigational Satellite System - the Russian counterpart to the United States' GPS system. |
| Global System for Mobile Communications (GSM) |
A digital cellular phone technology based on TDMA that is widely deployed in Europe and throughout the world. GSM coverage is increasing in the U.S. Most PCS phones use GSM and operate in the 1.8 to 1.9GHz band, compared to 800-900MHz for other cellular systems. Higher frequencies extend battery life. See also TDMA, CDMA, and PCS. |
| GoTo |
A route consisting of one leg, with your present position being the start of the route and a single defined waypoint as the destination. |
| GPS sentence protocols |
see NMEA Sentences |
| H |
| Heading |
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. |
| Healthy |
A term used when an orbiting GPS satellite is suitable for use. "State" is also used to refer to satellite health. |
| Height and speed restrictions |
The speed and altitude restrictions are imposed by the International Traffic in ARMS Regulations (ITAR) for the export of GPS receivers. These are 1000 knots and 60000 feet, respectively. For more information, see the article in GPS World, October 2000, "This is Rocket Science: Multiple Payload Tracking in Space", by Barton Bull (pp 22 to 32). |
| I |
| IEC 529 |
A European system of test specification standards for classifying the degrees of protection provided by the enclosures of electrical equipment. An IPX7 designation means the GPS case can withstand accidental immersion in one meter of water for up to 30 minutes. An IPX8 designation is for continuous underwater use. |
| Initialization |
The first time a GPS receiver orients itself to its current location and collects almanac data. After initialization has occurred, the receiver remembers its location and acquires a position more quickly because it knows which satellites to look for. |
| Ionosphere / Ionospheric variation |
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. |
| Invert Route |
Displaying and navigating a route in reverse, ie. from end to beginning for purposes of returning to the route's starting point. |
| IPX7 |
see IEC529 |
| L |
| L Band |
The radio frequencies that extend from 390 MHz to 1550 MHz. The GPS carrier frequencies (1227.6 MHz and 1575.42 MHz) are in the L band. |
| Latitude |
The distance north or south of the equator, measured in degrees (0 to 90) and minutes. One minute of latitude equals one nautical mile. |
| L-commerce |
location-based services eg. using GPS to determine position/location |
| Line Of Sight (LOS) Propagation |
(of an electromagnetic wave) 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 Area Augmentation System (LAAS) |
The ground-based DGPS to support aircraft landings in a local area (20-mile range). |
| Longitude |
The distance east or west of the prime meridian (measured in degrees and minutes). The prime meridian runs from the north to south pole through Greenwich, England. |
| LORAN |
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. |
| Low Earth Orbiting (LEO) |
LEO satellites orbit the earth at between 300km and 1500 km in polar and inclined orbits. Used for the purposes of scientific research, remote sensing, surveilance, meteorology, satellite imaging and other applications. LEO and MEO (Medium Earth Orbiting) satellite sytems using these orbits are also being implemented for mobile and personal communications and increasingly more for interactive services (See also GEO and MEO) |
| M |
| Magnetic North |
Represents the direction of the north magnetic pole from the observer's position. This is displayed on a compass. |
| Magnetic Variation |
The horizontal angle (or difference) between true north and magnetic north - measured ?east or west of true north'. |
| m-commerce |
Mobile based commerce, eg. shopping by credit card using an online service over the cellphone network. |
| 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 reference in determining both land elevation & sea depths. |
| Medium Earth Orbit (MEO) |
Satellites on MEO orbits have greater heights than LEO orbits, usually between 5,000 and 15,000 km. (See also LEO & GEO) |
| MS assisted |
Refers to A-GPS (eg. WAG) solutions where the mobile equipment sends data to the WAG Server (part of the mobile network infrastructure) for position calculation (see also MS-based) |
| MS based |
As per ?MS assisted' but where extra functionality is integrated into the mobile (eg. handset) to calculate position. |
| MTSAT Satellite based Augmentation System (MSAS) |
An overlay system for the GPS service which enhances the accuracy of GPS navigation by transmitting differential information. MSAS can be used for Japan & Australia) (See also WAAS, EGNOS) |
| MTSAT |
A dual mission satellite for the Japanese Ministry of Transport and the Japan Meteorological Agency performing an air traffic control and navigation function as well as a meteorological function. |
| Multipath Error |
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. |
| Multiplexing Receiver |
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. |
| N |
| Nautical Mile |
A unit of length used in sea and air navigation, based on the length of one minute of arc of a great circle and is equal to 1,852 meters (about 6,076 feet). |
| Navigation Message |
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'. |
| NMEA sentences / messages (standards) |
A NMEA standard defines an electrical interface and data protocol for communications between marine instrumentation, eg. ?GPS sentence protocols' |
| North Up Orientation |
A GPS receiver's map display mode whereby north is always fixed at the top of the screen. |
| P |
| Parallel Channel Receiver |
A continuous tracking receiver using multiple receiver circuits to track more than one satellite simultaneously. |
| P codes |
The precise code of the GPS signal typically used only by the U.S. military. It is encrypted and reset every seven days to prevent use from unauthorized persons. (See also Y-Code) |
| Permission-based marketing |
The backlash against what is formally called unsolicited commercial e-mail what most of us refer to as spam, when some stronger description doesn't come to mind has forced online marketers to find more responsible ways to communicate with their potential customers. Methods regarded as acceptable in direct mail, such as buying lists of prospects from a list broker, are considered objectionable online. And the electronic medium makes it difficult for list brokers to retain control over a list of addresses. One solution being tried is an opt-in system in which people sign up to receive messages about specific kinds of products from a middleman. This firm doesn't sell lists of addresses, but instead forwards information supplied by marketers to people on its list who say they want to receive it. This system has been given the name of permission-based marketing, a term that is still mainly jargon, but which is beginning to appear more widely. Other forms of the phrase which have also been used are permission e-mail marketing and permission-based direct marketing. |
| Personal Communications Services (PCS) |
Refers to a variety of wireless services emerging after the U.S. Government auctioned commercial licenses in late 1994 and early 1995. This radio spectrum in the 2GHz range is used for digital transmission services that compete with analog cellular (AMPS), digital cellular and other wireless services. |
| Position Fix |
The GPS receiver's computed position coordinates. |
| Position Format |
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) |
Authorized users with cryptographic equipment and keys and specially equipped receivers use the PPS. US and Allied military, certain U. S. Government agencies, and selected civil users specifically approved by the US Government, can use the PPS. PPS Predictable Accuracy :
- 22 meter Horizontal accuracy
- 27.7 meter vertical accuracy
- 200 nanosecond time (UTC) accuracy
|
| Prime Meridian |
The zero meridian, used as a reference line from which longitude east and west is measured. It passes through Greenwich, England. |
| PRN code |
Pseudo Random Noise Code - see Pseudo-Random Code |
| Pseudo-Random Code |
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 Range |
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. |
| Q |
| Quadrifilar Helix Antenna |
A type of GPS antenna in which four spiraling elements form the receiving surface of the antenna. For GPS use, quadrifilar antennas are typically half-wavelength or quarter-wavelength size and encased in a plastic cylinder for durability. |
| R |
| Receiver Autonomous Integrity Monitoring (RAIM) |
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. |
| Ring Ping |
A technique employed in mobile phone based systems whereby a call received from a recognised caller (based on its CLI) initiates an action without answering the call, hence ..at no call cost. |
| S |
| Selective Access or Selective Availability (SA) |
The random error, which the government can intentionally add to GPS signals, so that their accuracy for civilian use is degraded. SA is not currently in use. |
| Sidereal day |
The time required for a complete rotation of the earth in reference to any star or to the vernal equinox at the meridian, equal to 23 hours, 56 minutes, 4.09 seconds in units of mean solar time. |
| Space Segment |
The satellite portion of the complete GPS system. |
| 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. |
| Spread Spectrum |
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. |
| Standard Positioning Service |
The civil and commercial service provided by the basic GPS. SPS provides a Predictable Accuracy of :
- 100 metres horizontal accuracy
- 156 metres vertical accuracy
- 340 nanoseconds time accuracy
|
| T |
| THATCHAM |
An approval standard for automotive security. |
| Time Division Multiple Access (TDMA) |
A satellite and cellular phone technology that interleaves multipledigital signals onto a single high-speed channel. For cellular, TDMA triples the capacity of the original analog method (FDMA). It divides each channel into three subchannels providing service to three users instead of one. See also CDMA. |
| Time To First Fix (TTFF) |
If you have not used your GPS unit for several months, the almanac data for the satellites may be out of date. The unit is capable of recollecting this information on its own, but the process can take several minutes. Time to First Fix (TTFF) is the time it takes a GPS receiver to find satellites after the user first turns it on (when the GPS receiver has lost memory or has been moved over 300 miles from its last location). |
| Triangulation |
A method of determining the location of an unknown point, as in GPS navigation, by using the laws of plane trigonometry. |
| Troposphere |
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). |
| True North |
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. |
| U |
| User Segment |
The segment of the complete GPS system that includes the GPS receiver and operator. |
| UTC time |
see Coordinated Universal Time. |
| W |
| Waypoints |
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 favourite 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. |
| Whereware |
The hardware and software that make locating a person possible an MIT expression. |
| World Geodetic Reference 84 (WGS-84) |
World Geodetic System, 1984. The primary map datum used by GPS - a complete approximate model of the earth. Secondary datums are computed as differences from the WGS 84 standard. |
| Y |
| Y-Code |
the encrypted P-Code (See P-Code) |
