Glossary

Accuracy
A measure of how close a GPS position is to the true location. 
 
Active Leg
In GPS this is the segment (section between two waypoints) of a route currently being travelled.  

Active Matrix Display
An LCD technology used in flat panel computer displays; it produces a brighter and sharper display with a broader viewing angle than passive matrix screens. Active matrix technology uses a thin film transistor at each pixel and is often designated as a TFT screen. 
 
ActiveSync
Software which allows you to synchronise the information on your computer with the information on your compatible handheld. Synchronisation compares the data on your handheld with your computer and updates both computers with the most recent information. Synchronisation is done via an USB cable, a USB cradle, Bluetooth, or other wireless connection

Advanced Research and Global Observation Satellite
An advanced research and development satellite launched by the United States Air Force. Carries various space and atmospheric experiments. 
 
Agonic line
An imaginary line on the earth's surface connecting points where the magnetic declination is zero. 
 
Alarm/Charge Light
Serves as both a battery charge indicator and a visual alarm indicator. 
 
Almanac
A data file that contains the approximate orbit information of all satellites. This set of parameters is transmitted regularly by all GPS satellites, and allows for a receiver to predict the approximate location of a satellite rapidly. Most receivers provide a facility for battery backup or non-volatile storage of the almanac to make power-on acquisition faster. The almanac is less accurate then ephemeris data, but remains valid for a longer period. 
 
Altimeter
An instrument that measures altitude or elevation with respect to a reference level, usually mean sea level, by means of air pressure. 
 
Ambient Light Sensor
A light sensor at the top of the screen which gauges ambient light in the environment and automatically adjusts the brightness of the screen for optimum viewing. This takes away the frequent and tedious task of manually adjusting brightness on the screen; it is particularly beneficial in environments where light is subject to change throughout the day. 
 
Analogue Signal
The principal feature of analogue signals is that they are continuous. In contrast, digital signals consist of values measured at discrete intervals. 
 
Antenna
That part of the GPS receiver hardware which receives (and sometimes amplifies) the incoming signal. 
 
Anywhere Fix
The ability of a receiver to start position calculations without being given an approximate location and time. 
 
Application
A program, such as a word processor or a spreadsheet, that performs one of the important tasks for which a desktop or handheld computer is used. This term is sometimes use in place of or in conjunction with software. 
 
Application Buttons
Buttons on your Handheld that allows quick access to applications you use frequently, such as Contacts and Calendar.

ARGOS
See Advanced Research and Global Observation Satellite 
 
Ascending Node
The point at which an orbiting object passes the reference plane from south to north. 
 
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. 
 
Attenuation
A reduction in signal strength 
 
Automatic Vehicle Location (AVL)
A system of providing real-time location information for emergency vehicles, delivery trucks, service vehicles, etc. The technique of using a navigation system, such as GPS, to determine a vehicle's position. 
 
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. 
 
Availability
The number of hours per day that a particular location has sufficient satellites to make a GPS position determination possible. 
 
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. 
 
AVM
See Automatic Vehicle Monitoring 
 
AVL
See Automatic Vehicle Location 

Backup
A copy of a file, directory, or volume on a separate storage device from the original, for the purpose of retrieval in case the original is accidentally erased, damaged, or destroyed.

Backlight
An LCD screen that has its own light source from the back of the screen, making the background brighter and characters appear sharper.

Bandwidth
That range of frequencies that compose a signal. Expressed in Hertz.

Base Station
Also called a Reference Station. A ground station at a known location used to derive differential corrections to GPS signals. The reference station receiver tracks all satellites in view, computes their pseudoranges, corrects these for errors, and then transmits the corrections to users. In the case of Differential GPS (DGPS) the base station calculates the error for each satellite and, through differential correction, improves the accuracy of GPS positions.

Battery
A battery is an electrochemical cell or enclosed and protected material that can be charged electrically and provide a static potential for power or released electrical charge when needed.

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.

Beaming
Term coined by Palm to describe the way to transmit data from one PDA to another via infrared ports.

Bearing
See azimuth. In a GPS receiver, bearing usually refers to the direction to a waypoint.

Bench mark
A material object, natural or man-made, with a known elevation or horizontal location. Bench marks can be used as reference points when travelling a route or in determining the elevation of nearby land features.

Bias
All GPS measurements are affected by biases and errors, such as atmospheric conditions. Their combined magnitudes will affect the accuracy of the positioning results (they will bias the position or baseline solution). Biases may be defined as being errors that cause the true measurements to be different from observed measurements by a constant, predictable or systematic amount.

Bit
A unit of information in an electronic system expressed as a choice between two possible values, for example, 0 or 1.

Bitmap image
An image with 1 bit of colour information per pixel, also known as a bitmapped image.

Bluetooth
A short range, wireless networking technology allowing personal devices such as a PDA, GPS unit, computer, printer or mobile phone to exchange and synchronise data. It works on short range as long as the devices are up to approximately 10metres apart.

Brightness
A measure of the overall intensity of the image. The lower the brightness value, the darker the image; the higher the value, the lighter the image will be.

Bluetooth GPS (BTGPS)
When a device, such as a PDA is linked to a GPS receiver via Bluetooth.

C/A Code
See Coarse/Acquisition Code

Cache Memory
Cache memory is random access memory (RAM) that a computer microprocessor can access more quickly than it can access regular RAM.

Carrier
A steadily transmitted RF signal (radio wave) whose amplitude, frequency or phase (or a combination) may be modulated from a known reference to carry information.

Carrier-Aided Tracking
A method to improve accuracy by using the GPS carrier signal to get a more precise lock on the pseudorandom (PRN) code.

Carrier Frequency
The frequency of an unmodulated output of a radio transmitter. The GPS L1 carrier frequency is 1575.42 MHz.

Carrier-Tracking Loop
A module in a GPS receiver that demodulates, or extracts, the satellite message by aligning the phase of the receiver's local Oscillator">oscillator signal with the phase of the frequency-shifted, received carrier.
Once the local Oscillator">oscillator signal is locked to the carrier, its phase can be measured to provide the carrier-phase observation.

Cartography
The art or technique of making maps or charts. Many GPS receivers have detailed mapping – or cartography – capabilities.

CCD
A digital camera is very much like a camcorder. Rather than focusing the image of the scene you wish to record on film, a digital camera focuses the image onto a light-sensitive chip (CCD) which in TRN)+">turn converts the image into digital form.

CDI
See Course Deviation Indicator

CDMA
See Code Division Multiple Access

CEP
See Circular Error Probable

CF card
See Compact Flash card

Channel
A channel of a GPS receiver consists of the circuitry necessary to receive the signal from a single GPS satellite.

Chip
Binary elements or digits that, unlike bits, convey no information. A PRN code consists of a sequence of chips.

Chip Rate
The number of chips sent per second.

Chartplotter
A device that overlays GPS data on to marine navigational charts.

Circular Error Probable (CEP)
The radius of a circle within which fifty percent of positioning solutions fall. CEP is used to achieve horizontal accuracy.

Clinometer
A device, usually similar to a compass, used to measure vertical angles, as in the slope of a hill.

Clock Aiding
An accuracy enhancement technique in which an additional atomic clock (rubidium) provides accurate time to the receiver for calculating satellite clock frequency, phase bias, and clock bias.

Clock Bias
The difference between the indicated clock time in the GPS receiver and true universal time (or GPS satellite time).

CMG
See Course Made Good

Coarse/Acquisition Code (C/A Code)
Also known as the Civilian Code or S-Code. The standard positioning signal the GPS satellite transmits to the civilian user. A sequence of 1023 pseudo-random, binary, biphase modulations on the GPS carrier at a chip rate of 1.023 MHz. It contains the information the GPS receiver uses to fix its position and time, and is accurate to 100 metres or better.

Code Division Multiple Access (CDMA)
A method of frequency sharing where many transmitters use the same frequency but each one has a unique code to generate pseudorandom sequences. GPS uses CDMA with Gold codes.

Code-Tracking Loop
A module in a GPS receiver used to align a PRN code sequence present in a signal coming from a satellite with an identical PRN code sequence generated within the receiver. Alignment is achieved by appropriately shifting the receiver-generated code chips in time so that a particular chip in the sequence is generated at the same instant its twin arrives.

COG
See Course Over Ground

Cold Start
Used to describe state where a GPS receiver is powered on and does not have valid almanac data available. This lengthens the time required to locate satellites and arrive at the first position solution.

COM Ports
The connectors and accompanying circuitry that allow serial devices (usually serial printers, modems, or mice) to be connected to PC. Communication ports are also called serial ports. To keep track of the devices, DOS assigns names that begin with the letters COM to communication ports (such as COM1 and COM2).

Commercial Software
Software that must be purchased before use. There is no “testing” period available before the customer must spend money for the product.

Communications Port
Connects your PDA to its cradle (or to an optional USB or serial cable)

Compact Flash card (CF card)
Cards that can be used in small devices like handhelds. They can be used for storage (memory) or to accept removable accessories such as additional memory or GPS receivers.

Constellation
Refers to either the specific set of satellites used in calculating a position, or all the satellites visible to a GPS receiver at one time, or the entire ensemble of GPS satellites comprising the Space Segment.

Control Point
Also called a control station. Locations on the earth's surface used for mapping references. Can be horizontal or vertical or both. Often these are bench marks.

Control Segment
A worldwide chain of monitoring and control points that control and manage the GPS satellite constellation.

Control Station
See Control Point

Contour interval
The difference, in feet or meters, in elevation between two adjacent contour lines.

Contour line
A line on a topographic map that represents a specific elevation.

Coordinates
A set of numbers that represents a precise location anywhere on Earth. Usually stated as latitude and longitude.

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.

Course
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 leg.

Course Deviation Indicator (CDI)
A technique for displaying the amount and direction of crosstrack error (XTE).

Course Made Good (CMG)
The bearing from your starting point to your present position. Commonly used in marine or air navigation.

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”

Cradle (USB/Serial)
This holds your PDA and acts as a communication conduit between the PDA and the computer. You can synchronize data and download programs from the PC. Some cradles double as battery chargers. USB and Serial are the types of ports on the computer to which you attach the cradle.

Crosstrack Error (XTE/XTK)
The distance you are off a desired course in either direction.

Cut-off Angle
The minimum acceptable satellite elevation angle (above the horizon) to avoid blockage of line-of-sight, multipath errors or high Tropospheric or Ionospheric Delay values. May be preset in the receiver, or applied during data post-processing. For navigation receivers may be set as low as 5°, while for GPS Surveying typically a cut-off angle of 15° is used.

Cycle Slip
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.

Data Message
See Navigation Message

DC Jack
Allows you to connect to external power with the supplied AC adapter.

Dead Reckoning (DR)
The technique of determining position by computing distance travelled on a given course. Distance travelled is determined by multiplying speed by elapsed time.

Delay-Lock Loop
Another term for a code-tracking loop

Demodulation
Separating coded data from the carrier signal.

Depression contour
A contour line with hachures (small perpendicular tick marks) to signify a depression

Desired Track (DTK)
The compass course between two waypoints.

Device Driver
A software routine that links a peripheral device to the operating system. It acts like a translator between a device and the applications that use it. Each device has its own set of specialised commands known only to its driver. In contrast, most applications access devices by using high-level, generic commands. The driver accepts these generic and translates them into the low-level specialised commands required by the device.

DragonBall processor
Computer processor manufactured by Motorola on which Palm OS® devices run

Degree
A unit of measurement; 360 degrees equal one complete circle, as around the earth on a line of latitude; measured from 0 to 90 degrees from the equator to each pole along a line of longitude.

DGPS
See Differential GPS

Differential GPS (DGPS)
A method of improving GPS accuracy using measurements at known locations to improve the measurements made by other GPS receivers within the same general area. DGPS reduces the effect of selective availability, propagation delay, etc. and can improve position accuracy to better than 10 metres.

Differential Positioning
Also known as Relative Positioning. Precise measurement of the relative positions of two receivers tracking the same GPS signals. May be considered synonymous with DGPS, or the term may be reserved for the more precise carrier phase-based baseline determination technique associated with GPS Surveying.

Dilution of Precision (DOP)
A value expressing the confidence factor in the accuracy of the position solution based on current satellite geometry. The lower the value the greater the confidence in the solution. DOP can be expressed in the following forms: GDOP - All parameters are uncertain (latitude, longitude, height, clock offset). HDOP - 2D parameters are uncertain (latitude, longitude). HTDOP - 2D parameters and time are uncertain (latitude, longitude, time). PDOP - 3D parameters are uncertain (latitude, longitude, height). TDOP - Clock offset is uncertain. VDOP - Height is uncertain.

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.

Distance
The length (in feet, metres, miles, etc.) between two waypoints or from your current position to a destination waypoint. This length can be measured in straight-line (rhomb line) or great-circle (over the earth) terms. GPS normally uses great circle calculations for distance and desired track.

Dithering
The introduction of digital noise. This is the process the DOD uses to add inaccuracy to GPS signals to induce Selective Availability, that is to degrade GPS position accuracy for civilian users.

DOD
The United States Department of Defence. The DOD manages and controls the Global Positioning System.

Doppler Shift
aka the Doppler Effect. In GPS. The apparent change in the frequency of a signal caused by the relative motion of the transmitter and receiver.

Doppler Aiding
A signal processing strategy that uses a measured Doppler Shift to help the receiver smoothly track the GPS signal. This allows for more precise velocity and position determination, especially when the receiver is moving at high speed and/or in an erratic fashion.

Downlink
A transmission path for the communication of signals and data from a communications satellite or other space vehicle to the earth.

DR
See Dead Reckoning

DRMS
See Distance Root Mean Square

DTK
See Desired Track

ECDIS
See Electronic Charting Display Information System

EGNOS
See European Geostationary Navigation Overlay Service

Electronic Charting Display Information System
A system with sufficient precision that commercial navigation can be accomplished without the aid of paper charts.

Elevation
Height above mean sea level.

Elevation Mask Angle
The elevation angle below which satellites are ignored in the position calculation. Typically set to around 5-10 degrees to avoid interference problems from obstructions and atmospheric errors.

EPE
See Estimated Position Error

Ephemeris
(Plural Ephemerides)A description of the path of a celestial body (e.g. a satellite) indexed by time (from the Latin word, ephemeris, meaning diary). The navigation message from each GPS satellite includes a predicted ephemeris for the orbit of that satellite. The ephemeris is repeated every 30 seconds and is valid for the current hour

EPOC
The operating system of the Symbian platform, which works best with low-power, compact machines and long-running applications. It was developed and licensed by Symbian. See Symbian.

Epoch
Measurement interval or frequency at which data is measured. For example a GPS receiver reporting a position once every two seconds as an epoch of two seconds. Also a particular instant of time or a date for which values of data are given, or a given period of time during which a series of events take place.

Equator
An imaginary line around the Earth at 0 degrees latitude

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 i.e. The distance the GPS receiver may be off target.

Estimated Time Of Arrival (ETA)
The estimated time you will arrive at a destination.

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.

European Geostationary Navigation Overlay Service (EGNOS)
A European system of satellite navigation. It will augment the two satellite navigation systems now operating, the U.S. GPS and GNSS systems. It consists of three geostationary satellites and a network of ground stations. EGNOS will achieve its aim by transmitting a signal containing information on the reliability and accuracy of the positioning signals sent out by GPS and GNSS.

E-text
Text in an electronic text format that can be read by devices such as Palm OS® devices.

ETA
See Estimated Time Of Arrival

ETE
See Estimated Time Enroute

Expansion Card
A printed circuit card such as a video card that plugs into an expansion slot and adds functionality to the PC.

Expansion Slot
Compartments in a PC or handheld into which you can plug expansion cards and connect them to the system bus. Depending on the manufacturer, these cards may be used for add-ons, including memory, MP3 players, modems, pagers, games, digital cameras, and global positioning systems.

Fast switching channel
In GPS. A single channel which rapidly samples a number of satellite ranges.

FDGC
See Federal Geographic Data Committee

Federal Geographic Data Committee (FDGC)
An agency established by the United States Federal Office of Management and Budget responsible for the coordination of development, use, sharing, and dissemination of surveying, mapping, and related spatial data.

Federal Radionavigation Plan (FRP)
An official U.S. government document, published biennially, that outlines radionavigation planning and policy.

Fix
Defining position, where two lines such as latitude and longitude cross, as determined by one or more navigation aids or techniques.

Fixed Dialling
With fixed dialling the mobile user can define a number of specific dial numbers for his line to be able to call. All attempts to call numbers other than the defined ones will be rejected. The main function of this is to improve security/control.

Flash Memory
Flash memory is a non-volatile memory device that retains its data when the power is removed.

Fluxgate compass
An electronic device used to measure magnetic direction.

Form factor
A term used to describe the way a device is constructed, such as its shape. For example, GPS receivers come in many form factors, such as handheld, PDA, automotive, USB, etc.

FPS
Frames Per Second. Mostly used in conjunction with video.

Freeware
Software offered free of charge by the developer to anyone wishing to use it

Frequency
The number of waves passing a specific point within a unit period of time, expressed in Hertz (cycles per second).

Frequency band
A particular range of frequencies

Frequency Modulation
A method of encoding information about a carrier signal by altering the frequency while amplitude remains constant.

Frequency spectrum
The distribution of signal amplitudes as a function of frequency.

FRP
See Federal Radionavigation Plan

Fundamental Frequency
The fundamental frequency of GPS is 10.23MHz. The carrier L1 is 154F = 1575.42MHz and the L2 carrier is 120F = 1227.60MHz.

Galileo
Europe's satellite navigation system.

GANS
See Global Access, Navigation, and Safety

GDOP
See Geometric Dilution of Precision

General Packet Radio Service (GPRS)
Technology that enables high-speed wireless internet and other data communications for uses such as mobile phones and computers. GPRS requires a GSM network and subscription. If you want to quickly send and receive email or surf the web from your PDA, you should consider using a device and service that supports GPRS. GPRS supports data transfer speeds of 56 to 114 Kbps. With General Packet Radio Service (GPRS) you can enjoy a continuous wireless connection to data networks and access your favourite information and entertainment services. GPRS technology allows mobile phones to be used for sending and receiving data over an Internet Protocol (IP)-based network. GPRS as such is a data bearer that enables wireless access to data networks like the Internet. The applications using GPRS are WAP, MMS, SMS, Java and the PC dial-up (for example, Internet and e-mail). GPRS allows the user faster call set-up, higher data speed, and an “always on” connection.

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.

Geofence
An imaginary boundary set which contains a GPS device - if that GPS device exceeds the boundary, an alarm is activated.

Geographic Information System (GIS)
A system of hardware and software used for storage, retrieval, mapping, and analysis of geographic data.

Geographic Names Information System (GNIS)
Developed by the USGS in cooperation with the U.S. Board on Geographic Names (BGN). It contains information about almost 2 million physical and cultural geographic features in the United States.

Geomatics
The science and technology of gathering, analyzing, interpreting, distributing, and using geographic information.

Geometric Dilution of Precision (GDOP)
Since a GPS receiver determines position by triangulation, when the GPS satellites that are being received are clustered too close together, the positional accuracy determined by the receiver is diluted. The wider the angle between satellites, the better the measurement. See Dilution of Precision.

Geosynchronous Orbit
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. GPS satellites are not geostationary. aka Geostatic, Geostationary

GIS
See Geographic Information System

Global Access, Navigation, and Safety (GANS)
A United States Air Force program that is a potential vehicle for collaboration. GANS is an umbrella avionics program that integrates GPS, navigation and safety equipment, Navigation Warfare (NAVWAR), avionics modernization, military ground-based infrastructure, Global Air Traffic Management (GATM), and the Joint Precision Approach and Landing System (JPALS).

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. Also called the NAVSTAR system. For more information, see About GPS.

Globalstar
A handheld satellite phone service.

Global System for Mobile communications (GSM)
One of the leading digital cellular systems. GSM allows eight simultaneous calls on the same radio frequency. First introduced in 1991, by the end of 1997, GSM service was available in more than 100 countries and has become the de facto standard in Europe and Asia. GSM Services include: GPRS and SMS. Similar to PCS but not compatible.

GLONASS
aka GNSS - Global Navigation Satellite System
The Global Orbiting Navigational Satellite System; the Russian counterpart to the United States’ GPS system. It consists of a constellation of 24 satellites (though the number may vary due to difficulties in funding for the system) transmitting on a variety of frequencies in the ranges from 1597-1617MHz and 1240-1260MHz (each satellite transmits on two different L1 and L2 frequencies).GLONASS provides worldwide coverage, however, its accuracy performance is optimised for northern latitudes, where it is better than GPS's SPS (there being no "Selective Availability" on GLONASS satellites). GLONASS positions are referred to a different Datum to those of GPS, i.e. PZ90 rather than WGS84. Some GPS receivers use a combination of both NAVSTAR and GLONASS to provide enhanced capabilities.

GMT
See Greenwich Mean Time

GNIS
See Geographic Names Information System

GoTo
A function on most GPS receivers that, when enabled, guides the user from their current location to one specific destination.

GPRS
See General Packet Radio Service

GPS ICD-200
Specification that contains full technical details on how a GPS receiver must interface with the system.

GPS Receiver
Electronic equipment that passively receives GPS signal for processing. A receiver may be hand-held or permanently mounted on a vehicle.

GPS (System) Time
The time scale to which GPS signals are referenced. GPS Time derives from a composite 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. At the integer second level, GPS Time equalled UTC in 1980, but currently, due to the leap seconds that have been inserted into UTC, it is ahead of UTC by more than 10 seconds. The relationship between GPST and UTC is transmitted within the Navigation Message.

GPS Week
The number of elapsed weeks since the week beginning 6th January 1980. The week number sequentially increments at Saturday/Sunday midnight in GPS (system) Time.

Graffiti
Graffiti is a character recognition software that enables users to quickly input data into touchscreen units. Graffiti is closely related to the ASCII character set which allows users to learn the input system relatively easily.

Graticule
Network of parallels and meridians on a map or chart.

Great circle
A circle described by the intersection of the surface of the Earth with a plane passing through the centre of the Earth. The shortest distance between two points on the surface of the Earth is a segment of a great circle. 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.

Grid
A pattern of regularly spaced horizontal and vertical lines forming square zones on a map used as a reference for establishing points. Common map grids include that defined by the UTM (Universal Transverse Mercator) projection.

Ground Speed
The velocity you are travelling relative to a ground position. Typically measured in "knots" (nautical miles per hour), but may be expressed in km/hr or m/s.

Ground Wave
A radio wave that travels along the earth’s surface.

Hachure
Short lines attached to, and perpendicular with a contour line usually used to indicate a depression contour.

Handheld Device/Computer
A handheld computer is a computer that can conveniently be stored in a pocket (of sufficient size) and used while you're holding it. Today's handheld computers, which are also called personal digital assistants (PDAs), can be divided into those that accept handwriting as input and those with small keyboards.

Hand-Over Word (HOW)
The word in the GPS message that contains synchronization information for the transfer of tracking from the C/A to P code.

HDOP
See Horizontal Dilution of Precision

Heading
The direction in which a you are moving.

Healthy
A term used when an orbiting GPS satellite is suitable for use. “State” is also used to refer to satellite health.

Height Aiding
An accuracy enhancement technique in which the known height of the receiver is entered into the navigation solution, which in effect provides another Satellite’s range.

Hertz (Hz)
A unit used to measure a wave’s frequency, one cycle per second.

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. See also Dilution of Precision

Horizontal Time Dependent Positioning (HTDP)
A computer database and interpolation program to predict horizontal displacements between coordinate points over time. See also Dilution of Precision

Hotsync
HotSync(TM) is the technology utilized by the Palm Computing Platform that enables the data transfer between the Palm units and the PC or Mac. The HotSync application provides data synchronization for the built-in applications and the automatic backup of 3rd-party application databases. Therefore, as long as your applications are correctly configured to backup the data during HotSync, you will always have a fairly current backup of your Palm data on your PC or Mac. OS (Operating System)

HOW
See Hand-Over Word

HTDP
See Horizontal Time Dependent Positioning

Hz
See Hertz

Hachure
Short lines attached to, and perpendicular with a contour line usually used to indicate a depression contour.

Handheld Device/Computer
A handheld computer is a computer that can conveniently be stored in a pocket (of sufficient size) and used while you're holding it. Today's handheld computers, which are also called personal digital assistants (PDAs), can be divided into those that accept handwriting as input and those with small keyboards.

Hand-Over Word (HOW)
The word in the GPS message that contains synchronization information for the transfer of tracking from the C/A to P code.

HDOP
See Horizontal Dilution of Precision

Heading
The direction in which a you are moving.

Healthy
A term used when an orbiting GPS satellite is suitable for use. “State” is also used to refer to satellite health.

Height Aiding
An accuracy enhancement technique in which the known height of the receiver is entered into the navigation solution, which in effect provides another Satellite’s range.

Hertz (Hz)
A unit used to measure a wave’s frequency, one cycle per second.

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. See also Dilution of Precision

Horizontal Time Dependent Positioning (HTDP)
A computer database and interpolation program to predict horizontal displacements between coordinate points over time. See also Dilution of Precision

Hotsync
HotSync(TM) is the technology utilized by the Palm Computing Platform that enables the data transfer between the Palm units and the PC or Mac. The HotSync application provides data synchronization for the built-in applications and the automatic backup of 3rd-party application databases. Therefore, as long as your applications are correctly configured to backup the data during HotSync, you will always have a fairly current backup of your Palm data on your PC or Mac. OS (Operating System)

HOW
See Hand-Over Word

HTDP
See Horizontal Time Dependent Positioning

Hz
See Hertz

Illumination
The signals coming from GPS satellites.

Inclination
One of the orbital parameters that describes the orientation of an orbit. It is the angle between the orbital plane and a reference plane.

Index contour
A contour line on a topographic map that is labelled as to elevation; used as a reference.

Infrared (IrDA)
Infrared data association. IrDA's goal is to establish standards for the exchange of data over infrared waves. Infrared technology would let devices "beam" information to each other in the same way that your remote control tells the TV to change the channel. You could, for example, beam a document to your printer instead of having to connect a cable. On handhelds, the most common use for infrared is the "beaming" of data to another handheld with an infrared port. The IrDA standard has been widely adopted by PC and consumer electronics manufacturers.

Infrared port
An infrared port that facilitates the short range beaming of information between PDAs and other electronic devices such as printers, computers and televisions.

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. Also, 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.

Input/Output (I/O)
Refers to data transfer from input devices (keyboard, mouse, scanner, etc.) to output devices (printer, screen, etc.).
Also, the two-way transfer of GPS information with another device, such as a navigation plotter, autopilot, or another GPS unit.

I/O Address
Memory location for a particular device (disk drive, sound card, printer port, etc.). Two devices cannot share the same I/O address space.

Integrity
A quality measure of GPS performance for critical applications such as civilian aviation. 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. A high level of integrity is sought for such applications.

Interference
Any distortion of the transmitted signal that impedes the reception of the signal at the receiver (same as noise).

Interferometric Differencing
A variation of phase differencing in which two different antennas sample the GPS signal wavefront at two locations and then feed the information into a single amplifier and mixer (interferometer) in which phase difference observations are made.

Internet
The global computer network, composed of thousands of WANs and LANs that uses TCP/IP to provide world-wide communications to homes, schools, businesses and governments. The WWW runs on the Internet.

Intranet
Computers linked through a network, usually within a single company's premises.

Ionosphere
That layer of the atmosphere approximately 30-300 miles above the earth’s surface that contains electrically charged particles (ions). These charged particles interfere with or distort transmissions of electromagnetic signals through the layer, including the transmission of GPS radio waves.

iPAQ Expansion Pack System
Allows you to personalize the appearance of your iPAQ H3000 or add extra functionality. iPAQ Style Packs offer a range of styles to customize your iPAQ, while Expansion Packs, such as the CF Card, or PC Card Expansion Pack, let you add extra features. Compaq iPAQ Expansion and Style Packs are designed to be easily slid on and off your Pocket PC without having to power off your Pocket PC first.

iPAQ Navigator/Action Button
Allows you to scroll through a list (similar to pressing the arrow keys on a keyboard). In the list view of a program, you can use your iPAQ Navigator to scroll to the item you want to view. Can also be used as game buttons within a game application. The centre of the button can be used as an Action button to open a selected item.

ISP (Internet Service Provider)
A company that provides access to the Internet. For a monthly fee, subscribers are provided with the necessary software, a username, password and access phone number. Using a modem or ISDN terminal adaptor they can then log on to the Internet, browse and download from the WWW and send and receive e-mail. An amount of free Web space is generally provided, allowing the subscriber to create a Web site and thereby have a presence on the Web.

Java
Java, Kjava, J2MEJava, formerly known as oak, is an object-oriented programming language developed by Sun. Thanks to Java™ technology, in addition to downloading ringtones, you can further enhance your phone by downloading life management tools, travel-related applications, information tools, and interactive games. When they are no longer needed, removing them is as simple as saving them.Developers can customize the user interface (UI), giving users the freedom to download the application versions they prefer. Applications can be searched using the WAP browser, and bookmarks and push messages are provided to direct the user to sites with Java applications. The possibilities are virtually limitless with Java technology, and countless application developers are using the opportunity to put their creative skills to work for the world of wireless communication. Java technology itself consists of both a programming language and a software platform, the latter of which can run on top of several operating systems. The latest Java platform to be released is known as Java 2 Platform. The version for small consumer electronics devices - such as mobile phones, Communicators, and personal data/digital assistants (PDAs) - is known as Java 2 Micro Edition (J2ME™).

Jog Dial
A dial used to scroll though the menus on certain models of PDAs and phones

Joint Precision Approach and Landing System (JPALS)
A differential GPS that will provide a rapidly deployable mobile, adverse weather, adverse terrain, day-night, and survivable precision approach and landing capability that supports joint service, civil, and multi-national interoperability.

Joint Program Office (JPO)
Part of the US DOD responsible for maintaining, managing, developing and operating the GPS NAVSTAR system.

JPALS
See Joint Precision Approach and Landing System

JPO
See Joint Program Office

Kbps
Kilobits per second (thousands of bits per second). A measure of the speed of data transmission through a communication channel.

Kilohertz
A radio signal that has 1,000 cycles per second.

Kinematic
Pertaining to motion or moving objects.

Kinematic GPS
Kinematic Positioning refers to applications in which the position of a non-stationary object (vehicle, ship, aircraft) is determined.

Knot
A unit of speed of one nautical mile per hour, equal to 1.15 statute mile per hour (1.85 kilometers per hour).

L-Band
The radio frequencies that extend from 390 MHz to 1550 MHz. The GPS carrier frequencies are in the L band (1227.6 MHz and 1575.42 MHz).

L1 Frequency 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 navigation message, and is transmitted on a frequency of 1575.42 MHz.

L2 Frequency Band
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.

LAAS
See Local Area Augmentation System

LADGPS
See Local Area DGPS

Latitude
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.

LBS
See Location Based Services

LCD
See Liquid Crystal Display

LED
Light-emitting diode. In electronics terms, a diode is a semiconductor device through which current can go in only one direction. As a side effect, light-emitting diodes produce either visible or infrared light. LEDs require very little power and are often used as indicator lights. An example of the use of LED on handheld is the light that indicates if your device is charging or not.

Leg (Route)
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.

Light Sensor
A device that detects the ambient light level so that the back-light level adjusts to suit the environment.

Lithium Battery
A soft, silvery, highly reactive metallic element that is used in batteries where weight and cold weather conditions are concerns.

Line Of Sight (LOS)
Many GPS receivers require line of sight with the satellites they are attempting to gain signals from. This means that they work less well in densely wooded areas or between tall buildings. However, new technology such as SiRFStarIII means that this is less of a problem.

Liquid Crystal Display (LCD)
A display circuit characterized by a liquid crystal element sandwiched between two glass panels. Characters are produced by applying an electric field to liquid crystal molecules and arranging them to act as light filters.
Makes small, thin screens possible.

Local Area Augmentation System (LAAS)
A specialized type of DGPS to support aircraft landings in a local area (32KM).

Local Area DGPS (LADGPS)
A form of DGPS in which the user’s GPS receiver receives real-time pseudorange and, possibly, carrier-phase corrections from a reference receiver generally located within line of sight. The corrections account for the combined effects of navigation message ephemeris and satellite clock errors (including the effects of SA), and usually, atmospheric propagation delay errors at the reference station. With the assumption that these errors are also common to the measurements made by the user’s receiver, the application of the corrections will result in more accurate coordinates.

Location Based Services (LBS)
A service which uses knowledge provided about where a user is located in order to deliver information relevant to the user's position.

Longitude
The distance east or west of the prime meridian (measured in degrees). The prime meridian runs from the north to south pole through Greenwich, England.

LORAN
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.

LOS
See Line Of Sight

Mac® OS
Apple's Macintosh® operating system.

Magnetic Deviation
The error in a magnetic compass reading caused by the difference between the true north pole and the magnetic north pole, also referred to as magnetic variation.

Magnetic North
Represents the direction of the north magnetic pole from the observer's position. The direction a compass points.

Maidenhead grid squares
A system designed to facilitate the designation of geographical positions for use within the amateur radio community.

Map Display
A graphic representation of a geographic area and its features.

Magnetic declination
The difference, in degrees, between magnetic north and true north.

Map projection
The method used to convert the spherical shape of the earth onto the plane of a map.

Map projection deformation
The error or distortion that results when the spherical shape of the earth is projected onto the plane of a map

Mask angle
The minimum acceptable satellite elevation above the horizon to avoid blockage of line-of-sight.

MCX
A type of GPS antenna connection.

Mean Sea Level
The average height of the sea surface, based upon hourly observation of the tide height on the open coast or in adjacent waters that have free access to the sea. Mean sea level, commonly abbreviated as MSL and referred to simply as 'sea level,' serves as the reference surface for all altitudes in upper atmospheric studies.

Mega
In Computer terms, Mega usually means “Million”. So, a 1 mega pixel digital camera has one million pixels.

Megahertz (MHz)
Megahertz or one million hertz. The speed of microprocessors, called the clock speed, is measured in megahertz. As an example, a Palm microprocessor running at 33MHz executes 33 million cycles per second. Each computer instruction requires a fixed number of cycles, so the clock speed determines how many instructions per second the microprocessor can execute.

Memory Stick
Memory Stick is designed by Sony for use with primarily with Sony products. It acts as an off-line connection transfer and exchange media for connecting many types of digital devices. It is a temporary storage space for pictures, music, or any other data that can be converted into digital data.

Meridian
An imaginary line circling the earth, passing through the north and south poles; a line of longitude.

MHz
See Megahertz

Microphone
A device that allows you to record voice messages.

MIPS (Millions of Instructions Per Second)
Refers to a computer processor's performance.

Microstrip Antenna
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. It is often called a patch antenna.

MMC
See multimedia card

MOB - Man Overboard
A GPS receiver function that allows marking a specific location so that you can return to that location at a later time.

Modem
A device that you connect to your computer and to a phone line, that allows the computer to talk to other computers through the phone system. Basically, modems do for computers what a telephone does for humans.

Modulation
A method of encoding a message signal on top of a carrier, which can be decoded at a later time.

Monitor Station
Station to monitor and control operation of the GPS system.

MP3
Standardised as ISO-MPEG Audio Layer-3 (IS 11172-3 and IS 138-3), MP3 employs a lossy compression technique, with bits of information being discarded to allow data to be compressed into files which are relatively small in comparison with .WAV files but which retain subjective CD quality.

Multi-Channel Receiver
A GPS receiver that can simultaneously track more than one satellite signal using a dedicated signal electronics channel for each satellite. High quality receivers may have 12 or 20 channels for L1, and another 12 channels for L2 signals. Lower quality GPS navigation receivers may have only 6 or 8 channels. In contrast to a Multiplexing Channel Receiver.

MultiMedia Card
MultiMedia Card, or MMC, is a postage stamp sized flash memory card which allows data to be stored on it. MMC cards are a means of exchanging data between PDAs, phones, digital cameras, and other devices. However, they can also act as hard drive when used on a PC or PDA to store data and software. The MMCA (MMC Association) was founded in 1998 to push the MMC standard.

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. The TV equivalent of multipath is "ghosting".

Multiplexing Channel
A channel of a GPS receiver that can be sequenced through a number of satellite signals. In contrast to a Multi-Channel Receiver in which one channel is dedicated to each satellite signal.

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.

Multimedia
Multimedia is the use of computers to present text, graphics, video, animation, and sound in an integrated way. Also the ability of a device to present various kinds of media.

NANU
See Notice Advisory to NAVSTAR Users

National Differential Global Positioning System
A network of ground and beacon based differential stations that increases GPS accuracy.

National Geodetic Survey (NGS)
An agency of the United States NOAA that defines and manages a national coordinate system. This network, the NSRS)">National Spatial Reference System (NSRS), provides the foundation for transportation and communication; mapping and charting; and a multitude of scientific and engineering applications.

National Marine Electronics Association (NMEA)
A U.S. standards committee that defines data message structure, contents, and protocols to allow the GPS receiver to communicate with other pieces of electronic equipment aboard ships.

National Spatial Data Infrastructure (NSDI)
The set of base geographic data necessary for effective operation of the United States federal government and its suppliers, made accessible as a distributed database.

National Spatial Reference System (NSRS)
A system administered by the NGS that provides the foundation for transportation and communication; mapping and charting; and a multitude of scientific and engineering applications.

Native Application
An application that comes already installed in a new handheld computer.

Nautical Mile
The unit of distance used in most maritime navigation. It is 1.15 times longer than a statute mile, and equals 1852metres, or 6076 feet.

Navigation
The act of determining the course or heading of movement. This movement could be for a plane, ship, automobile, person on foot, or any other similar means.

Navigation Message
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.

NAVSTAR
The official U.S. Government name given to the GPS satellite system. NAVSTAR is an acronym for NAVigation Satellite Timing and Ranging.

Network
Any time you connect two or more computers together so that they can share resources, you have a computer network.

NGS
See National Geodetic Survey

NMEA
See National Marine Electronics Association

NMEA 0183
The committee of the National Marine Electronics Association that developed a standard for interfacing marine electronic devices. The standard is widely used for interfacing GPS receivers.

Noise
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

Notice Advisory to GLONASS Users (NAGU)
A periodic bulletin alerting GLONASS users to changes in system performance.

Notice Advisory to NAVSTAR Users (NANU)
A periodic bulletin alerting GPS users to changes in system performance

NSDI
See National Spatial Data Infrastructure

NSRS
See National Spatial Reference System

Nokia
Nokia Corporation is one of the world's largest telecommunications equipment manufacturers. Headquartered in Keilaniemi of Espoo, Finland, this Finnish telecommunications company is best known today for its leading range of mobile phones. Nokia also produces mobile phone infrastructure and other telecommunications equipment for applications such as traditional voice telephony, ISDN, broadband access, professional mobile radio, voice over IP, wireless LAN and a line of satellite receivers.NAGU

On-the-Fly (OTF)
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.

Operating system (OS)
The software controlling the overall operation of a multipurpose computer system, including such tasks as memory allocation, input and output distribution, interrupt processing, and job scheduling.

Ordnance Survey of Great Britain (OSGB)
A system similar to the U.S. UTM for Great Britain.

Original Equipment Manufacturer (OEM)
Refers to the software or hardware manufacturer before relabelling or distribution.

OS
See Operating system

OSGB
See Ordnance Survey of Great Britain

Oscillator
A device that generates a signal of a given frequency.

Outage
Defined as a loss of GPS Availability, due to either there not being enough satellites visible to calculate a position, or the value of the DOP indicator is greater than some specified value (implying that the accuracy of the position is unreliable).

Over the Air (OTA)
The term used for downloading information or applications via WAP or web, such as ringtones, games, upgraded software or configuration.

OTA
Over the Air

OTF
On-the-Fly

P-Code
See Precision (P)-Code

Packet
A unit of data that is routed between an origin and a destination on the Internet or any other packet-switched network.

Palm Inc
Makes the Palm OS® and the line of Palm™ handheld devices and accessories. Palm, Inc. split from its parent company, 3Com, early in 2000.

Palm OS®
The operating system used on Palm™ handhelds and other third-party devices.

Parallel Channel Receiver
A continuous tracking receiver using multiple receiver circuits to track more than one satellite simultaneously.

Parallel of latitude
An imaginary line circling the surface of the earth that is parallel to the equator; a line of latitude.

Passive Matrix Display
A common LCD technology used in laptops. Passive matrix displays (DSTN, CSTN, etc.) are not quite as sharp and do not have as broad a viewing angle as active matrix (TFT) displays, but they have improved dramatically over the years. Looking head on into a passive matrix screen is not all that different than looking at an active matrix (TFT) screen. The difference is more noticeable with the viewing angle. A person looking from the side sees a dimmer image with passive matrix.

Patch antenna
An antenna based on a plated section of metal on a circuit board and its associated electronics used for receiving GPS signals.

PC Card
A PC Card is a credit card-size memory or I/O device that fits into a personal computer, usually a notebook or laptop computer. The PC Card is based on standards published by the Personal Computer Memory Card International Association (PCMCIA), an industry group organized in 1989 to promote standards for both memory and I/O integrated circuit cards.

PCMCIA
See Personal Computer Memory Card International Association

PDA
See Personal Digital Assistant

PDOP
See Dilution of Precision

Personal Computer Memory Card International Association (PCMCIA)
The PCMCIA (Personal Computer Memory Card International Association) is an industry group organized in 1989 to promote standards for a credit card-size memory or I/O device that would fit into a personal computer, usually a notebook or laptop computer. The PCMCIA 2.1 Standard was published in 1993. As a result, PC users can be assured of standard attachments for any peripheral device that follows the standard. The initial standard and its subsequent releases describe a standard product, the PC Card.

Personal Digital Assistant (PDA)
A small mobile hand-held device that provides computing and information storage for personal or business use, often for keeping calendars and address information. Some PDAs are hand-held PC with small QWERTY keyboards. Another class of device uses a touch-screen and stylus for data entry.

Phase Angle
The time difference between the same point on two different waves, usually measured in fractions of a cycle (radians or degrees).

Phase Differencing
The technique of using different GPS receivers at different locations to measure the phase angles of the carrier signal from the same satellite. These angles are compared by a communications link between the two locations if real-time operations are required.

Phase-Lock Loop
Another term for carrier-tracking loop.

Pixel
The image displayed on monitors is made up lots of dots called pixels. Collectively, the number of pixels displayed is referred to as the image's resolution, the higher the resolution, the better the image will be. A pixel on a screen is a number of red, green, and blue phosphor dots. These dots are “excited” to varying degrees by the monitor's three electron guns, and the results mix additively to generate a specific colour.

Platform
Refers to the group of hardware, software, and accessories that revolve around a particular operating system. See operating system.

PNG
See Portable Network Graphics

Pocket PC
Handheld operating system developed by Microsoft®, which also runs on third party devices.Pocket Word, Pocket Excel, Pocket Explorer, Pocket OutlookYou will notice a lot of Windows CE applications with the “pocket” designation. In general, this means that the application is a slimmed-down version of the desktop application you generally use. For example, Pocket Word has a similar look and feel to Microsoft Word; however, Pocket Word has fewer features to let it run in the smaller space provided by the Windows CE operating system.

Point Positioning
Positions calculated by a single GPS receiver without reference to other receivers or known points. Position accuracy is typically 15 to 25 metres now that selective availability has been turned off.

Port
A Port is part of the PC that is used for passing data in and out of a computing device. This is normally located on the back of the PC. The port can be a Serial Port - data is sent/received one bit at a time through a cable containing a single wire, or a Parallel port where the data is sent/received through a cable containing several pieces of wire so that more than one bit at a time can be processed. Also referred to as the I/O Port.

Portable Network Graphics (PNG)
A file format for bitmapped graphic images approved by the World Wide Web Consortium as a replacement for GIF files. GIF files use a patented data compression algorithm; PNG is patent and licence free.

Position
An exact, unique location based on a geographic coordinate system

Position Dilution of Precision (PDOP)
See Dilution of Precision.

Position error
The distance that the displayed position is off by.

Position fixing
Using a coordinate system to determine a point on a map's location

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)
The full-accuracy, single-receiver GPS positioning service provided to the United States and its allied military organizations and other selected agencies. It is based on the dual-frequency P-Code and has resistance to jamming and spoofing.

Precision (P)-Code
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.

Prime Meridian
A line of longitude at 0 degrees that runs through Greenwich, England; used as the origin for measurements of longitude.

PPS
See Precise Positioning Service

PRN code
See Pseudorandom Noise (PRN) Code

Pseudolite
A ground-based transmitter that mimics a GPS signal. These devices can be used around airports for such tasks as precision instrument landings.

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.

Pseudorandom Noise (PRN) Code
Two PRN codes are transmitted by GPS satellites: the C/A-code and P-code. Also called pseudonoise codes.
Each satellite transmits a unique C/A-Code and P-Code sequence (on the same L1 and L2 frequencies), and hence a satellite may be identified according to its "PRN number", e.g. PRN2 or PRN14 are particular GPS satellites.

Pseudorange
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.

Psion
A British handheld computer company that makes its own hardware and operating system. Utilized by the Symbian device platform.

Quadrangle
A four-sided area of the surface of the earth used as a unit in mapping.

Quadrifilar Helix Antenna
A type of GPS antenna in which four spiralling 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.

QWERTY Keyboard
QWERTY (pronounced "kwerty") is the modern-day layout of letters on most English language computer and typewriter keyboards. It takes its name from the first six letters shown on the keyboard's top row of letters.

R95
A position accuracy measure. The R95 value is defined as a circle's radius, when centred at the true position, encloses 95% of the data points in a horizontal scatter plot.

Radio Technical Committee for Maritime Applications (RTCM SC-104)
RTCM Special Committee 104 developed recommended standards for DGPS. A committee created for the purposes of establishing standards and guidance for interfacing between radio beacon-based data links and GPS receivers, and to provide standards for ground-based differential GPS stations.RTCM SC-104 recommendations define the correction message format and 16 different correction message types.

RAM (Random Access Memory)
The PC's primary storage area, used to write, store and retrieve information and program instructions which are then passed to the CPU for processing. The type of RAM used affects performance as the information stored here has to be refreshed many times per second by the processor. Manufacturers are continually coming up with new designs to provide the fastest possible access times at the lowest possible cost.

Range
A fixed distance between two points, such as between a starting and an ending waypoint, or a satellite and a GPS receiver. May also be referred to as Geometric Range.

Ranging
A technique used to determine a line of position by calculating the distance between a receiver and a known reference point.

Real-Time Kinematic (RTK)
The Relative Positioning procedure whereby carrier phase measurements (or corrections) are transmitted in real-time from a Reference or Base Station to the user's roving receiver. Centimetre accuracy is achieved without the need to record and post-process double-differenced carrier phase observables.

Receiver Autonomous Integrity Monitoring (RAIM)
A technique by which a GPS receiver system detects incorrect satellite signals by comparing solutions with different sets of satellites..

Reference Station
See Base Station

Refurbished (Factory)
Anytime a retail store or consumer opens a product in a box and it is not purchased, it cannot be sold as new. The item is then shipped back to the manufacturer to be “reconditioned”. An item purchased by a consumer and returned for any reason--perhaps the product didn’t work or the consumer simply didn’t want it--whether it's the very next day or a month later, is sent back to the manufacturer to be “reconditioned”. Some items, called “scratch and dents” have been returned to the manufacturer with visible Cosmetic wear and tear.

Relative Accuracy
The accuracy with which a user can measure position relative to that of another user on the same navigation system at the same time.

Relative Positioning
See Differential Positioning

Reliability
The ability to perform a specific function without failure under specified conditions for a given length of time.

Resolution
Resolution is a measure of graphics that are used to describe what a screen can display. A display's resolution refers to the number of pixels in the whole image, because the number of dots per inch varies depending on the screen's dimensions. For example, a resolution of 160 by 160 means that 160 lines are drawn from the top to the bottom of the screen, and each of these lines is made up of 160 separate pixels--and in turn, each dot may have any number of combinations of red, green, and blue intensities. Common resolutions in the handheld world include 160 by 160 on most Palm handhelds and 240 by 320 on most Pocket PC devices.

Receiver-Independent Exchange (RINEX )
Receiver INdependent EXchange format. A set of standard definitions and formats to promote the free exchange of GPS data and facilities. The format includes definitions for three fundamental GPS observables: time, phase, and range.

RINEX
See Receiver-Independent Exchange

ROM (Read Only Memory)
An integrated circuit chip containing programs and data that can be accessed and read but cannot be modified.

Route
A set of waypoints that define the intended path of travel.

Rover
Any mobile GPS receiver collecting data during a field session. The receiver's position may be computed relative to another, stationary GPS receiver at a Base Station. M ay also be referred to as the Mobile Receiver.

RS-232
A serial input/output standard that allows for compatibility between data communication equipment made by various manufacturers.

RTCM SC-104
See Radio Technical Committee for Maritime Applications

RTK
See Real-Time Kinematic

Satellite constellation
The arrangement in space of a set of satellites.

Scale
The distance on a map that corresponds to the same points on the earth.

SDRAM (Synchronous DRAM)
A type of DRAM designed to deliver bursts of data at very high speeds using automatic addressing, multiple page interleaving, and a synchronous (or clocked) interface. SDRAM can support bus speeds of up to 100MHz today and will probably support bus speeds of up to 200MHz in the future.

Search The Sky
A message shown when a GPS receiver is gathering satellite almanac data. This data tells the GPS receiver where to look for each GPS satellite.

Secure Digital card (SD card)
These cards combine high storage capacity, rapid data transfer, flexibility and security — all in a card sized no larger than a postage stamp. SD memory cards keep digital files secure for distribution, and are also easy to reformat, making them ideal for a wide variety of uses. The cards also hold a variety of file types, so they're as versatile as they are small.

Selective Availability (S/A)
A policy adopted by the Department of Defence to introduce some intentional clock noise into the GPS satellite signals thereby degrading their accuracy for civilian users. S/A limited the accuracy of civilian GPS systems to 300 feet or less 95% of the time. This policy was discontinued as of 1st May 2000 and now SA is turned off.

Sequential Receiver
GPS receiver in which the number of satellite signals to be tracked exceeds the number of available receiver channels. This type of receiver must sequentially step between channels to track satellites.

Serial port
This is the Port">communications port on your computer; it's also called the COM or RS-232 port. It's called serial because, although it has nine pins and many wires, the PC sends data on only one wire and receives data on one other wire. All the data bits have to follow one another on the single wire, as opposed to the parallel port, where eight separate wires transfer each bit of a byte.

Short Message Service (SMS)
(also called text messaging) A function available on digital GSM networks allowing text messages to be sent and received via the network operator to a mobile phone, or from the Internet, using an “SMS gateway” website.

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.

Sim (Subscriber Identity Module) Card.
A smart card used in the GSM system and stored inside a GSM phone. The SIM contains, among other things, subscription-related information and identification data for authentication and billing purposes.

Sim Free
Sim free products are not sold with Sim cards. They are compatible with any Sim card and do not require any additional programming or add-ons.

SiRFstarIII
With its rapid time-to-first-fix and high sensitivity, the SiRFstarIII architecture is designed to meet the rigorous demands of wireless and handheld LBS applications, and provides superior location performance, both indoors and out, for 2G, 2.5G, 3G asynchronous networks.The SiRFstarIII architecture packs a performance punch, achieving time-to-first-fix of one second for aided starts in outdoor GSM environments and acquiring signals down to -159 dBm. This makes real-time navigation practical, including in many indoor environments, through urban canyons, and under dense foliage. Unlike the lengthy sequential search process of traditional GPS architectures, the SiRFstarIII architecture, with the equivalent of more than 200,000 correlators, enables fast and deep GPS signal search capabilities, resulting in significant improvement over today’s architectures that contain a few hundred to a few thousand correlators.

SiRFXTrac
Complimenting SiRF's existing product line of GPS solutions, SiRFXTrac is a high sensitivity GPS software solution. SiRFXTrac extends the operating range in which GPS can be used - dramatically increasing the versatility of GPS-enabled products such as PDA)">personal digital assistants (PDA's), automotive navigation solutions, AVL applications, and other location aware consumer devices.If loaded with SiRFXTrac high sensitivity software, GPS-enabled mobile consumer devices will be able to continue operating in far more locations than ever before possible.

Sleeve
An attachment for a PDA which allows you to use items like network or modem cards, PCMCIA or CF cards, digital cameras, a GPS/GPRS phone, or an extra battery pack with a PDA.

Slow switching channel
A sequencing GPS receiver channel that switches too slowly to allow the continuous recovery of the data message.

Smart Card
A credit card or SIM card sized plastic card with an embedded microcircuit that contains memory, a microprocessor and an operating system controlling the use of the data or applications stored in the memory. A smart card is a secure storage place for confidential information. The most common smart card is the SIM card used in mobile phones.

Smartphone
A smartphone is generally considered any handheld device that integrates personal information management (PIM) and mobile phone capabilities in the same device. Often, this includes adding phone functions to already capable PDAs or putting "smart" capabilities, such as PDA functions, into a mobile phone.

Software
A program or set of instructions that controls the operation of a computer. Distinguished from the actual hardware of the computer.

Space Based Augmentation System (SBAS)
Any system that uses a network of geostationary satellites and ground stations to enhance the performance of a Global Navigation Satellite System (GNSS) by providing signal corrections and additional satellites with known and constant positions.

Space Segment
The satellite portion of the complete GPS system.

Speed Over Ground (SOG)
The speed at which the GPS unit and the person operating it are moving with respect to the earth's surface(ignoring tidal and current activity).

Spherical Error Probable (SEP)
A measure of accuracy in navigation. The radius of a sphere within which there is a 50 percent probability of locating a point or being located

Speaker
Sounds alarms, ringtones and plays back sound recordings.

Speed Made Good (SMG)
Required speed to destination given the current course.

Spoofing
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.

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.

Static Positioning
Location determination when the receiver’s antenna is presumed to be stationary on the earth. This allows the use of various averaging techniques to greatly improve accuracy.

Standard Positioning Service (SPS)
The GPS single receiver (stand-alone) positioning service available to any user on a continuous, worldwide basis. It is intended to provide access only to the C/A-code and the L1 carrier.

Statute Mile
A unit of length equal to 5,280 feet or 1609 metres

Straight-Line Navigation
The act of going from one waypoint to another in the most direct line and with no turns.

StrongARM
A family of high-performance RISC-based microprocessors from Intel. StrongARM chips are used in handheld devices such as PDAs and palmtops. The StrongARM technology was jointly developed by Digital Equipment Corporation and Advanced RISC Machines (ARM). In 1997, Intel acquired Digital's chip manufacturing facilities and continues to make the Alpha and StrongARM chips.

Stylus
A stylus is a pointing object that you use to navigate on a touchscreen. It works in a similar way to a mouse or trackball.

Synchronous
Refers to events that are synchronised, or co-ordinated, in time. Communication within a computer is usually synchronous and is governed by the microprocessor clock. Signals along the bus, for example, can occur only at specific points in the clock cycle.

Symbian
Symbian OS (formerly EPOC) owned by Ericsson, Panasonic, Nokia, Samsung, Siemens and Sony Ericsson. the Operating system on Smartphones by these companies.

TCP/IP (Transmission Control Protocol/Internet Protocol)
The communications protocol used by UNIX systems and the Internet. TCP checks for lost packets, puts the data from multiple packets into the correct order and requests that missing or damaged packets be resent.

TFT
Thin Film Transistor LCD panel. A type of LCD flat panel display screen in which each pixel is controlled by one to four transistors. The TFT technology provides the best resolution of all the flat panel techniques, but it is also the most expensive. TFT screens are sometimes called active matrix LCDs.

Temporal Decorrelation
The age or time lapse in corrections used in differential GPS. The longer the time lapse between the corrections, the less accurate they become.

Time To First Fix (TTFF)
Time to First Fix (TTFF) is the time it takes a GPS receiver to find satellites after the user first turns it on. This time will be shorter for a warm start where valid almanac data is still available.

Track (TRK)
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.

Triangulation
The method of determining a location on a map by using two or more points through which lines of known directions are drawn; the intersection of these lines is the desired location; can use distance and/or angles. GPS navigation uses Trilateration.

Trilateration
The same method as triangulation, except trilateration uses only distances for locating.

TOW
Time on week in seconds from midnight Saturday in UTC.

Troposphere
The portion of the atmosphere from the earth's surface to the stratosphere.

Tropospheric Delay
Retardation of GPS signals caused by elements in the troposphere such as temperature, air pressure, and water vapor.

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.

Turn (TRN)
The degrees which must be added to or subtracted from the current heading to reach the course to the intended waypoint.

Universal Mobile Telecommunications System (UMTS)
A transmission system for text, digitized voice, video, and multimedia for mobile computer and phone users no matter where they are located in the world.

Universal Transverse Mercator (UTM)
A grid coordinate system that projects global sections onto a flat surface to measure position in specific zones. These zones are 6° wide and are stepped along the equator such that each zone corresponds to a north-south strip of the earth. Coordinates are in metres as opposed to degrees, minutes, and seconds.

USB (Universal Serial Bus)
USB (Universal Serial Bus) is a plug-and-play interface between a computer and add-on devices (such as audio players, joysticks, keyboards, telephones, scanners, and printers). With USB, a new device can be added to your computer without having to add an adapter card or even having to TRN)+">turn the computer off. The USB peripheral bus standard was developed by Compaq, IBM, DEC, Intel, Microsoft, NEC, and Northern Telecom and the technology is available without charge for all computer and device vendors.
USB supports a data speed of 12 megabits per second. This speed will accommodate a wide range of devices, including MPEG video devices, data gloves, and digitizers. It is anticipated that USB will easily accommodate plug-in telephones that use ISDN and digital PBX.
Since October, 1996, the Windows operating systems have been equipped with USB drivers or special software designed to work with specific I/O device types. USB is integrated into Windows 98 and later versions. Today, most new computers and peripheral devices are equipped with USB.

USB cradle
Allows you to recharge your PDA, as well as synchronize the information between your it and a computer using software such as ActiveSync.

User Interface
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.

User Segment
That component of the entire GPS system that includes the user equipment, applications and operational procedures.

UTC (Coordinated Universal Time)
Solar time in the Greenwich Mean Time (GMT) time zone but only ever adjusted in one-second increments. Because the GPS time is different to UTC a correction factor is applied to the received time that is reported by GPS receivers in UTC.

UT1
A time scale based on Earth’s axial spin. UT1 is a measure of the true angular orientation of Earth in space. Because Earth does not spin at exactly a constant rate, UT1 is not a uniform time scale.

URL
Uniform Resource Locator. The address of web sites, documents and other resources on the World Wide Web.

Velocity Made Good (VMG)
The rate of closure to a destination based upon your current speed and course.

Vector map
Maps that use lines and polygons as opposed to pixels to display an image. Image resolution is sharp even when the image is displayed or printed at an enlarged perspective

Velocity Over Ground (VOG)
Same as Speed Over Ground (SOG) and ground speed.

VoIP
VoIP stands for Voice over Internet Protocol. A technology for transmitting ordinary telephone calls over the Internet using packet-linked routes. Also called IP telephony.

Waypoint
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.

WAN
A geographically dispersed network formed by linking several computers or local area networks (LANs) together over long distances, usually using leased long-distance lines. WANs can connect systems across town, in different cities, or in different regions of the world.

WAP
Wireless Application Protocol. A global standard for developing applications over wireless communication networks, mostly used on mobilephones. WAP features the Wireless Markup Language (WML), which was derived from Phone.com's HDML and is a streamlined version of HTML for small screen displays. It also uses WMLScript, a compact JavaScript-like language that runs in limited memory. WAP also supports handheld input methods such as a keypad and voice recognition. With the right software, a handheld can access the Internet using WAP.

Warm Start
Used to describe state where a GPS receiver is powered on and still has valid almanac data available. This shortens the time required to locate satellites and arrive at the first position solution.

Wide Area Augmentation System (WAAS)
This system provides a satellite signal to augment GPS for precision aircraft flight and landing navigation.

Wide Area DGPS (WADGPS)
A form of DGPS in which the user’s GPS receiver receives corrections determined from a network of reference stations distributed over a wide geographical area. Separate corrections are usually determined for specific error sources (such as satellite clock, ionospheric propagation delay, and ephemeris) and are applied in the user’s receiver or attached computer in computing the receiver’s coordinates. The corrections are typically supplied in real time by way of a geostationary communications satellite or through a network of ground-based transmitters. Corrections may also be provided at a later date for postprocessing collected data.

World Geodetic System 1984 (WGS-84)
A set of parameters, established by the U.S. Defense Mapping Agency, for determining geometric and physical geodetic relationships on a global scale.

Windows CE
Windows CE is based on the Microsoft Windows operating system but is designed for including or embedding in mobile and other space-constrained devices. Windows CE is a 32-bit multitasking, multithreaded operating system.

Wi-Fi
Wi-Fi (Wireless Fidelity) is the popular term for a high-frequency wireless local area network (WLAN). The Wi-Fi technology is rapidly gaining acceptance in many companies as an alternative to a wired LAN. It can also be installed for a home network. Wi-Fi is specified in the 802.11b specification from the Institute of Electrical and Electronics Engineers (IEEE) and is part of a series of wireless specifications together with 802.11, 802.11a, and 802.11g. All four standards use the Ethernet protocol and CSMA/CA (carrier sense multiple access with collision avoidance) for path sharing. The 802.11b (Wi-Fi) technology operates in the 2.4 GHz range offering data speeds up to 11 megabits per second. The modulation used in 802.11 has historically been phase-shift keying (PSK). The modulation method selected for 802.11b is known as complementary code keying (CCK), which allows higher data speeds and is less susceptible to multipath-propagation interference.

Windows Mobile
The primary OS (operating system) in the Pocket PC market is Windows Mobile. Windows Mobile replaced Windows CE in most current Pocket PCs, has much of the look and feel of Windows, and features many "pocket" versions of popular Microsoft applications, such as Pocket Word, Excel, Access, PowerPoint, and Internet Explorer. Windows Mobile can also run set-top boxes, video game systems, palm-sized devices, and other consumer electronics. The current version is Windows Mobile 5.0.

XHTML (Extensible Hypertext Mark-up Language)
A hybrid between programming languages HTML and XML – XHTML makes documents compliant with the new XML standard. XML was created by the World Wide Web Consortium (W3C) to make the two systems compatible. It is similar to HTML but is ‘extensible' because custom tags can be defined and added.

XML
Extensible Markup Language. A web page formatting tool that is used to create web pages as well as develop Palm® computing applications.

Z-Count
The fundamental GPS time unit. It is a 29-bit binary number, of which the 10 most significant bits give the binary representation of the GPS week number, and the 19 least significant bits give the time-of-week (TOW) count in units of 1.5 seconds. A truncated version of the TOW with 6-second epochs is included in the navigation message hand-over word.

Zenith
The point on the celestial sphere that is directly above the observer.

Zenith telescope
A telescope for observing stars near the zenith.

Zero Baseline
A Zero Baseline test can be used to study the precision of receiver measurements as well as the data processing software. The experimental setup involves connecting two GPS receivers to the same antenna. When two receivers share the same antenna, biases such as those which are satellite (clock and ephemeris) and atmospheric path (troposphere and ionosphere) dependent, as well as errors such as multipath cancel during data processing. The quality of the resulting “zero baseline” is therefore a function of random observation error (or noise), and the propagation of any receiver biases that do not cancel in double-differencing.