The Glossary Of GPS(5)

The Glossary Of GPS Between M-P

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

Magnetic Variation
In navigation, at a given place and time, the horizontal angle (or difference) between true north and magnetic north. Magnetic variation is measured east or west of true north.

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

Mean Sea Level
The average level of the ocean's surface, as measured by the level halfway between mean high and low tide. Used as a standard in determining land elevation or sea depths.

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 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.

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, especially an international and U.S. unit equal to 1,852 meters (about 6,076 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.

NMEA (National Marine Electronics Association)
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.

NMEA Standard
A NMEA standard defines an electrical interface and data protocol for communications between marine instrumentation.

North Up Orientation
Fixes the GPS receiver’s map display so north is always fixed at the top of the screen.

PanTrack™
A Garmin-proprietary feature that allows the user to move the pointer and pan a track in either direction, then select a location along the track to start a TracBack® or GoTo, or to mark a waypoint.

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

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.

Pixel
A single display element on an LCD screen. The more pixels, the higher the resolution and definition.

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

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.

Prime Meridian
The zero meridian, used as a reference line from which longitude east and west is measured. It passes through Greenwich, England.

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.

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.