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Trakgps - GPS Glossaire Technique Catégorie: Électrotechnique et Électronique Date & Pays: 06/11/2014, Fr Mots: 128

Statute Mile
A unit of length equal to 5,280 feet or 1,760 yards (1,609 meters) used in the U.S. and some other English-speaking countries.

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

Temps d'Acquisition
Le temps que prend un récepteur GPS pour acquérir les signaux satellites et pour déterminer sa position initiale.

Time To First Fix
(TTFF) If you have not used your GPS unit for several months, the almanac data for the satellites may be out of date. The unit is capable of recollecting this information on its own, but the process can take several minutes. Time to First Fix (TTFF) is the time it takes a GPS receiver to find satellites after the user first turns it on (when the GPS receiver has lost memory or has been moved over 300 miles from its last location).

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.

Transducer
A device, much like a microphone, that converts input energy of one form into output energy of another. Fishfinders separate and enhance the information received from a transducer to show underwater objects.

Triangulation
A method of determining the location of an unknown point, as in GPS navigation, by using the laws of plane trigonometry.

Troposphere
The lowest region of the atmosphere between the surface of the earth and the tropopause, characterized by decreasing temperature with increasing altitude. GPS signals travel through the troposphere (and other atmospheric layers).

True North
The direction of the north pole from your current position. Magnetic compasses indicate north differently due to the variation between true north and magnetic north. A GPS receiver can display headings referenced to true north or magnetic north.

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

Universal Transverse Mercator
(UTM) A nearly worldwide coordinate projection system using north and east distance measurements from reference point(s). UTM is the primary coordinate system used on U.S. Geological Survey topographic maps.

Uplink
A transmission path by which radio or other signals are sent from the ground to an aircraft or a communications satellite.

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
The segment of the complete GPS system that includes the GPS receiver and operator.

UTC
See Coordinated Universal Time.

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

Waterproof
Some GPS units are waterproof in accordance with IEC 529 IPX7. IEC 529 is a European system of test specification standards for classifying the degrees of protection provided by the enclosures of electrical equipment. An IPX7 designation means the GPS case can withstand accidental immersion in one meter of water for up to 30 minutes. An IPX8 designation is for continuous underwater use.

Wavelength
The distance between points of corresponding phase of two consecutive cycles of a wave.

Waypoints
Waypoints are locations or landmarks worth recording and storing in your GPS. These are locations you may later want to return to. They may be check points on a route or significant ground features. (e.g., camp, the truck, a fork in a trail, or a 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.

WGS-84
World Geodetic System, 1984. The primary map datum used by GPS. Secondary datums are computed as differences from the WGS 84 standard.

Wide Area Augmentation System
(WAAS) A system of satellites and ground stations that provide GPS signal corrections for better position accuracy. A WAAS-capable receiver can give you a position accuracy of better than three meters, 95 percent of the time. (At this time, the system is still in the development stage and is not fully operational.) WAAS consists of approximately 25 ground reference stations positioned across the United States that monitor GPS satellite data. Two master stations, located on either coast, collect data from the reference stations and create a GPS correction message. For more information, see What is WAAS ?, or visit the FAA's website.

XTE/XTK
See Crosstrack Error.

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
One of the two radio frequencies transmitted by the GPS satellites. This frequency carries the Coarse Acquisition Code (C/A code), P-Code, and the nav message, and is transmitted on a frequency of 1575.42 MHz.



L2 Frequency
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.

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.

Y-Code
The encrypted P-Code.