GPS Glossary - Complete Terminology Guide 2024

Who Needs This GPS Glossary?

This comprehensive GPS terminology guide is essential for:

A - C | D - F | G - M | N - S | T - Z

2D/3D Operating Mode

2D Mode: Horizontal positioning only (no elevation) requiring at least 3 visible satellites.
3D Mode: Full positioning (horizontal + elevation) requiring at least 4 visible satellites.

Datum

A mathematical model representing the size and shape of the earth. Different datums are used for different regions and mapping systems.

Desired Track (DTK)

The compass course between the "from" and "to" waypoints in a navigation route.

DGPS - Differential GPS

System that enhances GPS accuracy using ground-based reference stations broadcasting position corrections. Improves accuracy to under 10 meters.

DOP - Dilution of Precision

Measure of satellite-receiver geometry quality. Includes GDOP (Geometric), PDOP (Position), HDOP (Horizontal), and VDOP (Vertical).

DOD - Department of Defense

The United States Department of Defense that manages and controls the Global Positioning System.

Downlink

A transmission path for communication of signals and data from a communications satellite to earth.

Elevation

The distance above or below mean sea level, measured in feet or meters.

Ellipsoid

A geometric surface used to represent the earth's shape in GPS calculations, all of whose plane sections are either ellipses or circles.

Ephemeris Data

Precise orbital and clock correction parameters for each satellite. Essential for accurate position calculation and valid for several hours.

EPE - Estimated Position Error

A measurement of horizontal position error in feet or meters based on DOP and satellite signal quality factors.

ETE - Estimated Time Enroute

The time it will take to reach your destination based on present position, speed, and course.

ETA - Estimated Time of Arrival

The estimated time you will arrive at a destination based on current navigation parameters.

Frequency

The number of repetitions per unit time of a complete waveform. GPS uses L1 (1575.42 MHz) and L2 (1227.6 MHz) frequencies.

Geocaching

A high-tech treasure hunting game where participants use GPS coordinates to find hidden containers called "geocaches."

GNSS - Global Navigation Satellite System

Umbrella term for all global satellite navigation systems including GPS (USA), GLONASS (Russia), Galileo (Europe), and BeiDou (China).

GIS - Geographic Information System

Computer system capable of assembling, storing, manipulating, and displaying geographically referenced information.

Geosynchronous Orbit

Orbit where a satellite rotates around earth at the same rotational speed as earth, appearing stationary from ground observation.

GPS - Global Positioning System

Satellite-based navigation system consisting of 31+ operational satellites providing precise positioning and timing information worldwide, 24/7.

Heading

The direction in which a vehicle is moving. May differ from actual Course Over Ground due to winds, currents, etc.

Healthy

Term used when an orbiting GPS satellite is suitable for use and functioning properly.

I/O - Input/Output

The two-way transfer of GPS information with other devices like navigation plotters, autopilots, or other GPS units.

Initialization

The first time a GPS receiver orients itself to its current location and collects almanac data for faster future acquisitions.

Ionosphere

Region of earth's atmosphere (50-400 km altitude) where ionization affects GPS radio wave transmission, causing signal delays.

Invert Route

To display and navigate a route from end to beginning for purposes of returning to the route's starting point.

L1/L2 Frequencies

L1: 1575.42 MHz - carries C/A code, P-Code, and navigation message
L2: 1227.6 MHz - carries only P-Code for military use

Latitude

A position's distance north or south of the equator, measured in degrees from zero to 90. One minute equals one nautical mile.

Leg (Route)

A portion of a route consisting of a starting waypoint and a destination waypoint.

Line of Sight (LOS)

Unobstructed direct transmission path from transmitter to receiver. Critical for GPS signal reception.

Longitude

The distance east or west of the prime meridian (measured in degrees). Prime meridian runs through Greenwich, England.

Nautical Mile

Unit of length used in sea and air navigation equal to 1,852 meters (about 6,076 feet), based on one minute of arc of a great circle.

Navigation

The act of determining the course or heading of movement for planes, ships, automobiles, or persons on foot.

NAVSTAR

Official U.S. Government name for the GPS satellite system - Navigation Satellite Timing and Ranging.

NMEA - National Marine Electronics Association

Standards committee that defines data message structure and protocols for GPS receivers to communicate with other marine electronic equipment.

North Up Orientation

GPS receiver map display mode where north is always fixed at the top of the screen regardless of direction of travel.

P-Code

The precise code of the GPS signal used by the U.S. military. Encrypted and reset every seven days to prevent unauthorized use.

Position

An exact, unique location based on a geographic coordinate system calculated by the GPS receiver.

Position Fix

The GPS receiver's computed position coordinates based on satellite signals.

Pseudo-Random Code

The identifying signature signal transmitted by each GPS satellite and mirrored by the GPS receiver to separate and retrieve signals from background noise.

Pseudorange

The measured distance between the GPS receiver and the GPS satellite using uncorrected time comparisons from satellite and receiver codes.

Route

A group of waypoints entered into the GPS receiver in the sequence you desire to navigate them.

SA - Selective Availability

Intentional degradation of GPS signals for civilian use (now discontinued since May 2000).

SOG - Speed Over Ground

The actual speed the GPS unit is moving over the ground, which may differ from airspeed or nautical speed due to environmental factors.

TTFF - Time To First Fix

Time required for a GPS receiver to acquire satellite signals and calculate initial position after startup.

TracBack

Proprietary Garmin feature that converts current track log into a route to guide you back to starting position.

Track Up Orientation

GPS receiver map display mode where current track heading is always at the top of the screen.

Track (TRK)

Your current direction of travel relative to a ground position (same as Course Over Ground).

Triangulation

Method of determining location by measuring distances from multiple reference points (satellites). Fundamental principle of GPS operation.

Troposphere

The lowest region of the atmosphere where GPS signals travel, characterized by decreasing temperature with increasing altitude.

True North

The direction of the north pole from your current position, different from magnetic north due to magnetic variation.

Turn (TRN)

The degrees that must be added to or subtracted from current heading to reach the course to intended waypoint.

UTM - Universal Transverse Mercator

Worldwide coordinate projection system using north and east distance measurements from reference points. Primary system used on USGS topographic maps.

VMG - Velocity Made Good

The rate of closure to a destination based upon current speed and course.

WAAS - Wide Area Augmentation System

U.S. augmentation system that improves GPS accuracy to 1-2 meters using ground stations and geostationary satellites. Freely available across North America.

Waypoint

Geographic location stored in GPS device for navigation purposes. Can represent landmarks, destinations, or points on a route.

WGS-84 - World Geodetic System 1984

The primary map datum used by GPS. All other datums are computed as differences from the WGS-84 standard.

XTE/XTK - Crosstrack Error

The distance you are off the desired course in either direction, displayed to help maintain correct navigation path.

Key Takeaways

This comprehensive GPS glossary provides essential knowledge for anyone working with navigation technology. Understanding these terms will help you:

• Make informed decisions when purchasing GPS equipment
• Better understand your device's capabilities and limitations
• Improve your navigation and positioning accuracy
• Effectively communicate with technical professionals
• Stay updated with modern GPS technologies and trends

Bookmark this page for quick reference whenever you encounter unfamiliar GPS terminology!