| Term |
Definition |
Accuracy |
A measure of how close an estimate of a GPS position is to the true location. |
Acquisition Time |
The time it takes a GPS receiver to acquire satellite signals and determine the initial position. |
Active Antenna |
An antenna that amplifies the GPS signal before sending it to the receiver. |
Active Leg |
The segment of a route currently being traveled. A "segment" is that portion of a route between any two waypoints in the route. |
Almanac Data |
Information transmitted by each satellite on the orbits and state (health) of every satellite in the GPS constellation. Almanac data allows the GPS receiver to rapidly acquire satellites shortly after it is turned on. |
Altimeter |
An instrument for determining elevation |
Analog Signal |
The principal feature of analog signals is that they are continuous. In contrast |
Anti-Spoofing |
Encryption of the P-code to protect the P-signals from being "spoofed" through the transmission of false GPS signals by an adversary. |
Atomic Clock |
A very precise clock that operates using the elements cesium or rubidium. A cesium clock has an error of one second per million years. GPS satellites contain multiple cesium and rubidium clocks. |
AutoLocate® |
This is a proprietary feature of Garmin GPS receivers. A Garmin unit displays the "AutoLocate" status when it is looking for and collecting data from satellites that were visible at its last known or initialized position (almanac data) |
Azimuth |
The horizontal direction from one point on the earth to another |
Basemap |
Garmin mapping units come with permanently built-in basemaps |
Beacon |
Stationary transmitter that emits signals in all directions (also called a non-directional beacon). In DGPS |
Bearing |
The compass direction from a position to a destination |
Bluechart |
Mapping software of the sea/ocean. |
Bluetooth |
Wireless connectivity. |
C/A Code |
See Coarse/Acquisition Code. |
Carrier Frequency |
The frequency of an unmodulated output of a radio transmitter. The GPS L1 carrier frequency is 1575.42 MHz. |
Cartography |
The art or technique of making maps or charts. Many GPS receivers have detailed mapping—or cartography— capabilities. |
CDI |
See Course Deviation Indicator. |
CDMA |
See Code Division Multiple Access. |
Clock Bias |
The difference between the indicated clock time in the GPS receiver and true universal time (or GPS satellite time). |
Clock Offset |
A constant difference in the time reading between two clocks |
CMG |
See Course Made Good. |
Coarse/Acquisition Code (C/A Code) |
The standard positioning signal the GPS satellite transmits to the civilian user. It contains the information the GPS receiver uses to fix its position and time |
Code Division Multiple Access (CDMA) |
A method whereby many radios use the same frequency |
COG |
See Course Over Ground. |
Cold Start |
The power-on sequence where the GPS receiver downloads almanac data before establishing a position fix. |
Control Segment |
A worldwide chain of monitoring and control stations that control and manage the GPS satellite constellation. |
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. |
Coordinates |
A set of numbers that describes your location on or above the earth. Coordinates are typically based on latitude/longitude lines of reference or a global/regional grid projection (e.g. |
Course |
The direction from the beginning landmark of a course to its destination (measured in degrees |
Course Deviation Indicator (CDI) |
A technique for displaying the amount and direction of crosstrack error (XTE). |
Course Made Good (CMG) |
The bearing from the 'active from' position (your starting point) to your present position. |
Course Over Ground (COG) |
Your direction of movement relative to a ground position. |
Course To Steer |
The heading you need to maintain in order to reach a destination. |
Course Up Orientation |
Fixes the GPS receiver's map display so the direction of navigation is always "up." |
Crosstrack Error (XTE/XTK) |
The distance you are off the desired course in either direction. |
