The Glossary Of GPS(3)

The Glossary Of GPS Between D-F

Datum
A math model which depicts a part of the surface of the earth. Latitude and longitude lines on a paper map are referenced to a specific map datum. The map datum selected on a GPS receiver needs to match the datum listed on the corresponding paper map in order for position readings to match.

DCG®
See Depth Controlled Gain.

Depth Controlled Gain (DCG)
A Garmin proprietary technology that automatically adjusts fishfinder sensitivity according to depth, not echo intensity. The result is a much more detailed and accurate picture of bottom structure.

Desired Track (DTK)
The compass course between the "from" and "to" waypoints.

DGPS
See Differential GPS.

Differential GPS (DGPS)
An extension of the GPS system that uses land-based radio beacons to transmit position corrections to GPS receivers. DGPS reduces the effect of selective availability, propagation delay, etc. and can improve position accuracy to better than 10 meters.

Dilution Of Precision (DOP)
A measure of the GPS receiver/satellite geometry. A low DOP value indicates better relative geometry and higher corresponding accuracy. The DOP indicators are GDOP (geometric DOP), PDOP (position DOP), HDOP (horizontal DOP), VDOP (vertical DOP), and tdOP (time clock offset).

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

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

DOP
See Dilution Of Precision.

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

DTK
See Desired Track.

Elevation
The distance above or below mean sea level.

Ellipsoid
A geometric surface, all of whose plane sections are either ellipses or circles.

Ephemeris Data
Current satellite position and timing information transmitted as part of the satellite data message. A set of ephemeris data is valid for several hours.

EPE
See Estimated Position Error.

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.

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.

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

ETA
See Estimated Time Of Arrival.

ETE
See Estimated Time Enroute.

Frequency
The number of repetitions per unit time of a complete waveform, as of a radio wave (see L1 and L2 frequencies in this glossary).