Acquisition Time
Amount of time required for a GPS unit to lock onto
3 satellites to provide a 2D fix (latitude and longitude) of present position.
Altitude (ALT)
Your height above sea level.
Bearing (BRG)
The precise compass direction (in degrees) from your present position to
the next waypoint. (Readings are selectable in either degrees magnetic
or true north).
Clock
Your local time.
Cold Start
The process of powering up a new GPS receiver for
the first time and having it search out and lock onto the satellites by
itself, without the benefit of initialization
data. This procedure is slower and may require several minutes for initial
satellite acquisition.
Course
Deviation Indicator (CDI)
Shows your distance to the side of the desired course line.
Course
Over Ground (COG)
The current direction (in degrees) that you are actually traveling.
(Selectable in degrees magnetic or true
north)
Cross
Track Error (XTE)
Digital reading on GPS steering screens that indicates
precisely how far off you are, to the right or left of the center of the
course.
Differential GPS (DGPS)
A system devised initially by the U.S. Coast Guard that is now an
international maritime standard to improve GPS accuracy
levels to be within 10 meters. It employs a land based, fixed position,
DGPS reference receiver to first calculate any basic GPS errors (and
previously Selective Availability
errors). It then transmits the necessary correction factors to mobile GPS
receivers in the area. DGPS does require an added beacon receiver to
communicate with the standard GPS unit.
Distance (DIS)
Distance remaining between your present position and a waypoint.
Distance To Go(DTG)
Digital readout (selectable in miles, nautical miles, or kilometers)
displayed only when navigating to a waypoint. It
simply indicates the remaining distance from your present position to the
next waypoint.
DNT_UPT
Count down-timer (DNT) - Starts at a user setting and counts
down to zero. Useful for setting a time limit for travel. Count
up-timer (UPT) - Starts at zero and counts upwards. Useful as a
measure of elapsed time of travel.
Estimated Position Error (EPE)
An estimation of the accuracy of your position that tells you how far off
target your unit might be. This calculation is based on the geometry and
position of tracked satellites, time clock offset, satellite signal
quality, and more.
Estimated Time En-Route (ETE)
An estimation of the time required to travel to a pre-selected waypoint
or the next waypoint in a route. This calculation is based on the
speed and direction of travel towards the selected waypoint.
Event Marker
A graphic symbol that can be placed on the plotter
display (and saved in memory) to represent some special event or area
of interest to the GPS user. Also known as Icon.
Fix
A measure of your receiver's position quality. A fix of 1 is
poor, 9 is best
Global Positioning
System (GPS)
The Global Positioning System (GPS) is a "constellation" of 24
well-spaced satellites that orbit the Earth and make it possible for
people with ground receivers to pinpoint their geographic location. GPS
location accuracy is within 20 meters. Location accuracy can be boosted
through the use of Wide Area Augmentation System (WAAS)
or Differential GPS (DGPS). The GPS is
owned and operated by the U.S. Department of Defense but is available for
general use around the world.
Ground Speed (GS)
Your actual speed; your speed relative to the ground being traversed in a
given amount of time.
Icon
A graphic symbol that can be placed on the plotter screen (and saved
in memory) to represent some special event or area of interest to the GPS
user. Also known as Event Marker.
Initialization
Refers to the procedure of telling a new GPS
receiver where it is, when it is turned on for the first time. Information
required for initialization includes approximate present
position in latitude/longitude coordinates, the current local time and
date.
Magnetic North
Magnetic north is the location our compasses point to; it lies several
hundred miles to the south of true north, at a
location in Canada.
Map Datums
Since the earth is not flat a method must be used to create a
"flat map" from a round earth. Maps and charts are based on a
survey of the area that's covered by the map or chart. These surveys are
called "Datums". Maps that are created using different datums
will show the same latitude/longitude in slightly different locations.
Different datums are based on different mathematical models of the earth's
shape and dimensions (ELLIPSOIDS) plus an additional factor of PROJECTION.
MGRS (Military Grid Reference System)
An alphanumeric version of a numerical UTM (Universal
Transverse Mercator) grid coordinate.
Multiplexing Receiver
GPS receiver that rotates a small number of
channels to multiple satellites in order to provide current positioning
data. Typically, multiplexing receivers require more time for satellite
acquisition and lock on, and are not as accurate as parallel channel
receivers. Multiplexing receivers are also more prone to lose satellite
fix in dense woods compared to parallel
channel GPS receivers.
Parallel-Channel Receiver
GPS receiver that simultaneously tracks multiple
satellites to provide the fastest, most reliable and accurate navigational
data...under the severest of environmental conditions.
Pixels
These are "picture elements," or little squares of color
that come together to form shapes and images on a liquid crystal display
(LCD). The more pixels per square inch, the sharper and more detailed
picture you see.
Plotter Display
Provides an overhead "bird's-eye" view of your current
position, relative to the waypoints and event
marker/icons you've saved. A dotted-line marks
the shortest route to the chosen waypoint, and a
recorded plot-trail indicates the path you've taken so far.
Position Display
One of the primary navigational data screens that emphasizes the
present position latitude/longitude coordinates, as well as other helpful
information.
Present Position
Current location on the face of the Earth, in terms of the specific
latitude/longitude coordinates, displayed in degrees/minutes/&
thousandths of a minute.
Programmable Windows
The ability to customize existing split-panel window groupings with
the specific combination of navigational data preferred.
Route
Consists of two or more waypoints combined in
a course of travel. It provides the automatic capability to navigate
through several waypoints, without having to reprogram the unit after
arriving at each one. Once programmed into the GPS
unit, the route provides the option of navigating forward through the
waypoints or in reverse order.
Satellite Status Display
An information screen that shows technical data about each satellite in
view. Information includes receiver channel numbers; actual satellite I.D.
numbers; status of satellite tracking (T) or searching (S); satellite
elevations and azimuths; signal-to-noise ratios (higher the number, the
better); and dilution of precision ratings (GDOP is most important;
smaller the number, the better).
Savable Plot Trails
The capability to save the actual trail created on the plotter
display, thereby enabling the GPS user to either
backtrack the course immediately...or retrace the trip at a later time.
Selective Availability (S/A)
The system used by the U.S. Department of Defense prior to May 1, 2000 to
intentionally degrade the accuracy of satellite GPS
signals being transmitted to civilian GPS receivers. Until recently, all
brands of civilian GPS receivers were equally affected by S/A. With random
S/A on, the government had agreed that civilian GPS accuracy levels would
consistently be 100 meters or less, 95% of the time. Now that S/A
restrictions have been lifted, accuracy levels have improved to 20 meters
or less.
Speed Over Ground (SOG)
Digital reading that indicates your current ground
speed. (Selectable in miles-per-hour, knots, or kilometers-per-hour)
Steering Screen
Shows a graphic, highway view of the GPS
user's Course Over Ground. Provides
helpful instructions as to how far off-course...which direction to steer,
right or left, to make corrections...and displays related nav-data
pertaining to the waypoint.
Straight Line Navigation
The standard method of navigation used by recreational GPS
products. When commanded to navigate to a waypoint,
the unit draws a straight, dotted line from the present position to the
selected waypoint. It's the shortest, most direct route to the
destination. Caution: Straight line navigation does not take into account
any obstacles in the path; interim waypoints may be required to navigate
safely around obstacles
Time To Go (TTG)
Digital reading showing the time remaining from your current position to
the next waypoint. This function takes into
account your Distance To Go (DTG), and your Velocity
Made Good (VMG) to give you as closely as possible the amount of time
left to reach your waypoint. Displayed in hours, minutes, and seconds, it
will continue counting down until waypoint is reached.
Track (TRK)
The direction you are traveling.
True North
True north is the top of the world, where all lines of longitude
converge; not to be confused with magnetic north.
UTC
Coordinated Universal Time. Time at the prime meridian at
Greenwich, England. Formerly known as GMT.
UTM (Universal Transverse Mercator)
Universal Transverse Mercator (UTM) coordinates define two-dimensional,
horizontal positions. Each ZONE in UTM is given a number from 00 to 59
starting at the International Date Line and progressing east. UTM also
divides each zone horizontally as well. These divisions start at the
equator and are 8 degrees wide. The first half of the alphabet is used for
the Southern Hemisphere while the second half is used for the Northern
Hemisphere. Thus a point just above the hemisphere would be the letter N
proceeding to the letter X at the north pole, while just below it would be
an M and proceeding backwards to the letter C at the south pole.
Velocity Made Good (VMG)
Digital speed reading, similar to Speed Over
Ground (SOG), that compensates for progress being made toward a waypoint.
For example, when traveling directly on course toward a waypoint, the SOG
and VMG readings may match. However, when traveling off course, the VMG
reading will typically be slower than the SOG. VMG is a true indication of
the speed being made to the selected waypoint.
Volts
Electrical system voltage.
Waypoint
Location, spot, or destination (latitude/longitude) that can be stored
in memory to be recalled and used at a later time for navigation purposes.
Simply think of it as an electronic address.
WAAS - (Wide Area Augmentation System)
A satellite navigation system designed by the U.S. Federal Aviation
Administration (FAA) to boost the accuracy of GPS
satellite navigation. Improvements in accuracy are approximated to be
within 7 meters. Note: Currently, WAAS is not fully implemented. It was
created for aviation applications. It uses geostationary satellites over
the equator, which makes WAAS signals easily blocked in North America by
terrain obstructions. Users may experience temporary loss of WAAS support,
especially in wooded areas.
