Glossary - Furuno GP-1610CF Operator's Manual

Glossary

GPS Plotter
Almanac
Each GPS satellite broadcasts its own orbital
data as well as general orbital data of all other
GPS satellites. This general orbital data is
called the Almanac. The GPS receiver receives
the Almanac and decodes it to calculate the
quantity and elevation angle of satellites in
view, to know when it can receive the GPS
signal. If there is no Almanac in the receiver
it cannot fix its position. The receiver is
shipped with no Almanac, thus when it is
turned on for the first time it starts receiving
the Almanac. Each time the unit is turned on
the previous Almanac is erased and the latest
received.
Beacon receiver
The DGPS (Differential GPS) station trans-
mits a beacon signal which contains informa-
tion about GPS error. The device which
receives the beacon signal is called a beacon
receiver.
Cold start
When the GPS receiver is turned on for the
very first time, it starts receiving the Alma-
nac. This condition is called cold start. In this
condition it takes about two minutes to find
position. Once the Almanac is stored in the
GPS navigator, it takes only about 20 seconds
to find position. (The normal start-up condi-
tion is called warm start.)
Destination
A destination can be either a single destina-
tion waypoint or a series of waypoints lead-
ing to the ultimate destination. When you set
a destination, the GPS receiver provides range
and bearing data to the destination, to help
you steer to the destination along the shortest
past possible.
Differential GPS (DGPS)
The differential GPS system, consisting of
DGPS land stations and DPGS beacon re-
ceiver equipped marine vessels, further refines
the accuracy of the GPS measured position.
A DGPS land station knows its exact posi-
tion. If there is a difference between GPS po-
sition and DGPS land stations position this is
called GPS error. The DPGS station transmits
GPS error data to a beacon receiver which
relays the data to the GPS receiver. The GPS
receiver uses this data to refine the accuracy
of the GPS position (within about 10 meters
under ideal conditions).
DGPS stations are strategically located
throughout America (including Hawaii and
Alaska), Europe, Canada, Bermuda and Bra-
zil.
Estimated time of arrival (ETA)
The time at which you arrive at a destination.
Geodetic chart
A nautical chart is usually made by either
trigonometrical survey or astronomical sur-
vey and according to the geodetic chart stan-
dards of the country where it is used. The GPS
standard chart system is WGS-84.
Thus if you are using a chart different from
WGS-84, there will be error between GPS
position and nautical chart position. To get
correct position, the GPS receiver must know
what chart system you are using, to apply an
offset to GPS position.
Magnetic bearing
Bearing relative to magnetic north, with the
compass bearing corrected for deviation.
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