NAVIGATION
is the process of determining your position, plotting a course over
which you wish to travel, and steering your vessel over that course.
- POSITION is your
exact location on the Earth. For marine navigation, this is expressed as
two coordinates, latitude and longitude.
- LATITUDE is the
number of degrees you are north or south of the Equator, and lines of
latitude are sometimes called parallels.
- LONGITUDE is the
number of degrees you are east or west of the zero degrees longitude
line, which passes through Greenwich, England. Lines of longitude are
sometimes called meridians, and they all pass through both the North and
South poles.
- WAYPOINTS are
precisely specified locations on the Earth. They can be used to mark
your destination (where you want to go), or points along the route to
your destination. Each waypoint can be specified by its latitude and
longitude.
- HEADING is the
direction your boat is pointing.
- COURSE (sometimes
called TRACK) is the direction your boat is moving over the surface of
the Earth.
- BEARING is the
direction to a specific point, such as a waypoint or destination.
- GPS is short for the
Global Positioning System. It consists of 24 satellites, which transmit
radio signals that can be used to compute position, course, and speed.
- GPS RECEIVER receives
the signals from the satellites, and computes position, course, and
speed. After you turn power on, it takes anywhere from a few seconds to
a few minutes to find the GPS signals, and compute the first position
fix. The readings from a GPS receiver will have the following typical
errors:
- Position 50 meters
(164 feet)
- Speed 0.5 knots
Errors may sometimes be
much larger, when the satellite positions in the sky are not favorable,
or when the lines of sight from the satellites to the antenna are
obstructed by masts, boat structure, trees, buildings, or bridges.
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