Transcript Global Positioning System Training Course

Laboratory 1: Navigation
1 - Navigation Basics
2 - Global Positioning System (GPS)
3 - Exercise
Latitude and Longitude
• Imaginary lines divide the globe into degrees.
• 180° of longitude East and West
• 90° of latitude North and South
Distance
•
•
•
•
1° = 60 nautical miles* (1 nmi = 1.15 mi)
1° = 60 minutes
1 minute = 60 seconds
1 second = 16 feet, 10.5 inches
1 statute mile = 5280 feet
1 nautical mile = 6072 feet
*True on Mercator Projections, lines of longitude, the equator, and great circles.
Navigation Terms and Basics
• Aid to navigation (ATON) - a device designed to
help determine a safe course, such as buoys, or beacons.
• Bearing - the direction to an object, given as a
horizontal angle from a line of reference.
• Reciprocal bearing or course - a bearing or course that
differs from the original by 180 degrees.
• Datum - a technical term for the baseline from which a chart’s
vertical measurements are made-heights of land, or depths of
water.
• Dead Ahead - a relative bearing of 000 degrees.
• Heading - The instantaneous direction of a vessel’s bow.
• Waypoint - the position on the earth’s surface that you want to go
to, or return to, in terms of latitude and longitude
Navigation Terms and Basics
• Compass Rose - A circle graduated
in degrees, clockwise from 000o at
true north to 360o.
• Knot - a speed of one nautical mile
(6076 feet) per hour.
• True North - the direction of the
geographical north pole.
• Magnetic North - the direction of the
magnetic north pole.
•
•
•
Line of Positioning (LOP) - a line of bearing to a known origin or
reference, upon which a vessel is assumed to be located.
Fix - the point where two LOPs intersect.
Dead reckoning (DR) - the practice of estimating position by
advancing a known position for course and distance run.
GPS History, Development and Satellite
System
• GPS is a satellite-based, radio-navigation
network that provides fixes in all parts of the
world day and night.
• Developed from research done at John
Hopkins University in the late 1950s by the
US Department of Defense
• It is based on 26 satellites in circular orbits
that are 10,900 miles above the earth’s
surface.
• At least 5 satellites are in “view” from one
user system at any one time.
GPS Positioning by Trilateration
• To locate a position,
GPS units need at
least 3 satellites to
obtain a two
dimensional position.
• Each satellite sends
out a position line,
which when combined
provides the correct
location or fix.
Satellites providing a fix
GPS Receivers
• From hand held to fixed
• All provide
reliable and
accurate
positions
Initializing a GPS Receiver
• The first time a GPS unit is used, it needs
to be initialized by obtaining almanac data
from the satellites
• You may need to enter location and time
• After the initialization, your GPS will work
much faster
Understanding Position Formats and
Chart Datum
• Coordinates are in latitude and longitude
with N or S representing latitude and E or
W representing longitude
• You should always check to see that your
GPS unit is using the correct datum by
looking in a local chart’s legend
GPS Accuracy
• Typical error:
– position < 10 m
– speed < 0.1 knots
• Conditions affecting accuracy:
– Position of satellites will change
slightly with time and affect
accuracy
– Overcast weather
– Obstruction of satellite to
receiver path by structures
– Trees, buildings, etc.
Poor reception in shaded area.
Differential GPS
A differential GPS is one that entails a
separate radio receiver to correct position
• Can sometimes negate selected
availability or error created by the US
government
• Reduces position error rate to < 1 m
GPS Displays
• Graphic highway or steering page
– Position is displayed as an icon in relation to
the waypoint.
• Display terms:
Bearing = Where waypoint is relative to your position
Heading = Direction you are going
Speed = Speed over ground
Distance = Distance to waypoint
Forming and Following Routes
• A route is formed by a sequence of waypoints
either previously stored or chosen while in the
field
• Routes can be followed in forward or reverse
motion
• Automatic waypoint sequencing allows one to
receive navigation information for the
subsequent waypoint, once one reaches the
present waypoint.
Track Plotters
Track plotters create routes on the basis
of time or distance intervals
Electronic Chart Plotters
• Electronic chart plotters can display
digitized charts or maps for which your
position, intended course, track or even
complete route can be shown.
• Allows you to customize chart for personal
preferences, such as un-cluttering the
display from chart symbols
Downloading CD Maps and Charts
• Some GPS units have the capability to
download digitized maps and charts from
outside sources.
• CDs are available that allow you to
download specific regions, such as the
coastlines, or states into GPS units.
Alarms and Alerts
• Arrival alarm
– Approaching waypoint
destination with a prespecified distance
• Anchor alarm
– Moves outside specified
area or circle.
• Proximity alarm
– Enter area you may want to
avoid such as a reef
• Cross tracking error
alarm
– Alerts is you travel too far
off course
Cross tracking error
Using Simulators
• Simulator mode allows you to use the
GPS without satellite information,
meanwhile simulating real world screen
outputs.
• Useful for plotting routes prior to trips
Output formats, Data collection
•
Map units for position can be reported in
decimal degrees or meters.
To export information to GIS (global
information systems) formats, data must be
collected in decimal degrees with at least 5
significant digits.
Introduction to the Magellan
“SportTrak Map” GPS
• Power and key functions
• Navigation Screens
• Waypoints (GOTO routes)
Power
and Keys
Map Screens
• Map screen has two modes:
– Display mode. Position displayed as
icon.
– Cursor mode. Cursor is displayed
and moved relative to current
position.
• Enter cursor mode with any arrow
• Return to display mode with
escape
Data Screens
(press NAV button)
• Compass
Screen.
Displays data
digitally and
graphically.
• Large data
Screen. For
easy reading
• Position
Screen.
• Road
Screen.
Satellite and Receiver Status
• Graphical display
of satellites in view.
• Signal Strength.
Saving Locations
(Waypoints)
• Menu
– Highlight “Mark”
– Press “Enter” to mark location
– Press “Enter” to save waypoint
• Use cursor and enter to create a
waypoint name.
Going to Destinations
• The GOTO key lets you
select any stored
waypoint and set a
course from your present
position.
• Press NAV key to see
data screens and course
Garmin eTREX Vista
• Pages
• Zoom
• Find
• Click Stick
– Press to enter
– Rotate to cursor
– Hold 2 sec to mark
•Power
Press Page button to cycle through,
then use click stick for options
Class Exercise
• Visit three locations:
– Copy position
– Calculate distances between positions