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 pre-specified 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 courseCross 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

• Zoom

• Find

• Click Stick– Press to enter– Rotate to cursor– Hold 2 sec to mark

• Pages

•Power

Press Page button to cycle through,then use click stick for options

Class Exercise

• Visit three locations:– Copy position– Calculate distances between positions