Introduction togps shsm

Introduction to GPS

SHSM Certificate

Welcome!

The purpose of this tutorial is to introduce you to the theory behind Global Positioning Systems and their safe use.

Although the information provided here is essential for anyone using a GPS in the field, there is no substitute for hands on training.

Please obtain training from a qualified instructor before entrusting your safety to a GPS unit!

Even in relatively mild weather Even in relatively mild weather conditions, conditions,

becoming “lost” overnight can result becoming “lost” overnight can result potentially deadly hypothermiapotentially deadly hypothermia, ,

not to mention panic, dehydration, not to mention panic, dehydration, increased chance of injury, increased chance of injury,

bumping into “unfriendly” animals…or bumping into “unfriendly” animals…or eveneven

paying the cost of the “rescue” paying the cost of the “rescue” operation.operation.

There is a reason why this is the first message you see when you turn a GPS on!

The Global Positioning System provides convenient and accurate information, as long as you remember the basics and are aware of the limitations.

Like all technology GPS is not perfect. Always be prepared (and able!) to use alternate means to find your way home!

A Bit of Background…

Global Positioning Systems were first established by the United States Department of Defense.

While initially a military system, it was always intended to be used in part by civilians.

The project became fully active in the mid 1990’s, but with degraded accuracy for civilian users (about 100 metres)

On May 1, 2000, the accuracy of signals for civilian users was upgradedand practical applications for the technology were quickly found.

Some of these applications are:field navigationmap makingsurveyingsearch and rescuegeo-caching

MAPMAP

COMPASSCOMPASSGPSGPS

3 Key “Technologies”

The safest and most effective way to use GPS is to integrate it with older “technologies”.

Map reading skills and the ability to navigate with a magnetic compassare critical. And don’t forget to take them along with you!

Magnetic Compass vs GPS

Compass

Pro ConNo batteries Magnetic field

is not uniform

Easy to use with training

Unreliable in polar areas

Magnetic pole moves

Minerals in the ground cause deflections

Not as accurate as GPS

GPS

Pro ConAccuracy Batteries die

Easy to use with training

Several types of error

Multiple functions (course storage, speed read out, altitude)

Requires more training

On board map

Not affected by environment

http://www.oceanservice.noaa.gov/topics/navops/positioning/welcome.html

An Artificial Constellation…

The GPS constellation consists of 24 satellites, orbiting at about 20,000 km above the earth.

At any time, on any point on the surface of the earth, an average of 9 satellites are visible to GPS receivers.

A series of ground stations keep track of the satellites and ensure the signals are accurate.

Most GPS receivers use signals from 4 satellites to generate their position information.

Imagine being in a very large room with an alarm clock.

When the alarm goes off, the sound travels to your ear.

If you were able to measure the time it takes for the sound to reach your ear, you could calculate how far away the clock was.

An Alarming Analogy…


With a single alarm clock, the distance that you calculate is the radius of a circle you are standing on.

The problem is that you have no idea where exactly on the circle you are.


Add a second alarm clock and you can narrow your location to 2 possible points where the circles intercept (see below).

Good, but not perfect.


Adding a third alarm clock to the equation produces only one possible location.

The precision of that position will depend on a few things, such as the accuracy of the clocks, how carefully you measure the time, or how well you can do the calculations.

Since few things are perfect, you will not be able to calculate the exact position.

BUT, you can get to within a reasonable (and useable) distance from the exact location.


Although it is a bit simplistic, the analogy is actually closer than you may think.

GPS relies on a series of very accurate atomic clocks. Distances are calculated by measuring how long it takes for a signal to get from the satellites to the receiver.

The GPS unit in your hand receives signals from the satellites and performs the calculations.

In general it will pick the best signals to generate the most accurate location.

A fourth signal will give reasonably accurate elevation information.

Three clear signals will provide accurate two dimensional position.

The GPS will show you which satellites it is tracking and how strong the signals are.

The Reality…

Satellites transmit a radio signal with precise time information.

The Reality…

A typical handheld GPS unit used in field navigation will provide the user with 3 to 5 metres of accuracy under ideal conditions.

The WRDSB currently uses the Garmin ETREX and Garmin ETREX Legend GPS’s.

They are typical entry level units and allow a trained user to navigate safely.

They will be discussed in moredetail in the third section of this tutorial.

They are subject to the errors andlimitations that will be outlined in the next section.

Quiz 1 here

GPS Errors

GPS provides rapid and accurate position informationwith some limitations. You must be aware of these limitationsIf you are going to navigate effectively.

The following slides outline the major sources of error encountered when using GPS technology.

Signal multipathSignal multipath — This occurs — This occurs when the GPS signal is reflected off when the GPS signal is reflected off objects such as tall buildings or large objects such as tall buildings or large rock surfaces before it reaches the rock surfaces before it reaches the receiver. This increases the travel time receiver. This increases the travel time of the signal, thereby causing errors.of the signal, thereby causing errors.

GPS Errors

Receiver clock errorsReceiver clock errors — A receiver's built-in clock — A receiver's built-in clock is not as accurate as the atomic clock onboard the GPS is not as accurate as the atomic clock onboard the GPS satellites. Therefore, it may have very slight timing errors.satellites. Therefore, it may have very slight timing errors.

This will affect the accuracy of the calculated position.This will affect the accuracy of the calculated position.

11:59:36.25478

GPS Errors

Orbital errorsOrbital errors — Also known as — Also known as ephemeris errorsephemeris errors, these , these are inaccuracies of the satellite's reported location.are inaccuracies of the satellite's reported location.

GPS Errors

Ionosphere and troposphere Ionosphere and troposphere delaysdelays — The satellite signal slows as it — The satellite signal slows as it passes through the atmosphere. The GPS passes through the atmosphere. The GPS system uses software that calculates an system uses software that calculates an average amount of delay to partially correct for average amount of delay to partially correct for this type of error.this type of error.

GPS Errors

Number of satellites Number of satellites visiblevisible — The more satellites — The more satellites a GPS receiver can "see," the a GPS receiver can "see," the better the accuracy. Buildings, better the accuracy. Buildings, terrain, electronic interference, or terrain, electronic interference, or sometimes even dense foliage sometimes even dense foliage can block signal reception, can block signal reception, causing position errors or causing position errors or possibly no position reading at possibly no position reading at all. all.

GPS units typically will not work GPS units typically will not work indoors, underwater or indoors, underwater or underground.underground.

GPS Errors

Satellite geometrySatellite geometry— — This refers to the relative This refers to the relative position of the satellites at any position of the satellites at any given time. given time.

Poor geometry results when the Poor geometry results when the satellites are located in a line or satellites are located in a line or in a tight grouping.in a tight grouping.

Ideal satellite geometry exists Ideal satellite geometry exists when the satellites are located when the satellites are located at wide angles relative to each at wide angles relative to each other. other.

GPS Errors

Intentional degradation of the Intentional degradation of the satellite signalsatellite signal — Selective — Selective Availability (SA) is an intentional Availability (SA) is an intentional degradation of the signal once imposed by degradation of the signal once imposed by the U.S. Department of Defense. the U.S. Department of Defense.

SA was intended to prevent military SA was intended to prevent military adversaries from using the highly accurate adversaries from using the highly accurate GPS signals. GPS signals.

The government turned off SA in May The government turned off SA in May 2000, which significantly improved the 2000, which significantly improved the accuracy of civilian GPS receivers. accuracy of civilian GPS receivers.

GPS Errors

GPS Errors FIX

Some systems (ETREX Legend included) experience “software glitches” when WAAS is enabled! Be careful.

Think of WAAS as an electronic “tune up” for GPS.

Newer GPS units (including our Garmin ETREX Legend) have software enabling them to use WAAS.

Accuracy can be boosted to 1 meter!

Wide Area Augmentation System (WAAS)

Quiz 2 here

Features and Operation of a Typical GPS

There are a multitude of GPS receivers available. The cost of an entry level unit is around the $100 mark.

Common accessories include download cables, computer mapping software, and various unloadable map packages.

Regardless of the model you use most will have the same general features described on the next few slides.


The Garmin ETREX Legend is typical of the entry level GPS unit you may encounter.

Some of its features include:• 22 hours operation on 2 AA batteries• water resistant to 1 metre for 30 minutes• can track up to 12 satellites• contains a North America base map• can hold up to 500 waypoints

The Main Pages

Most GPS units display information on a set of main pages. These pages include:

Main Menu Page Satellite Page

Map PageCompass PagePosition Page

MAIN MENU PAGES

Garminetrex

Garmin12

Garminetrex Vista

GarminEtrex LEGEND

The main menu is the starting point when you turn your GPS on.

SATELLITE PAGES

This is where you check to see if you have an adequate signal to use the GPS.The outer circle is the horizon, the inner circle is 45o up,

and the dot in the centre is straight up.The numbers in the circle correspond to the numbers in the bar diagram.

GarminEtrex

Garmin12

Garminetrex Vista

Garmin60

GarminEtrex LEGEND

MAP PAGES

Some GPS units come with maps, others require a map to be uploaded to the unit.

Use the zoom option to change the scale of your map.Use the pan option to look at the off-screen parts of the map.

Set your map to North Up or Track Up.

Garminetrex

Garmin72

Garmin60

TRAKMAPS

GarminEtrex LEGEND

COMPASS PAGESThis is the screen you use to navigate to a chosen waypoint.

You can usually manipulate the data fields to show what you want.The arrow shows you the direction to travel (straight line)

You have to start moving to get the arrow to point the right way.

Garminetrex

Garmin12

Garmin60

Garmin60c

GarminEtrex LEGEND

POSITION PAGES

On many units, your position is given right on the Satellite Page.The accuracy of these coordinates will depend on satellite reception.

Position will likely be wrong if your map datum isn’t set properly.

Garminetrex

Garmin12

Garminetrex Vista

Garmin60

GarminEtrex LEGEND

GARMIN

ETREX

GARMIN ETREX Legend


The WRDSB currently uses two types of GPS. Both are entry level units that have proven to be very reliable and accurate.


GARMIN

ETREX

POWER BUTTON

PAGE BUTTON…press to move through 5 screens.

SCROLL BUTTONS…move up or down menus

ENTER BUTTON…press to select an item.


GARMIN

ETREXLegend

POWER BUTTON

PAGE BUTTON…press to move through 5 screens.

SCROLL BUTTONS…move up or down menus

ENTER BUTTON…press to select an item.

THUMB STICK….press to enter, scroll, hold to mark.

Setup Menus

The Setup Menu can usually be found on the Main Menu page.

The setup menu is where you accessall the various settings which you needto know about to properly operate your

GPS.

GARMINETREX

GARMINETREXLegend

GPS Settings

POSITION FORMAT: Allows you to chose the co-ordinate system you want to use.

MAP DATUM: Make sure this matches the map you are using!.

DISTANCE, SPEED, DEPTH: Set this to whatever matches your map.

Navigating

Theory is a poor substitute for hands on experience when it comes to GPS.

Navigation with the GPS is fairly simple and can be learned easily.

In its simplest terms, navigation is simply a case of following the needle on the GPS to a WAYPOINT.

WAYPOINTS can either be marked with the GPS unit, or uploaded from some other source such as an electronic database or a map.

To MARK a WAYPOINT, select “Mark” on the appropriate menu, then verify it by clicking “OK”.

The WAYPOINT can also be edited (values changed) to make it a new location. If you can text, this will be a snap.

To navigate to a chosen point, select it and click on “Goto”. Start walking and follow the arrow!

Navigating

Always remember that the GPS does not replace common sense.

It will ALWAYS SHOW YOU THEALWAYS SHOW YOU THE STRAIGHT LINE STRAIGHT LINE ROUTEROUTE…

not the BEST ROUTEBEST ROUTE or the SAFEST ROUTESAFEST ROUTE!

A

B

Congratulations…you’re done!

The preceding slides have introduced you to the theory and some of the features of a basic GPS unit.

Remember that the GPS unit is only one part of the equipment you should carry for field navigation.

You should seek qualified hands on instruction with a GPS unit prior to using it in the field.

And always remember that GPS is a navigation AID, not a substitute for common sense and proper training.

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Introduction togps shsm