Global Positioning SystemsGPS

GPS Navigation

•Global Positioning Satellite Navigation

•Garmin GPS 72•Topographic Maps•Aerial

Photography

What is GPS?

• The Global Positioning System is a network of 24 satellites placed into orbit by the U.S. Department of Defense. The satellites circle the earth twice a day in a very precise orbit and transmit information to earth. The orbits are arranged so that at any time, anywhere on Earth, there are at least four satellites "visible" in the sky.

GPS History

•Development began during the “space race” of the 1950s and 1960s

On October 4, 1957, the Soviet Union launched

Sputnik I. The world's first artificial satellite, it was

about the size of a basketball, weighing only 183 pounds. It took about

98 minutes to orbit the Earth on its elliptical path.

Official Name:

Iskustvennyi Sputnik Zemli

(fellow world traveler of the earth)

Laika, the first living creature in space,

traveled on Sputnik II

Sputnik II was launched on November 3, 1957, allowing them to continue their work.

GPS History

• The ability to determine a satellites orbit from the ground by using radio signals was the first step in developing an accurate space-based positioning system.

• Navy used this information to develop the world ’s first satellite navigation system: Navy Navigation Satellite System (TRANSIT)..

• Final constellation consisted of three operating and three spare satellites in a 600-nautical-mile polar orbit, three ground control stations, and receivers on naval vessels

• Terminated service on December 31, 1996 (replaced by GPS).

GPS History

• In the mid-1960's, the Air Force also initiated a program consisting of several satellites which would accurately determine the position of a vehicle moving on land or in the air.

• In 1973, the Navy and the Air Force programs combined to form a system called the Navigation System with Timing and Ranging (NAVSTAR) – which became known as the Global Positioning System (GPS).

GPS History

• GPS satellites continued to be launched to complete the GPS constellation.

• GPS satellites were payloads of the NASA Space Shuttle flights of the early 1980s.

• Launches suspended because of the Challenger accident in 1986.

GPS History

• Constellation development continued into the 1990s.

• In 1991 GPS was first used in combat during Operation Desert Storm.

• Public awareness of GPS increases during the war.

• System reached full operational capability on July 17, 1995.

• Increasing use within the private sector.

GPS History

• Approximately 1.4 million civilian GPS receivers have been produced each year since 1997

• GPS created an economic impact of $6.2 billion in 2000. 

• Future expectations project that the economic impact of GPS technology may surpass $50 billion by the end of this year.  

How GPS Works

•The GPS “system” actually includes three separate segments:▫Space▫Control ▫User

Space Segment

• GPS satellites are not in geo-synchronous (stationary) orbit, but instead circle the Earth at altitudes of 10,900 nautical miles (approx. 12,500 statute miles)

• Each satellite is on one of six orbital planes, inclined with respect to the equatorial plane by 55 degrees

• Configuration ensures that at least four satellites will be above the horizon anywhere on Earth simultaneously

Control Segment

• Includes three components▫Master Control Station:

Located at Schriever Air Force Base in Colorado

▫Monitoring Stations: Located in Hawaii, Kwajalein, Ascension Island,

Diego Garcia, and Shriever Air Force Base ▫Ground Control Stations:

Referred to as Ground Antenna, since they are unmanned installations operated remotely

User Segment

•Includes an antenna and receiver that can provide positioning, velocity, and precise timing measurements to a user located on the ground, in the air, or over water. 

How GPS Works

• A GPS receiver's job is to locate four or more of these satellites, figure out the distance to each, and use this information to deduce its own location. This operation is based on a simple mathematical principle called trilateration.

Trilateration

•The basis of GPS is "trilateration" from satellites. •To "trilaterate," a GPS receiver measures distance

using the travel time of radio signals. •To measure travel time, GPS needs very accurate

timing which it achieves with some tricks

Trilateration

•Along with distance, you need to know exactly where the satellites are in space. High orbits and careful monitoring are the secret.

•Finally you must correct for any delays the signal experiences as it travels through the atmosphere.

Trilateration

Knowing that we're 12,600 miles from a particular satellite narrows down all the possible locations we could be in the whole universe to the surface of a sphere that is centered on this satellite and has a radius of 12,600 miles.

12,600 miles We’re somewhere on the surface ofthis Sphere

12,600 miles

16,000 miles

The intersection of two spheresis a circle

A second measurement narrows our position down to the intersection of two spheres - an imaginary circle

Trilateration

Intersection ofthree spheresis only two points

16,000 miles

12,600 miles

14,000 miles

A third measurement narrows our possible position to just two points

TrilaterationTrilaterationTrilateration

Trilateration

• We can discard one point

• One point will be a ridiculous answer▫out in space

▫or moving at high speed

• But we do need a 4th measurement for a technical reason we will talk about later

In practice 3 measurements are enough

TrilaterationTrilateration

Fourth measurement will decide between two points

Fourth measurement willonly go through one of thetwo points

Trilateration

Terms to Specify Position on Globe

•Latitude: degrees north and south of equator.•Longitude: degrees east and west of

Greenwich, England.•Meridian = line of constant longitude.•Parallel = line of constant latitude•Great circle = circle inscribed on surface by

a plane passing through earth’s center.• Universal Transverse Mercator = allows

precise measurements in meters to within 1 meter

Latitude

Axis of rotation

Equator

LatitudeParallels

LongitudeAxis of rotation

Equator

Longitude [Prime Meridian]

Longitude

Meridian

Global Coordinate System

All meridians aregreat circle arcs.

All parallels, exceptfor the equator, are small circles.

Everyday Uses for GPS

•Land and Sea Navigation•Hunting•Boating and Fishing•Vehicle Tracking and Communication

(OnStar)•Mapping•Most new vehicles are being equipped

with GPS navigation units.

Commercial Uses of GPS

•Military tracking•Space Travel•Air Traffic Control•Robot and Machine Guidance•Missile Guidance•Surveying and Mapping•Many other Engineering Uses

GPS 72 Receiver Basics

•Navigation Screens

•Longitude, Latitude and UTM coordinates

•Waypoints•Tracks•Routes

Navigation Screens

• Information Page – shows signal strength and satellites• Map Page – displays waypoints and tracks• Pointer Page – compass that displays navigational direction and

speed of travel• Highway Page – displays upcoming waypoints & travel

direction• Active Route Page – displays active route and waypoints on

route

Interface Keys

• Quit – stops current display

• On/Off• GoTo – link between

waypoints• In – zoom in• Out – zoom out• Page – page selection• Menu – menu options for

each page• Enter – select or enter key• Rocker Key – moves

selection up, down, left and right

Refer to Garmin Users Guide

Time to Practice

Geocaching

•Geocaching is an entertaining adventure game for gps users. Participating in a cache hunt is a good way to take advantage of the wonderful features and capability of a gps unit. The basic idea is to have individuals and organizations set up caches all over the world and share the locations of these caches on the internet. GPS users can then use the location coordinates to find the caches. Once found, a cache may provide the visitor with a wide variety of rewards. All the visitor is asked to do is if they get something they should try to leave something for the cache.

•As of today, there are 104899 active caches in 207 countries.

Geocaching Websites

•Geocaching: The Official Global GPS Cache Hunt Site - http://www.geocaching.com/

•Buxley’s Geocaching Waypoint - http://www.brillig.com/geocaching/

•Letterboxing North America - http://www.letterboxing.org/

•GIS Lounge - http://gislounge.com/features/aa012301.shtml

What are the rules in Geocaching?•Geocaching is a relatively new

phenomenon. Therefore, the rules are very simple:

•1. Take something from the cache •2. Leave something in the cache •3. Write about it in the logbook •Where you place a cache is up to you.

What does a Geocache Look Like?

•Geocaches are generally in some sort of water proof container like a rubber maid box, five gallon pail, or ammunition box. The words “this is a geocache” may often appear on the top with the longitude and latitude coordinates.•Caches generally do not contain anything of significant value, just small items of interest or collectables. •Sometimes the name of the cache will give a clue to its contents.

Geocaches around the U.S.

How to Find Geocache Coordinates•The sites listed above have geocaching

coordinates for all over the U.S.. However, geocaching.com is considered the official website for finding and logging caches. You can explore caches by zip code, state, or country. The site will provide cache names, coordinates and dates the cache was placed and last found. http://www.geocaching.com/

Using Maps with GPS

•Navigating areas that you don’t know can sometimes be dangerous. Since GPS units will only direct you in a straight line, it is necessary to know the terrain you will be traveling. This can be done with topographic maps as well as aerial photographs.

What is a Topographic Map

•A map that shows the contours of the earths surface with contour lines.

•Contours make it possible to measure the height of mountains, depths of the ocean bottom, and steepness of slopes.

Types of Topographic Maps

•[7.5-minute maps | 15-minute maps | 1:100,000-scale series | County map series]

•[1:250,000-scale series | State map series | National park map series]

•[Shaded-relief maps | Topographic-bathymetric maps | Antarctic maps]

Most Commonly Used

•Most USGS map series divide the United States into quadrangles bounded by two lines of latitude and two lines of longitude. For example, a 7.5-minute map shows an area that spans 7.5 minutes of latitude and 7.5 minutes of longitude, and it is usually named after the most prominent feature in the quadrangle.

Free Topographic Map Sites

Some of these sites also provide satellite aerial photographs

GIS Mapping

•GIS is a technological field that incorporates geographical features with data in order to map, analyze, and assess real-world problems.  The key word to this technology is Geography – this means that some portion of the data is spatial, in other words, data that is in some way referenced to locations on the earth.

Topographic Maps & Aerial Photos

Topographic Maps & Aerial Photos

Topographic Maps & Aerial Photos

Topographic Maps & Aerial Photos

Topographic Maps & Aerial Photos