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How GPS * Works * G lobal P ositioning S ystem How GPS Works The Global Positioning System (GPS) consists of 24 Earth-orbiting satellites. These satellites allow any person who owns a GPS receiver to determine his or her precise longitude, latitude and altitude anywhere on the planet

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how gps works
How GPS Works
  • The Global Positioning System (GPS) consists of 24 Earth-orbiting satellites. These satellites allow any person who owns a GPS receiver to determine his or her precise longitude, latitude and altitude anywhere on the planet
triangulation continued
Triangulation (continued)

If you know you are 625 miles from Boise, you could be anywhere on this circle.

triangulation continued6
Triangulation (continued)

If you know you are 625 miles from Boise and 690 miles from Minneapolis, then you know you must be at one of two points.

triangulation continued7
Triangulation (continued)

With three known points, you can determine that your exact location is somewhere near Denver, Colorado!

measuring distance
Measuring Distance
  • GPS satellites send out radio signals that your GPS receiver can detect.
measuring time
Measuring Time
  • Measuring the time would be easy if you knew exactly what time the signal left the satellite and exactly what time it arrived at your receiver, and solving this problem is key to the Global Positioning System.
measuring time continued
Measuring Time (continued)
  • The only way to implement a system like this would require a level of accuracy only found in atomic clocks.
measuring time continued17
Measuring Time (continued)
  • The Global Positioning System has a very effective solution to this problem -- a GPS receiver contains no atomic clock at all. It has a normal quartz clock.
finding the satellites
Finding the Satellites
  • The other crucial component of GPS calculations is the knowledge of where the satellites are.
cool gps facts
Cool GPS Facts
  • The first GPS satellite was launched in 1978.
  • The current system is composed of second generation GPS satellites, called Block II.
  • The first Block II satellite was launched in 1989.
cool gps facts continued
Cool GPS Facts (continued)
  • The Defense Department declared GPS fully operational in 1995.
  • When the system was first introduced, miscalculations were programmed into GPS transmissions to limit the accuracy of non-military GPS receivers. This operation was cancelled in May 2000.
  • There are 24 GPS satellites in orbit at this moment
cool gps facts continued22
Cool GPS Facts (continued)
  • The 24 satellites cost an estimated $12 billion to build and launch.
  • Each satellite weighs about 1,735 lb (787 kg).
  • The satellites are in orbit about 12,500 mi (20,000 km) above the Earth.
cool gps facts continued23
Cool GPS Facts (continued)
  • A satellite takes 12 hours to orbit the Earth once.
  • The Russians have a system identical to the U.S. system called GLONASS.
what gps can do
What GPS Can Do
  • The Global Positioning System, a collection of 24 Earth-orbiting satellites, has a number of possible applications, spanning across several areas of society.
what gps can do continued
What GPS Can Do (continued)
  • The basic function of a GPS receiver is to figure out its location on Earth.
gps basics
GPS Basics
  • One of the basic characteristics of GPS receivers is that they find your location only when you are outside.
gps basics continued
GPS Basics (continued)
  • The simplest GPS receiver would give you just the coordinates of your location on Earth in latitude, longitude and altitude.
gps basics continued28
GPS Basics (continued)
  • Even low-end receivers have some sort of electronic map stored in memory.
gps in motion
GPS in Motion
  • A standard GPS receiver will not only place you on a map at any particular location, but will also trace your path across a map as you move.
gps in motion continued
GPS in Motion (continued)
  • How far you've traveled (odometer)
  • How long you've been traveling
  • Your current speed (speedometer)
  • Your average speed
  • A "breadcrumb" trail showing you exactly where you have traveled on the map
  • The estimated time of arrival at your destination if you maintained your current speed
gps user input
GPS User Input
  • Most receivers have a certain amount of memory available for you to store your own navigation data.
gps user input continued
GPS User Input (continued)
  • The basic unit of user input is the waypoint.
  • A waypoint is simply the coordinates for a particular location. You can save this in your receiver's memory in two ways:
        • You can tell the receiver to record its coordinates when you are at that location.
        • You can find the location on a map (the internal map or another one) and enter its coordinates as a waypoint.
gps user input continued33
GPS User Input (continued)

Examples of waypoints:

  • Good camp sites
  • Favorite road-side shops
  • Excellent fishing spots
  • Scenic overlooks
  • Where you left your car
gps user input continued34
GPS User Input (continued)
  • You can also combine a series of different waypoints to form a route.
  • One way to use this function is to periodically record waypoints as you make a trip so that you can backtrack, or follow the same route again on another trip.
computer connections
Computer Connections
  • Receivers with route capabilities will let you save a certain number of waypoints to memory so that you can use them again and again.
  • If the receiver has a data port, you can also download your routes to a computer, which has much more storage memory, and then upload them again when you plan to follow those routes.
computer connections continued
Computer Connections (continued)
  • Some recent receivers let you download detailed maps of an area into the GPS, or supply detailed maps with plug-in map cartridges.
  • These maps can give you street-level detail in cities and the receiver may even provide driving directions as you drive!
important features for a hiking gps
Important Features for a Hiking GPS
  • "Map" screen
  • Water proofness
  • Long battery life
  • Built in Maps
  • Route capability
  • Waypoints
  • Multiple Datum capability is pretty standard
important features for a hiking gps continued
Important Features for a Hiking GPS (continued)
  • Fit nicely in your pocket and lightweight
  • Bearing to next waypoint
  • Screen Size
  • 12 channel parallel receiver system
non essential features for a hiking gps
Non-Essential Features for a Hiking GPS
  • A minimum of 8 megs of map memory
  • Rotatable screen
  • UTM readout may be a consideration for some
  • Topo Maps uploaded into your GPS
  • External amplified antenna
see this web site for more info
See This Web Site for More Info

For Hiking GPS Recommendations:

For Auto GPS Recommendations:

w ide a rea a ugmentation s ystem waas
Wide Area Augmentation SystemWAAS

WAAS is based on a network of

approximately 25 ground reference stationsthat covers a very large service area.

  • wide area ground reference stations (WRSs)
  • wide area master station (WMS)
  • ground uplink system (GUS)
  • The WAAS will improve basic GPS accuracy to approximately 7 meters verticallyand horizontally