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Getting to Grips with a Global Positioning System (GPS)

Learn the basics of the Global Positioning System (GPS), including its history, limitations, and how to choose and use a handheld GPS device. This guide provides informative resources and a user guide for beginners.

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Getting to Grips with a Global Positioning System (GPS)

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  1. Getting to Grips with a Global Positioning System (GPS) Tom Burke

  2. Content • Introduction • Background • GPS’s & the GPS Systems explained • Limitations of a GPS handheld device • Making your choice – a buying guide • Basic user guide • Useful links - resources

  3. Introduction Aims • By the end you should feel you have enough knowledge (or know where to look for further research) to be in a position to choose & use the basics a handheld GPS system should you wish. Objective • To give an overview of the Global Positioning Satellite System & how a Handheld Global Positioning System works. • To provide you with an informative guide to the functions, features & user interfaces (UI’s) of the various hardware & software options. • To provide you with a basic user guide for handheld GPS’s.

  4. Background • The global positioning satellite system was developed by the US Military during the cold war in order to increase the accuracy of intercontinental ballistic missiles. Global Positioning Satellite System (GPSS): • In order to limit civilian use the they degraded the signal to reduce accuracy. • In 1995 the US GPS system became fully operational. • In May 2000 selective availability was removed to give an average accuracy of 15m. • In 2007 the Russian GLONASS system (another GPSS) was scheduled to become fully operational. • As of March 2008, the system is not fully available, however it is maintained and remains partially operational with 16 operational satellites.

  5. Background cont. • Aside from the US & Russian systems, two other systems are in the ‘pipe line’. • The European one which is called GALILEO and was planned for completion in 2010. • The other system is being built by China and is called Beidou. It’s completion was planned for 2008 when it would be providing an “open” level of service with 10m accuracy. • However it would appear that both systems are still in their infancy with a little way to go before completion. • With Galileo, the second Satellite, of the planned thirty was only launched in April, they are now predicting an completion date of 2013 with the third satellite scheduled for launch in 2010. • It would appear that the Chinese system currently only has 4 Satellites (as at Feb 2007) and will continue to be used for testing.

  6. Background cont. • These systems are designed to increase the accuracy of GPS’s; typically by a factor of around 5 which equates to a position fix to 3m. Satellite Based Augmentation Systems (SBAS) • They work using geostationary* satellites and ground based relay stations to improve the signal quality from the GPSS. • Because the system is based on fixed positions, coverage availability is limited. • You also require a compatible device which will show in the specification as WAAS (US) or EGNOS (European) compatible. *geostationary – in a fixed position above a point on the earth

  7. How the GPS System Works • GPSS uses a system of satellites (the US system uses 24) 11,000 miles above us in space. • These are circling along a number of axis’s around the globe at 1,000 miles per hour sending radio signals back to earth. • Usually at least 6 satellites are visible at any one time.

  8. How the GPS System Works cont. • A GPS Receiver can log on to 12-14 satellites simultaneously. • A GPS needs to log on to at least 4 satellites and, by sharing a combination of distance, time and position information between the satellites, gives the user a fix of latitude, longitude and elevation. • This is known as a 3D fix.

  9. Points to Note • A handheld GPS is an excellent ADDITION to your traditional navigation methods. • It will never replace the map & compass • It will give you a position fix even in hill fog, blizzard or ‘white out’. • The service a GPS uses is completely free bar the cost of replacing batteries.

  10. Limitations of a GPS • Make & Model The make and model will govern what your GPS will be capable of. Obviously you are restricted by what is available but ensure you choose a make and model that suits your current and future needs. • Standard Features & Design The features & design will affect its performance & flexibility. Memory size, colour screen, electronic compass, barometer & altimeter can enhance the users experience. However the compass, barometer and altimeter are only useful if regularly calibrated & calibrated correctly. Things like battery type (power) and the antenna type used will affect signal strength. • Additional Features Memory expansion slots for saving data Included or additionally bought mapping software PC link-up for upload & download of data and loading maps or new firmware

  11. Limitations cont. • User Ability You will only get out of your GPS what you put in. To be able to use your GPS to its fullest potential you will need to spend time with the manual / or a guide book to learn how it works. Alternatively you can book yourself on a dedicated training course. • Terrain in your surroundings • Location / Position (in the world) • Battery / Power • Antenna type • Reception Signal & strength The whole system relies on a good line of sight to the satellites: the stronger the signal, the more accurate the position fix will be. Reception is how good the connection to the Satellites are; the more satellites you can gain reception from them, again the more accurate your readings. The available reception will affect the GPS’s signal strength; the following can affect or block the GPS’s reception & signal strength: NB. Reception is unaffected by bad weather

  12. Limitations cont. • Reception cont. • False Signals • Atmospheric conditions • Multipath errors Terrain in your surroundings Reception can be affected by Tree cover, Gullies, buildings, your body and other objects. Location / Position (in the world) In some locations the satellite coverage (path routing) is better that others. If your in a poor area you will not get as good / will struggle to get a sufficient signal. This could result in a 2D fix (which does not include elevation) or a False signal. Battery / Power In order to obtain a strong signal handshake your GPS sends a signal to the Satellite. The strength of the signals will determine which satellites you log onto and this in turn affects the GPS’s accuracy. When there is sufficient power the signal will run at the designed maximum but as the power is lost the GPS is unable to maintain max power which then affects how many satellites it can reach and logs onto.

  13. Limitations cont. • Reception cont. • Antenna type There are two types of GPS aerial – quadrifilar helix (right) and patch (left). A quadrifilar helix aerial is more sensitive and will generally get a signal where a patch will struggle. • False Signals If a false signal is being received, the speed or location could be inaccurate. This can be caused by poor satellite geometry. If all the satellites within your GPS’s line of site are clustered closely together or are situated in a line away from the antenna, it is more difficult to calculate positions. • Atmospheric conditions This can affect the speed of the GPS signals to the satellite and cause your handset to do strange things. This could be as a result of Solar activity in the Ionosphere. • Multipath errors A multipath error is where the GPS receives two signals from the same satellite. This can be caused by a satellite signal being bounced of rocks or similar in your location.

  14. Buying Guide

  15. 1.Zoom In/Zoom Out Whilst viewing the map screen, press to zoom the map view in and out. Look at scale on screen. On any other page use these keys to scroll up and down a list or to move a slider bar. 4.Find/Options Press and release to cycle through the screen pages This button can also be used to ‘quit’ a process when working within a page. Press and hold in to toggle the electronic compass on and off (certain models only). 2.Find/Options Press and hold to show the waypoint find menu. Press and release to show the options menu for a page. 5. Power/Backlight Press and hold in to switch on and off. When GPS is on, press and release to switch on and adjust backlighting, view the date and time, satellite and battery status. Move slider bar on screen to adjust brightness. 3. Thumb Stick (a four way scrolling device and Enter button) The GPS is designed to be used in the left hand with the thumb stick being operated with the thumb. Press down and release to select highlighted options or data or to confirm on screen messages. Push up/down/left/right to move through lists, highlight areas, buttons or icons or to move the map panning arrow on the map screen.

  16. My Ideal GPS profile Budget: Minimum: £________ Maximum: £_______ • I will not buy a GPS without these features • These features are nice to have if the price is right but not essential • I will not pay extra for these features as I will never use them

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