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  • What is GPS?

    GPS (Global Positioning System) is the world's first satellite navigation system. It was developed by the U.S. Government's Department of Defense, who gave GPS its official name: the NAVSTAR system (Navigation Satellite Timing and Ranging).

    GPS consists of 3 key elements:

    • Satellites in space
    • Monitoring Stations on Earth
    • And last but not least, you and your GPS receiver.
    The satellites

    GPS has 24 satellites that circle Earth in six orbital paths, sending out radio signals from their position in high orbit, 12,600 miles/ 20,300 kilometres above our heads. Being so high, each satellite's signal covers a large area of the earth's surface and their orbits have been 'choreographed' so that your GPS receiver back on Earth is always getting signals from at least 4 satellites, the number you need to pinpoint your location.

    The monitoring stations

    There are 5 monitoring stations: the master station in Colorado Springs, USA and four unmanned stations. One on Hawaii, the other three in remote locations as close to the equator as possible: Ascension Island in the Mid Atlantic; Kwajalein in the Pacific and Diego Garcia Atoll in the Indian Ocean.

    The 4 unmanned stations receive constant data from the satellites and forward it to the master control station, which 'corrects' the data and then sends corrected data back up to the GPS satellites.

    GPS signals

    Your GPS receiver picks up signals from GPS satellites to work out your location. The last, important step in the process is of course you making use of that information.

    Each satellite transmits low power radio signals on different frequencies for different users. The signals travel by so-called 'line of sight'. This means they pass through clouds, glass and plastic, but not usually through solid objects, such as buildings.

  • The history of GPS

    How it all began

    In 1957 the former USSR launched the first man-made satellite: Sputnik 1. Scientists quickly realised first that by using the Doppler Effect one could work out a satellite's orbit. Then that by turning it round, you can use satellites to work out the position of a receiver on earth.

    The foundations of the modern GPS were laid during the early 1960's by the US military. The Navy, Air Force and Army each came up with their own designs and ideas, and eventually in 1973 a design that incorporated elements from each was approved by the US government. This was to become NAVSTAR.

    The first satellite for the new NAVSTAR GPS was launched in 1974 and from 1978 to 1985 another 11 were launched for testing purposes. The full constellation of 24, that today allows your navigation system to enjoy worldwide GPS coverage, was completed in 1993.

    GPS for everyone

    Initially GPS was only intended for military use. But then tragedy struck. On 1st September 1983, Korean Airlines flight KAL007 from Anchorage to Seoul strayed off course into USSR airspace and was shot down by a soviet Su-15 fighter jet. All 269 passengers and crew were killed.

    Two weeks later, US President Reagan proposed GPS be made available for civilian use to avoid navigational error ever again leading to such a catastrophe. While by no means the only reason, the Korean Airlines disaster was certainly a major catalyst toward civilian access to GPS.

    Selective Availability (SA)

    Having spent some $12 billion to develop the most accurate navigation system in the world, the US government then built a function called Selective Availability (SA) into NAVSTAR that would limit its accuracy for civilian users to ensure no enemy or terrorist group could use GPS to make accurate weapons.

    It worked by introducing deliberate errors into the data broadcast by each satellite. Military users could access the fully accurate system by decrypting a secured second frequency that was broadcast simultaneously.

    Then during the Gulf War the US military needed many more GPS receivers than it had. It solved the problem by using civilian GPS receivers. But to increase the accuracy of these devices, the SA function had to be temporarily disabled. Then in 2000, US President Clinton announced that SA would be disabled completely. Because US government 'threat assessments' concluded that removing SA would have minimal impact on national security. Though in the same speech he said the US would still be able to 'selectively deny' GPS signals on a regional basis when national security was threatened.

  • Who uses GPS?

    GPS has evolved well beyond its original objectives to become a can't-do-without resource for all sorts of people and all walks of life. From transport and service industries to ocean-racing sailors. From stress-free holiday motoring to the easiest, most fuel-efficient way to get from A to B.

    And as satellite positioning information becomes more and more sophisticated, so new uses are constantly being found for GPS. Not only for transport (vehicle location, route searching, speed control, etc), but also less obvious applications such as sea and mountain search and rescue.

    Equally important is the ease of access to such information. It's one thing to be able to use GPS if you're part of an expensive military or scientific team. But nowadays anyone can walk into a shop, buy a SatNav and be instantly plugged into the most sophisticated navigation system in history.

    Doubtless some of the recent developments in civilian SatNav use, such as locating an on-route restaurant, might seem rather frivolous to the original satellite navigation pioneers. But no one can deny that recent private applications of GPS are making the lives of all sorts of people more productive, safer and less stressful.

  • How does GPS work?

    GPS (Global Positioning System) has 24 artificial satellites that orbit the Earth at a distance of 12,600 miles/ 20,300 kilometres, transmitting radio signals. The pattern of their orbit is 'choreographed' so that a GPS receiver anywhere on the earth's surface is always 'visible' (and therefore receiving signals) from at least 4 satellites.

    From these 4 satellite readings your GPS can work out your location through 'Trilateration'. It is essentially the same idea as triangulation, but without using angles.

    Explaining trilateration in 3-D space is a little tricky, so let's start with simple 2-D trilateration.

    2-D Trilateration

    Imagine you're completely lost. You wake up in a strange hotel room one morning with no idea at all where you are. You go downstairs and ask the hotel receptionist, "Where am I?"

    "I can't say" he says, "but I will tell you you're 593 miles/ 955 kilometres from Copenhagen."

    You now know you're somewhere on a circle round Copenhagen with a radius of 593 miles/ 955 kilometres.

    You stroll into town and, stopping off for a coffee, ask the waitress where you are. "375 miles/ 604 kilometres from Paris" she says and walks away.

    You then notice the table napkins. As luck would have it, they are perfect detailed maps of Europe! You take one, pull out your handy compass-and-ruler accessory set and draw two circles. So:

    You now know you must be at one of the two points where the circles intersect. The only two points both 593 miles/ 955 kilometres from Copenhagen and 375 miles/ 604 kilometres from Paris.

    Back on the street an old man calls you over. He tells you that you are 317 miles/ 510 kilometres from Prague. You whip out your napkin and compass and draw another circle.

    You now know exactly where you are: Frankfurt!

    3-D Trilateration

    3-D trilateration is basically the same idea as 2-D trilateration. You just need to imagine the 2-D example above, but with 3 spheres instead of 3 circles.

    Let's say you know you're 10 miles/ kilometres from satellite A. This means you could be anywhere on the surface of a huge, imaginary sphere with a 10 mile/ kilometre radius.

    But if you also know you're 15 miles/ kilometres from satellite B, you can overlap the first sphere with this second sphere with a 15 mile/ kilometre radius.

    The two spheres will intersect in a perfect 2-D circle.

    And if you also know you're 8 miles/ kilometres from a third satellite, when you make this third sphere, you will find it intersects with the circle at two points (just like the two-circle diagram in the 2-D example).

    But you also have a 4th sphere handy: the Earth itself. Only one of the two intersecting points you've just identified will actually be on the Earth's surface. So, assuming that you're not floating around somewhere in space, you now know exactly where you are.

    However, GPS receivers normally use at least 4 satellites to improve accuracy.

  • Alternative satellite systems


    GLONASS (Global Orbiting Navigation Satellite System) is the Russian satellite system, which became fully operational in December 1995. Like GPS, GLONASS also uses 24 satellites and though slightly more accurate than GPS, its big drawback was that the satellites only lasted about 3 years.

    With a Russian economic crisis in the late 90's, the satellites were not always replaced, so that the system gradually lost its effectiveness. By 2000, only 8 of the 24 satellites were still operational. However, for the last few years, Russia has been working hard on a GLONASS comeback and hopes to have the system fully operational again in 2012.


    GPS BLOCK III is the new version of GPS. The biggest improvement on the current GPS system is that GPS III will send out a more powerful signal. It will also follow a different orbit, so countries on higher latitude, such as in Scandinavia, will now get better coverage. Another major advantage is its ability to operate accurately together with GALILEO, the new European satellite system.


    GALILEO is the new satellite system of the European Union. One of the key reasons for the EU to develop its own satellite system was so that it would no longer be dependent on GPS.

    GALILEO will provide greater accuracy and coverage than GPS and is mainly intended for civilian use. It is due to be completed in 2008/9 and the first satellite was launched in December 2005. It will eventually consist of a constellation of 30 satellites orbiting at some 14700 miles/ 23,600 kilometres above Earth.


    Despite the impressive accuracy of GPS and GLONASS, two further systems were launched to make them even more accurate. WAAS (Wide Area Augmentation System) for the American continent and EGNOS (European Geostationary Navigation Overlay System) for the European continent.

    Each consists of three satellites that send out signals to receivers. Measuring stations then calculate if the satellite signal has a discrepancy and sends any correction to two of the three 'geostationary' satellites. These geostationary satellites beam the correction signal back to Earth, where WAAS/EGNOS -enabled GPS receivers apply that correction to their computed GPS position.

    However, the new GPS III and GALILEO systems will not work together with WAAS or EGNOS, as they'll be able to measure and correct their own inaccuracies.

  • Satellite facts

    The satellites travel at 7,000 miles/ 11,250 kilometres per hour, which means they circle the earth once every 12 hours.

    GPS satellites are powered by solar energy. Smart enough. But smarter still is the fact that if their solar energy supply temporarily fails (e.g. because of an eclipse of the Sun), the satellites have back-up batteries on board to keep them running.

    The satellite signals have low power; about 20-50 watts. Compare that with the signals from an FM radio station, which are about 100,000 watts. If you imagine trying to pick up a 20 watt signal from over 12,000 miles/ 19,000 kilometres away, you'll realise why you need a clear view for a GPS signal…

    Like to know more satellite facts?
    • Altitude: 20,200 kilometers
    • Weight: 860 kilograms (in orbit)
    • Size: 5 meters with solar panels extended
    • Orbital Period: 12 hours
    • Orbital Plane: 55 degrees to equatorial plane
    • Planned Lifespan: 7.5 years
    • Current constellation: 24 satellites
  • Advantages of Digital Mapping

    The world is made up of countless millions of roads, from huge motorways to small streets and galis. The mapping of all these routes, as well as all the various street directions and other details that affect them, is carried out by governments and other statutory organisations across the globe. Their maps form the basis of all maps, including the digital maps for your Trakker NAV. These maps were verified and enhanced by TPL Trakker's GIS (Geographical Information System) Department to include more and more areas and provide accurate street and house address data.

    Digital maps can be updated

    Apart from the fact that traditional maps are less convenient and less interactive and therefore less efficient than digital maps, one of the main reasons traditional paper maps are being superseded by digital maps, is that a paper map cannot be updated.

    On average, 5% of roads are altered in some way every year. So with a paper map that's only 2 years old, you have close to a 1 in 10 chance of being wrongly directed with each reading you take!

    In fact, given the time-lag between getting the data for the maps and then drawing them up, getting them typeset, printed, distributed and so on; a new paper map is already out of date before the ink on it is dry.

    The on-going challenge to digital mapmakers is to reduce the delay between a change occurring in the road system and its appearing in the map in your navigation system.

    Trakker NAV has employed a large GIS team to meet this challenge and make your digital map as up-to-date and accurate as possible.

    More than just directions..

    The huge range of information digital maps can provide (with traffic signs, prohibited manoeuvres, vehicle restrictions, house number ranges, points of interest, tourist information, and much more) is just another example of how much more user-friendly they are than traditional maps.

    So whereas even the best traditional maps simply show you where you are, and perhaps indicate road signage etc. (as it was at the time of printing), digital maps take the information you get to another level altogether.

  • How does digital mapping work?

    Keeping digital maps up to date

    There are 3 main ways to collect the data to develop and update digital maps:

    • Fieldwork. Data collectors driving the road networks of the world, recording changes and discrepancies.
    • Analysis of aerial and satellite imagery.
    • Customer feedback.

    At Trakker NAV, for example, any map feedback from customers via the website are reported to our GIS department, who look into every single case and , where appropriate, actually send surveyors out to physically check the locations.

    Digital mapping is a time-consuming and logistically challenging process. So a company like TPL Trakker is constantly developing new technologies and practices to increase the speed and comprehensiveness with which their maps are updated.

  • The Trakker NAV Device

    Now that you know more or less how GPS works, you may be wondering what exactly your Trakker NAV device does with all this GPS information it receives.

    Inside your Trakker NAV

    Your Trakker NAV may not be big, but it's very clever. Pulling together all the data available from GPS and converting it into something that can navigate across cities with amazing accuracy.

    More than just getting you from point A to B

    By making smart use of any new technological advances, your Trakker NAV doesn't just bring you to where you want to be. It makes getting there ever more efficient, relaxed and fun.