GPS Part II: How GPS Tracks Your Runtastic Activities

Thanks for joining us for part two of this helpful, informative set of posts about all things GPS!  If you happened to miss the first post and would like to start at square one, please check out GPS Part I:  GPS, Runtastic & You for a quick, clear intro to the topic.

Running with GPS
Running with GPS tracking is the basis of the Runtastic app – since most smartphones have GPS technology built into them, they can be turned into a GPS receiver at the touch of a button or use with GPS apps.  It’s the GPS receiver’s job to work out where it is in the world, this is achieved by working out how far away the satellite is from the receiver.  The satellite sends out a radio signal containing the time, the receiver then gets this signal and works out how long it took for the signal to arrive – it then uses the time difference to work out the distance.  Once the receiver knows how far away the satellite is an imaginary sphere is drawn around the satellite, with the satellite being the center.  We’re approximately 32,000 km away from the satellites, but we could be 32,000 km away in any direction from the satellite we’ve locked onto.

Once one satellite has been locked onto and a sphere is drawn, three more satellites are locked onto and three more spheres are drawn.  So we have four imaginary spheres and one real one – Earth.  The point where all five spheres overlap is where the receiver is (in the case of Runtastic app usage, receiver = you and your smartphone)!  This technique is called Trilateration.

Of course, the GPS receiver could have the wrong time, which would cause issues.  However, fear not – GPS satellites contain atomic clocks and therefore always have the correct time.  The GPS receiver will use the signal from the fourth satellite for correction.  With this information, it then completes an equation to work out the correct time and precisely locate you.  If the time from the satellites was wrong, then the GPS system could become inaccurate by about 11 km a day!

Now, once your phone has your location, this data needs to go somewhere.  This is when GPRS (General Packet Radio Service) or 3G as most people call it, kicks in.  The location information is sent via 3G to its intended destination (normally a server) to be processed.  For example, if you use GPS with Google Maps the data goes to Google servers.  When you’re running with GPS with Runtastic, your data comes to our servers. When your data arrives, our servers begin whirring away and tracking you on the map as you run!  This is how people can see you during your activity in real-time with LIVE Tracking, if you opt to use this feature.  When you finish your activity, all your data is on your phone ready for analysis.  However Runtastic won’t use up all your data allowance since the amount of data sent it tiny, it only needs to load your section of the map – so a run around the block uses virtually no data!

But GPS doesn’t need 3G (or WiFi) to work! Phones use data to get a location fix quicker (assisted GPS) and to download your area of the map. So if you were to use an app that had the entire globe – or at least a section you were covering – downloaded and saved, you could switch off 3G and still see your location as the GPS receiver would still be receiving location information.

Once the location is worked out, your GPS receiver (smartphone) will constantly receive the radio signals which enables a new location to be calculated.  The new location is sent to the servers, data is processed on the fly and your movement is tracked when running!  This of course, all happens very quickly – it’s an incredible system and feat of technology – which allows you to track and analyze your Runtastic activities with ease.  You lace up those shoes & let us take care of the rest!

Summary & Tips
So, now you know!  When you start your next activity and track yourself with GPS, you’ll have a better understanding of just how you are being located – satellites, signals and data!

Some key GPS points to remember include:

• • • 24 GPS satellites exist
    • Satellites send out radio waves
    • GPS receivers needs three or more signals
    • Where the imaginary spheres overlap is your location
    • Data is sent via 3G/phone masts to servers
    • Servers process data
    • Tall buildings, forestry, cloud, water & crowds can interfere

What’s more?  The GPS system is constantly being maintained and updated.  In fact, the current satellites being launched are known as GPS III and will allow quicker and more accurate tracking.

Great news for us and great news for you!  Get out there today and move a little (or a lot!)…  The Runtastic team wishes you “Happy Tracking!”

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