Pokemon GO-bal Positioning System

Earlier this July, my childhood dream finally came true.  Over the series’ 20 year history, I’ve played more than 30 Pokemon video games, and with each new release I’ve wanted to become a gym leader and to catch ‘em all – a feat I accomplished, once, back in the first game.   Now, as a 28-year old working on a Ph.D., I can finally achieve my dream with the help of Niantic’s latest augmented reality game, Pokemon GO.

 IMG_2016-07-10-13445138 I can find a Pidgey (the Pigeon Pokemon) on a city sidewalk thanks to GPS telling Pokemon GO where I am.  Finding a Goldeen (the Goldfish Pokemon) on the same city street would not make sense.

In Pokemon GO, as I wander around my city, my phone periodically vibrates indicating that I’ve found a Pokemon.  I quickly look at my phone and tap on the Pokemon to enter a battle with it.  The game knows where I am thanks to GPS, the Global Positioning System, and uses that information to show me location-appropriate Pokemon, such as Water-type Pokemon close to rivers and Fire-type Pokemon in deserts.

Of course, GPS predates Pokemon Go by several decades, and has many far more serious applications.  The idea for the system came about at the dawn of the Space Race, when scientists at the Advanced Physics Laboratory first devised the idea of using satellites to calculate location.  In the 1960s, US nuclear-missile carrying submarines used a set of six satellites to calculate their location once an hour.  In the mid-70s, the Department of Defense embraced the idea of constantly being able to locate oneself, so they launched their first GPS satellite in 1978. They achieved their goal of continuous GPS services in 1993.  

The Global Positioning System is a group (known as a constellation) of 32 satellites located 12,500 miles above the surface of the Earth.  This puts them above the home of the Sky High Pokemon Rayquaza and the International Space Station, but below the satellites used for TV and communication and the space-dwelling DNA Pokemon Deoxys.  The United States’ 32 GPS satellite constellation is just one of many.  The Russian’s have their own global system (GLONASS), and many phones can take advantage of the combined 56 satellites of GPS and GLONASS to improve position accuracy and coverage.  The European Space Agency and China National Space Administration are also currently developing their own global systems.  India is developing it’s own regional system, so that it can maintain positioning services independently of foreign governments that may deny India access during war.  Japan is also developing its own satellite constellation  that broadcasts at the same wavelengths of other GPS signals to improve accuracy within Japan.  

GPS24goldenSML

As satellites orbit the Earth, they send signals to my phone.  At any one time, my phone can receive signals from at least six satellites.  (Source:  Wikipedia)

Each of these satellite navigation systems works on the same principle.  A GPS satellite beams a message announcing where it is located and precisely what time the satellite sent the message.  In my phone, a tiny antenna picks up signals from the GPS satellites.  That information is all my phone needs in order to know where it’s located.  The phone has a rough idea of the time it received the signal, and the satellite’s message says when it was sent, so the phone can calculate the signal’s travel time and the distance it had to cross to get from the satellite to me.

Satellite Explanation

A 2D simplification of how three satellites allows me to know where I am.  Adding a fourth satellite also allows me to calculate my elevation.

My phone is constantly receiving these signals and calculating distances from multiple satellites, because a signal from just one satellite isn’t enough to know where I am. If we simplify down to two dimensions on the Earth’s surface, knowing my distance from one satellite tells me I can be anywhere on a circle.  Even two signals from two different satellites isn’t enough to specify exactly where I am as I could be at the two points where the circles intersect.  On a two-dimensional plane, three satellites with three different signals is the minimum number of satellites I need to know my position.  If I care about my position in three dimensions because I’m using the Beak Pokemon Fearow to Fly, I need an additional signal from a fourth satellite in order to pinpoint my latitude, longitude, and elevation.  When my phone “sees” more than four satellites, I can get more and more precise with my location and deal with signal interferences.  

Many things interfere with my phone’s ability to get the signals from GPS satellites, and therefore my ability to catch Pokemon.  Materials that don’t interfere with the signals sent from GPS satellites include cloth, glass, and cloud cover (so the Weather Pokemon Castform is safe).  But buildings often interfere with GPS signals, and being inside concrete buildings or in the urban canyons of skyscrapers and city streets renders GPS signals frequently unusable.  Other interference sources include the ionosphere, a layer of charged particles 50-200 miles up that can reflect GPS signals back into space; space weather; and other radio signals.  And a note to any aspiring Water-type trainers: don’t use Dive, as being underwater significantly weakens the GPS signal.

Pokemon GO is the latest application of the Global Positioning System, but it’s not the first augmented reality application of GPS.  Most applications of GPS do more than just calculating my location; they also use that information to augment my reality.  Google Maps augments my reality by using GPS to display maps with step-by-step directions to the closest Gym. In some places, emergency response dispatchers for 911 can augment Officer Jenny’s reality by providing my cell phone’s GPS coordinates to help her find me (and cell phone providers are working to make it more wide spread).  Fishermen use GPS-augmented reality to keep track of spots where there are plenty of fish (perhaps including the Fish Pokemon Magikarp) so that they can go back for more later.  GPS has been augmenting our reality since 1993, and Pokemon GO is just the latest use.  But it is the first to let me get out there and finally become the very best, like no one ever was.

 

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One thought on “Pokemon GO-bal Positioning System

  1. Pingback: Augmented Reality: How it Works and Affects Our Lives – RCScientica

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