Knowing where your thumb is

Accuracy of GPS depends on several factors. In general better accuracy, down to cm precision, requires expensive reception systems. Credit: GIS Stack Exchange

Location based services are now commonplace and we have started to use them seamlessly, no longer realising they are there. 
GPS is what provides the magic: the Global Positioning System leverages on the time it takes to signals to travel from a number of satellites (at least three, better if more) orbiting around the Earth to reach your receiver (the smartphone, the car navigator, ...) and by triangulation calculates your position on planet Earth. Interestingly, the calculation has to take into account relativistic lengthening of time resulting from the high rotational speed of the satellites in their orbit.

How much accurate is the GPS positioning? Very much indeed. It can pin you down to the centimetre. However, to reach such a precision you would need to carry a quite sophisticated, and cumbersome, antenna. In practice the resolution is within a few metres and in bad coverage situation may be within a few tens of metres. 

This kind of accuracy is good enough for navigation purposes but it fails if you need to pinpoint an object you are looking at by head movements, as it happens in virtual reality goggles. A tiny movement of your body and head should lead to a change in what the virtual reality system is showing you. 

This is now becoming possible thanks to a system developed by researchers at the University of Texas in Austin. It provides centimetre accuracy to the GPS signal making it possible to deliver services where high localisation accuracy is fundamental.  
In addition to virtual reality games you can imagine its application in drones navigation letting them deliver a parcel right to your door; the accuracy is such that it can pinpoint a location as small as a nickel.

The feat has been accomplished by looking at the phase of the received signals. This is also what happens in a number of insects to pinpoint the direction of the sound. Their ears (sort of) are too close to pick up the sound delay resulting from the additional travel distance from one ear to the next but such a distance is sufficient to detect a difference in the phase of the signal.

It is a kind of accuracy that can tell you where your thumb is ....

Author - Roberto Saracco

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