In the past decade, transportation both at the consumer and business level has undergone rapid transformations resulting in improved productivity and customer experience. The key to that has been the ability to track movement in real time. Real time tracking is ubiquitous, but for the transport managers and technically inclined it is fascinating to go beyond the surface of visual maps to understand how GPS and other location tracking methods work.
The Global Positioning System (GPS) developed by US, is a satellite-based navigation system made up of 27 satellites. Smartphones and GPS devices which have GPS receiver built in to them, are the two most popular devices for location tracking. If the vehicle carries a Smartphone or GPS device, to identify its 2-D position (latitude and longitude), the GPS receiver in a device or phone connects with at least 3 satellites. If it locks with 4 or more satellites in view, the receiver can determine its 3-D position (latitude, longitude and altitude).
As illustrated in the above image, the GPS receiver identifies its distance to each of the satellite to deduce its location through mathematical technique trilateration – a complex version of triangulation. Generally, a GPS receiver tracks 8 or more satellites and connects with 3 or 4 satellites to determine its location. As the vehicle moves, the distance between the GPS receiver and the satellite varies, enabling the receiver to compute its location instantly. As per official US Gov report, the GPS receivers in Smartphones/GPS devices can typically locate within 4.9 meter accuracy depending on various terrestrial and atmospheric conditions.
Cell Tower Triangulation
Cell tower triangulation is another technique widely used to identify the location of the phone/device. A cell phone signal may be picked up by three or more cell towers enabling the triangulation to work. So when a triangulation happens – with the point of overlap of three signals, it is possible to estimate the location of the cell phone based on its distance from the three towers. The cell towers broadcast their location and by knowing the distance of the phone from each towers, the co-ordinates of the cell phone is calculated. Average accuracy of cell towers could vary between 500m – 1500m. In urban areas where towers are in every nook and corner, it is possible to deduce the location of phone/device with greater accuracy.
It is fair to wonder what Wi-Fi has got to do with identifying your co-ordinates. Companies such as Google and Apple have been using this method to identify your location. So how does this work? Phones have a background location service which constantly seeks for Wi-Fi access points and sends Wi-Fi addresses (bssid) along with its location identified through GPS or cell tower triangulation to their respective servers and stored in their database.
The fact that there are more Wi-Fi hotspots than trees in a city enables Google or Apple to identify your location by merely knowing the strength of Wi-Fi signals on your phone. This data is available for app developers through APIs which any developer can leverage to locate phones using Wi-Fi positioning. The accuracy of Wi-Fi in dense city can vary between 10 – 25m and in sub-urban areas with less access points 20 – 100m.