The applications that run on Android and iOS phones, referred to as Apps, continue to impress me. Soon after setting up my phone, I took my dog for a run. After we stopped, the fitness App popped up and displayed how many calories I burned during my run. This was quite surprising to me, I didn’t have to configure anything, the phone just knew that I was running and I had stopped. I followed the Apps instructions and placed my finger below the camera, and the heart rate sensor began to calculate, 120 beats per minute. We continued walking up the hill and as curiosity got the better of me and I opened up the App again. The App changed my runner icon to a hiker and displayed an elevation graph along with how many steps I had taken.
I know what you’re thinking right now, “what does this have to do with indoor navigation?”
The answer to that question is everything.
The phone is able to know that I’m running because it is loaded with sensors. A barometer determines my elevation based on changes in barometric pressure and the pedometer counts my steps. The accelerometer and gyrometer detect how quickly I’m moving and in what direction, this information is used to determine if I’m riding a bike or running, as they are both about the same speed, but the motions are very different. The GPS is able to determine my location by communicating with satellites orbiting the Earth. This allows me to use GPS for driving directions, however once you cross the threshold into a building, GPS becomes largely useless. GPS satellites don’t work indoors because they don’t have a line of sight to the sky. Walls and ceilings prevent GPS, but now there is an ingenious way to use the building itself as the tool for tracking you inside. Modern buildings all have a unique magnetic signature produced by the Earth’s magnetic field which interacts with steel and other magnetic material found in structures of buildings. The magnetometer, which powers the compass, can detect this magnetic signature.
This is made possible by recording the unique magnetic signature of the building. If you are looking for a technical explanation, you can read the white paper, however, I have a far better example you may relate to. In the movie The Dark Knight,
Gotham city is mapped using millions of cell phones allowing Batman to navigate indoors in complete darkness. The cell phones could detect the sound waves reflecting from each object nearby, allowing the cell phones to create a map of the area. This is exactly how a bat navigates caves in complete darkness and thus the reason why this technology was used in the movie. While the sonar technology used in the film remains the stuff of Hollywood fiction (so far), similar results can be obtained with magnetic imaging. The magnetic sensor is able to detect the weak magnetic field created by the iron within the steel structure of the building. Unlike in the film, magnetic imaging isn’t able to determine where people or furniture are located as they are not magnetic This allows the magnetic signature of a room to remain unaltered during renovations. Magnetic imaging can tell you where you are,more importantly, it needs to know where you are going, while you are going there. This is where the other sensors that I mentioned previously with the fitness App, come into use. The pedometer can be used to determine the pace at which an individual is walking so that the popup for the next turn happens just a few steps before when the turn is to take place. Unlike car navigation where each vehicle must remain in their lane, large indoor spaces do not have ‘lanes’ so the gyroscope is used to determine when an individual changes direction in an open space.Changes in elevation, such as when entering an elevator or using an escalator, can be detected by the barometer. Upon exiting the elevator, the barometer will detect no further changes in elevation and this allows the App to determine the exact floor by connecting to the WiFi. These sensors intelligently work in the background providing directions without requiring any input from the user. One of the most amazing things about this technology is that it doesn’t require an expensive infrastructure of beacons or other devices, since it utilizes the Earth’s magnetic fields that can be measured on a standard cell phone – it is a great leap forward in our ability to provide the same type of navigational experience indoors as we’ve become used to outdoors.