Trace an eight in the air with your mobile to calibrate the compass
As with the compasses that you surely used during your childhood, the sensor that mobile phones usually include detects the earth’s magnetic fields to indicate which cardinal point the top of the mobile is pointing to. Thanks to this, you will not only know where the sunrise is or how to orient yourself in the open field, you will also have key help in applications such as Google Maps: knowing in which direction you should start the route.
The magnetometer included in smartphones is a tiny sensor that can be altered by the small electromagnetic fields generated by the mobile’s own circuits, it is also affected by other nearby devices or metal surfaces where you can rest the smartphone (or surround it). For this reason, it is usual for this sensor to not clearly detect the north magnetic pole; so you will need a calibration that will help you separate the earth’s magnetic field from the rest of magnetic interference. That’s where the eight trick comes in.
Perhaps a warning has appeared on Google Maps that the compass of your mobile needs a calibration and that for this you need to draw a kind of figure eight in the air. And that’s exactly what you have to do:
- Hold the phone well in your hand, it is easy that in one of the turns it can fall out.
- Turn your wrist to the right while slightly moving your hand in that direction.
- Make a turn in the air in the opposite direction, to the left.
- Join both movements in a loop and repeat them for about twenty seconds or until Google Maps (or any other application) tells you that the compass is already calibrated.
Once you have calibrated the compass the point that represents you on the map will point in the right direction. In this way you can go in the direction you want without having to move for the GPS to detect the direction.
In general, you should not need a compass calibration, it will all depend on several factors:
- You are in an environment with magnetic interference. Inside the car it is usually quite common, for example.
- If you haven’t calibrated in a while.
- It highly depends on the quality of the phone. The more category your mobile has, the better sensors it will have incorporated; so they will suffer less interference.
Why is it necessary to calibrate the mobile compass?
We have already explained how the phone sensor works roughly: the magnetometer detects the earth’s magnetic field and transfers the information to the system. Due to the interference that this sensor suffers, it is common for it to become out of adjustment; creating distortions in the magnetic plane that the system has saved: These distortions prevent the phone from accurately positioning itself in space. With one last aspect to keep in mind: the compass does not work alone, since it relies on the accelerometers and the gyroscope (if the mobile includes it, something that is already very common) to position the phone in space.
In order for your Google Maps to show you with the blue arrow pointing in the right direction (and without moving), the application takes data from:
- the magnetometer. The compass itself obtains data from the different magnetic fields that surround the mobile to create a three-dimensional low-precision plane (X, Y and Z axes).
- accelerometers. These sensors tell the phone if it is moving in the X and Y axes. That is, it allows the system to know the orientation of the mobile (vertical or horizontal) as well as the movements that affect it.
- the gyroscope. This sensor positions the phone precisely in the three axes of space: X, Y and Z.
When the compass cannot determine what the Earth’s magnetic field is because it suffers from interference, moving the mobile in a figure eight allows the system to compare the readings obtained in the three axes of space (X, Y and Z) with those it has stored in the magnetic plane. This allows you rule out erroneous positions restoring reliability to the compass. The mobile not only uses the readings of the magnetometer, it also contrasts them with the accelerometers and the gyroscope. This increases the reliability of the orientation.
The trick of the eight is much more useful than it seems and it really works: with this calibration the system can determine the orientation of the phone. And, given that for said calibration position readings must be made in the three axes of spaceto “zero the compass” there is no choice but to move the mobile in the air.
In general, it is enough that you do the figure eight trick only when apps like Google Maps ask you to do so. Though you can also do this move right before you open the maps app, for instance. This ensures that the arrow of your position points correctly to where you are looking.
More information | Stack Exchange, Quora
