Using your compass
Magnetic sensors in your phone enable a wide range of useful navigation options beyond simply determining what compass direction you are facing. They do however require some care in how they are used to get the best out of them, or in some cases to avoid getting dangerously inaccurate readings! This page gives a list of important considerations for using a phone compass, followed by trouble shooting ideas for common problems. For tips on how to use your compass for navigation see the general user guide.
Things to know.
1. Not all Phones have a magnetic sensor!
Without a magnetic field sensor your phone won’t be able to tell what direction you are facing and you won’t have access to any magnetic compass features. All Apple devices include a magnetic sensor but there are a large number of Android devices that do not, particularly cheaper models. If you are planning on doing any outdoor activity then it is well worth investing in a phone that has a compass sensor. To determine this, check the manufacturers specifications for your phone, or one you are considering, and look for a sensor called ‘magnetic field’ or ‘magnetometer’ or ‘e-compass’. These specifications will be on the manufacturers website or through third party sites such as www.gsmarena.com. It is important not to confuse this with the phones orientation sensors (gyroscope, gravity). These sensors detect some aspects of phone orientation but not compass direction – although they can optionally be used to smooth out the magnetic compass signal.
2. It is essential to calibrate the sensor *every* time you use it
If you want the detailed physics of how a phone compass works then you’ll have to look this up yourself, but the end effect is that the magnetic sensors used in current phones need to be rotated around so that the sensor can align itself properly with magnetic north, and to filter out other interfering magnetic signals.
Fortunately this calibration is easy to do – your phone in fact will automatically carry out this calibration as you move around naturally without you needing to do anything. However, there are ways to enhance this process and improve your chances of getting a reliable measurement, particularly when you first start using the compass sensor after the phone has been off or stationary. There are plenty of guides around, and different methods that all work, but this video shows two functional options. Note that you don’t need to be running a separate dedicated compass app, you can do this whenever you start using the NZTopo50 app and need a compass bearing.
3. Avoid interference
Other magnetic field sources can interfere with proper compass operation. Common ones to watch out for include phone cases that have magnetic clasps in them, and other portable magnetic devices such as traditional fixed magnet compasses, electric fields generated by electric engines, or localised geological features which have their own magnetic properties. Some of these can (and should) be avoided. Others may be compensated for by good calibration. In some cases magnetic interference can’t be avoided and you may get a biased reading.
Problem solving
1. The NZTopo50 app shows ‘Compass accuracy low’
This may occur if you phone thinks that calibration is needed (see above) or that there may be a large interfering magnetic field present. It may also occur because you have selected to use movement bearing instead of the magnetic sensor for compass direction – this is an option for those scenarios where movement direction is more reliable or useful, such as off road driving. This mode is also used by default if your device doesn’t have a magnetic sensor. Because this measurement depends on movement, the ‘accuracy low’ indicator will show when you are moving slowly or are stationary, and the direction indication will likely be variable or inaccurate. Look for ‘Use GPS Course’ in the list of Options and turn it off to use the magnetic sensor as your compass.
2. My compass points in the wrong direction
See discussion on calibration above. If a persistent bias exists for no obvious reason then restarting your phone may help fix some issues.
3. I don’t see the compass display at all
Check that ‘Show Compass Overlay’ is on from the list of Options.
4. The app says that my phone doesn’t have a compass sensor
Some phones don’t. By default the app will use movement in your GPS location to calculate a bearing. In this case you will only be able to determine your direction when you are moving and it may have limited accuracy at walking or slower speeds. Your phone may also report that your compass is inoperable if there is a persistent interfering magnetic field, such as from a case with a magnetic clasp.
5. Can I align the map to the direction I am facing.
Yes. Toggle the ‘follow’ button until you see the crosshairs and compass needle indicator. The map will align itself with the direction that you are pointing your phone (e.g. if you are pointing you phone east, then the map will be aligned with east towards the top – or if you aim your phone at a geographical feature such as a mountain peak, then the map will be aligned so that the mountain peak is directly above (ie further up the screen than) your current location (which is at the center of the screen).