How to retrieve high quality compass orientation (as in Google Maps)?

Question

All of the guides to getting compass orientation in Android I\'ve found have a bug: when you hold the phone in portrait mode and \"look\" above the horizon, the compass arrow tu

Answer 1

1. bug when looking above the horizon.

There is some tricky parts when you work with compass. The compass orientation depends on magnetic fields and phone orientation, so, in order to correct deviation you need to do some matrix operations.

Check this article, it provides a simple example -> https://www.journal.deviantdev.com/android-compass-azimuth-calculating/

Paraphrasing the article: "So if the device is not holding flat (∓45° deviation) you have to use remapCoordinateSystem() in a useful way to get correct results."

2. accuracy.

First of all, accuracy rely on physical components present in the device. Fragmentation is a common problem here. Samsung magnetometers are different from LG's, and Android System is not going to abstract you from this.

On the other hand, devices could rely on different type of sensors: harward or sensor fusion. So you're going to experiment differences between one device and other.

So this is a mess. But it exists some techniques you could apply in order to get accuracy and uniformed data from sensors (not only for compass, probably GPS too).

1. Some people discard the first few seconds of sensor data. Some time is needed in order to calibrate the signal, so the first data retrieved use to have some deviation. The time you need to discard depends on manufacturer again, buy I'd try with 5 seconds or so.

2. Use Interpolators and Extrapolators. Many sensors in android provide you a way to retrieve data each certain milliseconds. But this is the abstraction provided by Android. Harward sensors have its own timing and they update the signal when they they think it is necessary. The rest of the time, when Android ask the sensor for signal data the sensor returns the last value or maybe some kind of operation of the last signal data provided by manufacturer (again).

So, it is interesting to have some abstraction layer (interpolator / extrapolator) which receive the data from Android system each 20, 50, 1000... This layer make some operations in order to have some uniformity, and then communicates the data to your app.

The operation here could be some kind of average between current and last value, accumulated average or maybe another kind of normalization.