Get Accelero, Gyro and Magneto in same time Android

Question

I'm working on Sensor fusion with Accelerometer, Gyroscope and Magnetic Field on Android. Thanks to SensorsManager I can be noticed for each new value of theses sensors.

In reality and this is the case for my Nexus 5 (I'm not sure for others Android devices), acceleration, rotation rate and magnetic field are sampled in same time. We can verify it using event.timestamp.

On others systems (like iOS, xSens...), Sensor SDK provides a notification with these 3 vectors in same time.

Of course, when I receive an acceleration(t), I can write some lines of codes with arrays to wait rotationRate(t) and magneticField(t). But if there is a way to have an access directly to these 3 vectors together it could be very interesting to know!

An other question relative to sensors data: Is there advices from Android team to device constructors to provide data in chronological order ?

Thank you,

Thibaud

Answer 1

Short answer, no, Android doesn't provide a way to get all the sensor readings as it reads them.

Furthermore, the behavior that you've observed with SensorManager, namely that readings from different sensors happen to have the same timestamp suggesting that they were read together - should not be relied upon. There isn't documentation that guarantees this behavior (also, this is likely a quirk of your testing and update configuration), so relying upon it could come to bite you in some future update (and trying to take advantage of this is likely much more difficult to get right or fast than the approach I outline below).

Generally, unless all results are generated by the same sensor, it is impossible to get them all "at the same time". Furthermore, just about all the sensors are noisy so you'd already need to do some smoothing if you read them as fast as possible.

So, what you could do is sample them pretty quickly, then at specific intervals, report the latest sample from all sensors (or some smoothed value that accounts for the delta between sample time and report time). This is a trivial amount of extra code, especially if you're already smoothing noisy sensor data.

Answer 2

There is a workaround for this particular problem. When multiple registered listeners are present in an activty at the same time, timestamp for those event may be misleading. But you can multiple fragment objects into the said activity which have different context's. Then listen to every sensor in these fragments. With this approach the sensor reading timestamps become reliable.

Or listen in parallel threads if you know about concurrency...