Android TYPE_LINEAR_ACCELERATION sensor – what does it show?

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Very interesting question!!!!

I’m developing somethig similar to your application. What i found about TYPE_LINEAR_ACCELERATION isn’t happy for me.

1) TYPE_LINEAR_ACCELERATION, TYPE_GRAVITY, ecc are implemented only for Android 2.3 (and up)
So i have Android 2.2 and i can’t test them.

2) TYPE_LINEAR_ACCELERATION isn’t so accurate as it would be, because there are some simple problem when substract the gravity. In fact is a “sensor fusion” that uses accelerometer and orientation to know where is directed the gravity and then subs. it.

Here i found a very usefull answer that explain it:

https://groups.google.com/forum/#!topic/android-developers/GOm9yhTFZaM

TYPE_ACCELEROMETER uses the accelerometer and only the accelerometer.
It returns raw accelerometer events, with minimal or no processing at
all.

TYPE_GYROSCOPE (if present) uses the gyroscope and only the gyroscope.
Like above, it returns raw events (angular speed un rad/s) with no
processing at all (no offset / scale compensation).

TYPE_ORIENTATION is deprecated. It returns the orientation as yaw/
pitch/roll in degres. It’s not very well defined and can only be
relied upon when the device has no “roll”. This sensor uses a
combination of the accelerometer and the magnetometer. Marginally
better results can be obtained using SensorManager’s helpers. This
sensor is heavily “processed”.

TYPE_LINEAR_ACCELERATION, TYPE_GRAVITY, TYPE_ROTATION_VECTOR are
“fused” sensors which return respectively the linear acceleration,
gravity and rotation vector (a quaternion). It is not defined how
these are implemented. On some devices they are implemented in h/w,
on some devices they use the accelerometer + the magnetometer, on
some other devices they use the gyro.

On Nexus S and Xoom, the gyroscope is currently NOT used. They behave
as if there was no gyro available, like on Nexus One or Droid. We are
planing to improve this situation in a future release.

Currently, the only way to take advantage of the gyro is to use
TYPE_GYROSCOPE and integrate the output by hand.

I hope this helps,

Mathias

Anyway, in various place on the web i found no best word about phone sensor and their potential, due to the fact that aren’t accurate…

Some more precision can be reached using Kalman filter, but i have no idea how…

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