polonskyg

I'm trying to figure out what the meaning of the output from gravity sensors means in Android.

I understand is the gravity applied in X, Y and Z, what I don't understand is the difference with accelerometer sensor.

I know gravity is a fuse sensor which uses gyroscope as well and others...but getting for example a value of 29.4 (9.8 * 3) in the gravity[0] sensor means that there is a force of 3G applied in the X axle?

So it would similar to use acceleration = SQRT(X^2 + Y^2 + Z^2) but more precise?

Thanks in advance! Guillermo.

Snedd

I don't think it uses the gyroscope. In the stock gingerbread source it looks like the gravity sensor is just a low pass filter of the accelerometer data. If the device is at rest the gravity and accelerometer sensors should give identical data.

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polonskyg

Can you please specify in which file have you seen this? I tried searching for it in here: GrepCode: android.hardware.Sensor (.java) - Class - Source Code View and other files there, but didn't find it.

Thanks! Guillermo.

Snedd

I have the source checked out of android.googlesource.com. Its actually implemented in 'C', not java:


frameworks/base/services/sensorservice/GravitySensor.h
frameworks/base/services/sensorservice/GravitySensor.cpp

and

frameworks/base/services/sensorservice/SecondOrderLowPassFilter.h
frameworks/base/services/sensorservice/SecondOrderLowPassFilter.cpp

This looks like an online version :

services/sensorservice/GravitySensor.cpp - frameworks-base in rowboat - Gitorious

there's probably others if you search for those filenames on google, but I recommend getting your own copy of the source tree if you're into this sort of stuff, there's instructions here:

Downloading the Source Tree | Android Open Source

it takes a while but its worth it.

Last edited by Snedd; February 9th, 2012 at 01:27 AM.