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Re: Android Sensor Coordinates

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On 3/31/2011 5:03 PM, Lawrence D'Oliveiro wrote:
> The diagram of the linear sensor coordinate system here
> <http://developer.android.com/reference/android/hardware/SensorEvent.html>
> seems to be wrong.
>
> I have a test program running on my HTC Desire (Android 2.2), showing me
> values from the accelerometer. As it lies horizontally, face-up on my desk,
> the Z value is positive (around 9.8, as you would expect). But that diagram
> says that positive Z is up, not down.

Maybe it is showing deviations from free-fall? The accelerometer can
presumably only measure forces that act differently on the case and the
insides.

As a thought experiment only, consider what would happen if the desk
were not there, and the device were in free-fall. It would move towards
the center of the earth, in the negative Z direction. The accelerometer
would briefly report zero.

The device's deviation from free-fall is an acceleration upwards, due to
the upwards force the desk exerts on the device.

Patricia

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Android Sensor Coordinates Lawrence D'Oliveiro <ldo@geek-central.gen.new_zealand> - 2011-04-01 13:03 +1300
  Re: Android Sensor Coordinates Patricia Shanahan <pats@acm.org> - 2011-03-31 17:53 -0700
    Re: Android Sensor Coordinates Lawrence D'Oliveiro <ldo@geek-central.gen.new_zealand> - 2011-04-01 15:44 +1300
  Re: Android Sensor Coordinates Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2011-03-31 18:20 -0700
    Re: Android Sensor Coordinates BGB <cr88192@hotmail.com> - 2011-04-01 11:02 -0700
      Re: Android Sensor Coordinates Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2011-04-01 17:51 -0700
        Re: Android Sensor Coordinates Lew <noone@lewscanon.com> - 2011-04-01 21:23 -0400

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