Re: Android Sensor Coordinates
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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Bailey goes on to say that
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