Accelerometer wiki page erroneous axes ?

rixed at rixed at
Wed Apr 8 10:48:38 CEST 2009

Please have a look at the "accelerometer data retrieval" wiki page at .

It is said that "the Z axis is pointing from the display downwards to to the
back of the openmoko". In my opinion this is false and all other axes
my be inverted as well.

The confusion seams to originates from the Z value you read from the
accelerometer which is positive when the phone lies horizontally. But the fact
that the gravitation vector G points downward means that the acceleration
measured by the sensor is actually upward : gravitationnal force is equivalent
to an acceleration in the other direction (remember the elevator analogy :
beeing pulled down toward the ground by gravity is equivalent to standing in an
elevator that continuously accelerate _upward_ in the absence of gravity).

So, the fact that when idle the accelerometers report a positive Z value
implies that the Z axe is actually upward.

Agree ?

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