Accelerometer wiki page erroneous axes ?

rixed at rixed at
Wed Apr 8 15:06:36 CEST 2009

-[ Wed, Apr 08, 2009 at 04:32:41PM +0400, Paul Fertser ]----
> I beg to disagree. If you are talking about acceleration of the sensor
> itself then you'll see that: 1. it's not actually accelerating if you
> attach a reference frame to the Earth (the freerunner is laying
> still).  2. The gravitational force applied to the sensor is directed
> to the center of the Earth,

OK untill here.

> so the reported "acceleration" should be positive too.

The reported acceleration is positive, this is a fact (cat /dev/input/event3).
The question is : is a positive acceleration accelerating downward or upward ?

The wiki tells that a positive acceleration is downward (Z axe pointing down).
This is not true, in my opinion.

When standing still, the accelerometer must report an acceleration directed in the
_oposite_ direction the the gravitational force. As it is reporting a positive
acceleration, then the Z axe goes up.

And I believe the other axes are inverted as well (which, as suggested by Michael,
is easily provable by turning the FR around so that each axes points down).

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