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  • Hi,

    Is there any good ways to get acceleration sensor data without gravity? Like it would use magnetometer to get the orientation and then remove gravity based on it? Some ready made examples.
    I would like to calculate 3-4 seconds the speed the watch has and if possible, also a location/orientation.

  • location will be GPS lat/lon ? It will take you at least 20 seconds to power on the GPS and get a fix and that is assuming you have downloaded AGPS data - otherwise expect 12 minutes for the first fix.

  • I guess you not think of GPS but double integration of acceleration.
    Be warned, that is very difficult - basically an ill posed problem for several reasons!

    Main thing is that every sensor is noisy. Integration amplifies this noise, so you will have wrong speed. This will change your location all the time without bounds, even if in reality you are standing still. So after double integration you will have very big error after very short amount of time.
    The only way you have a chance to get reasonable location from accelerometer is to make use of some other constraints.

    That could be the Magnetometer if you operate quite close to a strong magnet, but no way to count on earth magnetic field (lots of noise from all kind of metal and fields in the environment)

    Depending on what you want to do, you might think of instead make use of the gravity, since this is something that can anker you. But of course only if you can discriminate gravity and acc through some other constraints or system model (not magnetometer unfortunately).

    All this is not specific to bangle but true even for much more expensive sensors.


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