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negative values for resultant acceleration?

I was wondering how, when calculating resultant acceleration which I assume to be sqrt(axax+ayay+az*az) a negative value is achieved. Presumably this has something to do with the way in which 'gravitational acceleration' was dealt with? I would be grateful for more information about this process.

Thank you

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2 Answers
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Accepted answer

Hi Thilo

The resultant acceleration data were calculated within the IMUStep proprietary software which accounted for the resting acceleration associated with gravity. Negative acceleration output from IMUStep indicates that the measured resultant acceleration was less than resting values.

(Resultant = sqrt(x2 + y2 + z2) - gravity).

Thank you

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Accepted answer

Hi Daniel,

thanks so much for answering my question about calculation of resultant acceleration. I think my email has possibly not reached you hence some further comments/questions below.

So I assume this approach was chosen since you were not able to estimate orientation of the IMU and subtract gravitational acceleration from the true vertical acceleration?

I guess the challenge with that approach is that the same value of zero can be the result of the accelerometer being 'immobile' when the resultant acceleration is equating to 1g (positive vertical acceleration of 1g) and then subtracting 1g

OR it could be the foot accelerating downwards with 2g (i.e. the resultant acceleration being 1g with vertical acceleration being -1g) and then subtracting 1g of the value.

Thilo

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