CODEWITHSUNDEEP
quaternions
Luca
Luca

Reputation: 71

Quantity of motion from quaternions

I made some recordings from a head tracker which provides the 4 values of the quaternions, which are saved in a csv (each row is a set of quaternion plus a timestamp). I need to calculate for the whole recording how much the head moved. This is needed for an experiment where I would like to see whether under a condition the head moved more or less compared to another condition.

What is the best way to get a single quantity for each recording? I have some proposals but I do not know how much appropriate they are:

PROPOSAL 1) I calculate the cumulative sum of the absolute value of the derivatives for each quaternion value, then I sum the 4 sums together to get a single value

PROPOSAL 2) I calculate the cumulative sum of the absolute value of the derivatives of the norm

Upvotes: 0

Views: 125

Answers (1)

James Tursa
James Tursa

Reputation: 2636

Sounds like you just want a rough estimate of total angular movement as a single value. One way is to assume minimum rotation angle between quaternion samples and then just add up those angles. E.g., suppose two consecutive quaternion samples are q1 and q2. Then calculate the quaternion multiply q = q1 * inv(q2) and your delta-angle for that step is 2*acos(abs(qw)). Do this for each step and add up all the delta angles.

Upvotes: 1

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