Finding Joint Angle from Motion Capture

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Mary
Mary 2012-12-12
评论： Suranjita Ganguly 2020-6-23
Hi!
I'm working right now with data from a motion capture device, essentially picking up data for three markers placed on the head neck and shoulder in an x y z plane.
My difficulty trying to develop a code to calculate the joint angles between these three markers. I am able to animate the three coordinates to play as an animation, but I'm more interested in the calculation of the angles between these points changing over time.
Any ideas on how to go about this?
Thanks

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Roger Stafford
Roger Stafford 2012-12-12
At any time, let H = [x,y,z], N = [x,y,z], S = [x,y,z] be coordinate vectors of the head, neck, and shoulder markers at that time. Then the three respective inner angles within the triangle HNS then are:
h = atan2(norm(cross(N-H,S-H)),dot(N-H,S-H));
n = atan2(norm(cross(S-N,H-N)),dot(S-N,H-N));
s = atan2(norm(cross(H-S,N-S)),dot(H-S,N-S));
(The sum of these should always be pi to within round-off accuracy.)
Roger Stafford
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Mousumi Nag
Mousumi Nag 2017-1-24
Can I get back the S,N,H from the angle .In other words, How can I get the vector points where angle is given
Suranjita Ganguly
Suranjita Ganguly 2020-6-23
The sum of the angles should be Pi (approx), because the three angles are forming a triangle, and sum of all internal angles in a triangle is 180 degrees i.e. pi

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