Re: Motions of the left side of the body
The orientation of the subject should not matter if you use a 3D model to calculate joint angles.
This would be easy to verify: invert all horizontal coordinates (X and Z) to simulate a 180 deg rotation about the Y axis, and run the data through your software again. The results should be the same as before.
Ton
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Motions of the left side of the body
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Re: Motions of the left side of the body
So it's as I thought, I can use interchangeably both of them (changing X or Z sign) with the same outcome.
But, I was wondering if this is also right with the subject rotating 180°....in other words if the subject change direction during the acquisition (facing back).
Thanks,
Marco
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Re: Motions of the left side of the body
Marco,
What you did is perfectly fine. I have sometimes used the same trick to avoid having to write separate code to process data from the other side of the body.
Essentially, by inverting the X values, you are looking at your subject through a mirror. So the left side looks like the right side, and you can process the left side data as if it were the right side.
If you invert the Z values instead, you are also looking at your subject through a mirror. This time, the mirror is in the frontal plane, so it switched front and back instead of right and left. But it is still a mirror, so your left side looks like the right side. So it makes perfect sense that this works equally well!
Ton van den Bogert
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Motions of the left side of the body
Dear members,
in order to describe the angular kinematics of the left side of the body (in particular the upper body) which is the best method recommended?
Whereas I use the global coordinate system defined as: Y vertical, pointing upward, X pointing from left to right, Z pointing backward.
I tried to reverse only the sign for the X-coordinate of each raw marker (3D data expressed in the global coordinate system).
Doing so, I can avoid left-handed coordinate systems or changes of definition for each anatomical reference system (using the same matlab program for both sides, instead of define a similar reference system/program for the left side, too).
Repeating the same procedure for the Z-coordinate.... it seams that I get the same result?
Any ideas would be very much appreciated.
Thanks,
MarcoTags: None
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