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  • Helical Angles to Roll, Pitch and Heading

    Hello all,

    I`m using VICON Nexus 1.8.4 to measure subjects with the full body plug in and I want to compare the data with a accelero-, magento- and gyrometer combination. Basically, I've attached the sensor between LPSI and RPSI and want to compare the Roll, Pitch and Heading of the sensor with the same variables of the Pelvis segment measured with VICON. As I am not very knowledgable about rotational angles and conversions of such, I'm having difficulties understanding the output from VICON (Global-Pelvis; Helical Angles) and converting it into the desired Roll, Pitch and Yaw.

    Can anyone guide me to the right direction or explain what I need to do?

    Thanks in advance.

    Hans

  • #2
    Re: Helical Angles to Roll, Pitch and Heading

    Hans,

    There have been a few postings on Biomch-L about this, I did a quick search on "helical angle conversion" and found:



    Neither is exactly what you need, but there are some useful references to help you get familiar with the math. You could also try searching Biomch-L with different key words.

    Basically, what you need to do is compute a rotation matrix out of your helical angles, and then decompose that rotation matrix into three successive pitch, yaw, roll rotations. For the last step, you can find some Matlab code in the Kinemat toolbox:


    Helical angles are the product of rotation angle and a normalized axis of rotation. Angle is therefore the norm of the three helical angles, and the axis is the helical angle "vector" divided by its norm. Having axis and angle, you can convert to a rotation matrix, see, for example,
    http://www.euclideanspace.com/maths/...trix/index.htm. THen convert rotation matrix to pitch-yaw-roll Euler angles as I mentioned above.

    Don't blindly use any formulas you find, you need to carefully think how pitch-yaw-roll correspond to X, Y, and Z rotations and in which sequence.

    There is some old Fortran code by Herman Woltring that can do all of these conversions, so if you are comfortable with Fortran you may be able to use that. http://isbweb.org/software/movanal/prp.fortran


    Ton van den Bogert

    Comment


    • #3
      Re: Helical Angles to Roll, Pitch and Heading

      Hans,

      There have been a few postings on Biomch-L about this, I did a quick search on "helical angle conversion" and found:



      Neither is exactly what you need, but there are some useful references to help you get familiar with the math. You could also try searching Biomch-L with different key words.

      Basically, what you need to do is compute a rotation matrix out of your helical angles, and then decompose that rotation matrix into three successive pitch, yaw, roll rotations. For the last step, you can find some Matlab code in the Kinemat toolbox:


      Helical angles are the product of rotation angle and a normalized axis of rotation. Angle is therefore the norm of the three helical angles, and the axis is the helical angle "vector" divided by its norm. Having axis and angle, you can convert to a rotation matrix, see, for example,
      http://www.euclideanspace.com/maths/...trix/index.htm. THen convert rotation matrix to pitch-yaw-roll Euler angles as I mentioned above.

      Don't blindly use any formulas you find, you need to carefully think how pitch-yaw-roll correspond to X, Y, and Z rotations and in which sequence.

      There is some old Fortran code by Herman Woltring that can do all of these conversions, so if you are comfortable with Fortran you may be able to use that. http://isbweb.org/software/movanal/prp.fortran


      Ton van den Bogert

      Comment

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