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Question about 3D motion analysis and Vicon

Discussion in 'Biomechanics, Sports and Foot orthoses' started by kalani, Apr 18, 2010.

  1. kalani

    kalani Welcome New Poster

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    Hello Podiatry Arena :D

    I am a mechanical engineering student who is interested in learning how to use 3D motion analysis (vicon system) to measure ankle in/eversion during running and jumping. I have an appointment to visit a Gait laboratory at a local university but prior to this visit, I wanted to read up as much as possible so I can ask good questions while I am there. With this in mind, I thought I'd run my beginner questions by this forum in hopes there is someone really experienced with 3D motion analysis and Vicon systems.

    From my understanding, the motion analysis of the ankle goes roughly like this:
    - Reflective markers are placed on bony landmarks of the subject (Helen Hayes and modified versions seem to be standard?)
    - Vicon cameras/software are calibrated with static and dynamic tools
    - Subject performs the movement within the volume to be captured by Vicon cameras
    - The raw data captured by Vicon is then processed/filtered in order to be useful 3d coordinate data

    This is where it gets sticky for me:
    - Vicon is used to obtain 3D coordinate information
    - A coordinate system for the ankle joint and the lab must be defined (a standard for this seems to be heavily debated)
    - This allows the data to be oriented and then allows angular displacement and velocity to be calculated

    However, from what I understand, these calculations are not for the weak -- I imagine someone out there has spent time writing a program for this. But I am unaware of any. Is there a depository out there where I can find software that allows you to import Vicon data and then it automatically calculates ankle in/eversion displacement and velocity? Is my thought on this off?

    Hope this makes sense. Much thanks in advance for any comments. :D

    - Kal
  2. andy_ray_Vicon

    andy_ray_Vicon Welcome New Poster

    Dear Kal,

    Please let me introduce myself as the sales and support amanger for Vicon Motion Systems Ltd, Oxford, UK office.

    This type of question can be easily handled by our support team at www.vicon.com/support.

    Please let me know which lab you intend to visit and or use for your studies and I will add you to the support account.

    With respect to your enquiry:

    Vicon does indeed provide 3d reconstructions of the markers placed on the subject, with the psoitions of the markers dictated by which model you inted to use. Vicon supply a plug in called "PluginGait" which is a clinically validated model for the assessment of clincal gait based around the helen hayes markers set.

    The plugin will process the labelled marker data and provide the various kinematics (and kinetics if appropiate) asscoiated with that model.

    There is also a multi segmented foot model availble as a plug in for our sofwtare known as the Oxford foot model.

    The full detail to each of the above models is freely availble from our support site stated above.

    If neither of the two models stated above provide you with the model outputs you wish to analyse then you can:

    1) create your own model using our Bodybuilder software
    2) create a model in a 3rd party applciation such as visual3d, mat lab or labview and export the data from vicon into these packages to process the model outputs you have created within them.

    All the above detail is provided in electronic documenation availble from our website.

    please feel free to come back to me direct on my email or through our support site.

    Kind regards and good luck with your studies.

  3. David Smith

    David Smith Well-Known Member


    At Strathclyde uni they didn't allow us to use processing software and we had spent a lot of time processing raw data ourselves, in Excel for instance. It seems like a lot of time consuming work and mathematical gymnastics and it is but by doing this you get a very good idea of the shortcomings and error areas of 3D data processing. In this way you will appreciate what you are seeing and what you are not seeing in what is shown by commercial software output. You'll be able to see more easily why and how output changes when different assumption are made and when there are various technical considerations to account for.

    Just a thought

    You might try your question on the Biomch-L forum, http://biomch-l.org/ you need free registration first.

    Just a thought

    Cheers Dave Smith

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