Davis Protocol. Problem with local coordinate system

[Andrea Gargamelli]

Dear everyone,
I'm a student of Master Degree Engineering and I'm doing a thesis about implementation of Davis Protocol on the OpenSim and I will do a reseach about physical dificulties on the elderly.

I'm editing a model "walk_subject10", but a I don't understand how I can change (origin and versor direction) the local coordinate system of the bones. The Davis Protocol uses the origin of local referement system on the center of mass of each element, instead, the "walk_subject10" uses another system.

Thanks for the help
Andrea Gargamelli

[Stefan Lambrecht]

Hi Andrea

I assume that you are using the Davis marker protocol to collect data in studies related to ... in an elderly population. There is a tool available from Padua, it is called MOtoNMS (it helps you organise your datacollection files and processing for use in OpenSim0.
I am not related to this group but think that this tool is worth looking into, especially if you are starting. However, you do not need this to use OpenSim.
If you want to change the marker protocol then you can do this via the GUI or directly in the XML file. You can use the raw marker data as input to OpenSim and process the kinematics using InverseKinematics. Depending on your laboratory settings you may need to perform a transform (in OpenSim Y-axis is pointing upwards).

[Andrea Gargamelli]

Hi Stefan,
Thanks you for your answer.
I have already used OpenSim for doing a forward squat jump simulation and comparation than results obtained from Matlab algorithm implementation. Now I would create a model with the same coordinate system of Davis Markers Protocol exploiting and modify the models provided on the Simtk.com (I don't no if it's possibile).
I read something on Simtk user guide about the possibility to work directly to XLM (I think that it's the better way to modify the existing model).

Andrea