Scaling/Virtual Markers

[Catherine Scarbrough]

I am trying to scale the pelvis for the subject I am using. I have edited the markers to match the motion capture data we have collected, but have had to add virtual markers as described in the Webinar for Tips and Tricks on Scaling. When I add these virtual markers for scaling, and then try to use them in the scale tool they are not found in the motion capture files we have. This means that I cannot use them for scaling, this data was already collected so I am trying to figure out how I can scale without these markers begin in the actual .trc file. For reference I have attached an image of what it looks like when I try to use these virtual markers I have created.

[Nicos Haralabidis]

Hello Catherine,

These new additional markers for scaling that you added to model, is the hip joint centre one of them as an example? If so, using your motion capture data you need calculate a hip joint centre marker and make sure this new 'calculated' marker appears in your .trc file.

I hope that makes sense!

Kind regards,

Nicos

[Nicos Haralabidis]

I just saw your picture properly. You need to calculate the midASI and midPSI positions from your motion capture data and make sure they appear in your corresponding .trc file.

[Catherine Scarbrough]

The hip joint center is a marker that was already in the motion capture data. The markers that I have added include the Mid ASI, Mid PSI, and Mid HJC. For these would I also have to calculate them using the motion capture data and make sure they also appear in the trc file?

[Nicos Haralabidis]

Hello Catherine,

Yeah, that's right. You will have to calculate them (e.g., midASI etc), for example in MATLAB, and ensure they are then included within your .trc file.

Nicos

[Muhammad Haras]

You can use a Motion analysis toolbox such as Mo2NMS toolbox (MATLAB) to calculate new virtual markers and add these new markers to your .trc markers file. This toolbox reads .c3d files and outputs .trc and .mot files.