Tracking Marker Coordinates

[Travis Peterson]

Hi all,

I would like to place a marker in my model and run a motion file that I've already described and then output the coordinates of the marker through the motion activity. Is this possible at all? I could convert VICON data, but this seems to be a hassle due to the conversion of real-space data to OpenSim coordinates that are normalized to 1.0

Thanks,
Travis

[Ayman Habib]

Hi Travis,

To record the kinematics of a point on a body you need to run the Analyze "Tool" in OpenSim. Feed it the motion file as input, and add an analysis of type PointKinematics. There (when you specify the analysis) you get a chance to specify the coordinates and the Body that the point (marker) lives on, then when you hit run you get a record of the point trajectory.

Hope this helps,
-Ayman

[Travis Peterson]

I've tried to use this Analyze tool, but when I run the analysis, I get constant values for the kinematics. I input the global coordinates of the marker in question, and used the motion file I have (which is the time history of angle measurements of a flexion-extension activity). Is there something that I'm missing or what might be the cause of the lack of results?

Travis

[Ayman Habib]

Travis,

Please check that you specified a body_name other than ground for the point, and have relative_to_body_name set to ground.

-Ayman

[George Mastorakis]

Hi,

I tried to run on the 2354 model with some markers on. Unfortunately, the distance to the ground is not correct. When standing, the body should be ~ 1.8m, but it shows 1.12m.

Why is this inaccurate?

Thanks

[Aaron Godfrey]

Hi George-
Have you resolved this issue yet?

[George Mastorakis]

Hi Aaron,

Actually I did yes! Would you like the recipe?

George