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Hello,

Has anyone had trouble visualizing ground reaction forces from .mot files? I can view it using preview motion data, but when I try to load it I get this error message:

'Could not associate motion to current model'.

I'm doing work with upper extremity falls and am just trying to visualize the grf during the landing. However, I also get this same error message when using an example model (Gait2354_simbody) with its associated example .mot file subject01_walk1_grf.mot.

What am I doing wrong here. Do I need to change something in the model file?

Thanks,

Brent

Brent,

To associate a motion with a model, OpenSim tries to see if there is coordinate data in the file, because otherwise the association is only based on time which you can do by synchronizing motions in the GUI rather than loading and associating the motion with the model.

Does that explain?
-Ayman

Ayman,

I should apologize for starting this thread in the discussion rather than the users forum, my mistake.

What you are saying makes sense. However, even if the .mot file has coordinate data I cannot get the motion to load in the model. It is also not very clear to me on how to synchronize two motions. The synch option never seems to be available (its there and I can see it, but I can't click on it).

Brent

Brent,

I'm not sure how you create your motion files, but it's possible there's something with the headers/tabs/spaces that confuses the parser. Excel and Matlab sometimes introduce these problems. If you can submit the model and motion in a bug report I can take a look and let you know.

On synchronizing motions, you have to have two models (one of them could be just data-previewing) and select both motions (from the two models) simultaneously (with shift-click), then you can sync. the motions.

Hope this helps,
-Ayman

Hi Ayman and all,
I have a similar problem.
I have run inverse kinematics, and now I need inverse dynamics.
When I preview the grf.mot file, all I see is the yellow-red-green axis system.
1. How can I visualize the forces?
2. the marker motion data .trc file and the grf.mot files have different data rates, is that OK?
3. If I try to load motion, grf.mot file, I get "could not associate motion to current model." Should I be trying to load the grf.mot?
Thanks,
John

Hi John,

1. to Visualize the forces you have two options: either preview motion data (which makes some assumptions about file headers to define forces) or associate motion data (then you'll be allowed to define what to visualize and frames, shapes, etc.) which is more flexible but requires user interaction.
2. The data rates being different is not an issue (when you position the motion slider at a specific time, it samples each motion at the desired time).
3. If the grf file has no coordinates then the behavior is explained by earlier messages in this thread. you can use the "associate motion data" feature however ad load externalLoads file to visualize the forces.

Hope this helps and please let me know if you continue to have questions.

Best regards,
-Ayman

Thanks Ayman,
I understand what you are saying, but I am having trouble doing it.
I would like to view ground reaction forces (file transformed_comfortable3_grf.mot too large to Attach)
synchronized with IK results: according to load specification: I am trying to follow directions here:
http://simtk-confluence.stanford.edu:95 ... h+a+Motion

I see my running model and a ground force arrow, but the arrow is not moving.

Thanks for any help.
John

Here are the other files: Here are screen shots of what I am doing. The green GRF arrow appears, but it is not moving.
John

The grf file in my previous post has a problem. Here is the original:

Hi John,

There are issues with the format of the latest file, for example:
#columns = 19 in header while there're only 6 entries per row
there're empty and trailing tabs on each line

Trying to plot the data from the file using the Plotter shows how it's interpreted by OpenSim. Plotting the trajectory of px,py,pz shows random patterns that explain why the forces don't show up properly.

Please consult the page below for documentation regarding the file layout, in the meantime please file a bug report and attach the file so that we report better diagnostic error messages.

http://simtk-confluence.stanford.edu:80 ... t%29+Files

Best regards
-Ayman