Global vs. lokal reference frame

Dear all,
I work with MoCap analysis based on the AMMR.v2.3.4 library and I have some questions about the output of the inverse dynamics considering the reference frame. I get lost in the chart view trying to understand what the reference frame for the joint angles and joint reaction forces is. When looking at the hip, I can see, that the nodes the hip joint is referred to are ThighNode and PelvisNode. Am I right, that the first node gives the reference frame?
Is there a way to see the output values located in the global reference frame or do I have to add something to have to Output in the global reference frame. The topics I found considering the reference frame in this forum were all about ten years old, so I am not sure, whether the information given there is still relevant for me.

Thank you
Best regards

Hi Luisa,

Welcome to the AnyScript forum!

Generally, your understanding is right but the question is framed in a way that I can't give you a simple yes or no answer :slight_smile:
If you are talking specifically about the outputs that you see in SelectedOutputs, then what you are saying is correct. So, the reference frame that appears first in the joint definition gives the reference frame for the joint reaction force.

There is a way to see the joint reaction force in global coordinate system. To do this, you will have to explore to the joint. In there, you can find Constraints.Reaction.RefFrameOutput.M and F. These are expressed in the global reference frame.

And, normally, yes, the information that you find on the forum should be relevant despite the time. But, of course, it depends on the nature of the problem :wink: I would like to point you to a previous post, which is still relevant.

I would also like to point you to the wiki page where you can read more about this.

Best regards,

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