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Hello everyone

Setting MuscleDorceDirection plugin on local coordinate system gives you constant values for muscle origin/insertion coordinates which are independent of time. Also it gives you varying muscle force directions with respect to time.

The question is, what are the location and orientation of this local coordinate system themselves??
surely they would be somewhere on the bone but where and by which orientation?

I need to adjust another coordinate system with respect to this one, in my research.

Best,
Yunus.

In the manual of the plugin, it is mentioned that you can choose where to express the positions and forces either in local body frame or in global ground frame.

mitkof6 wrote: ↑

Mon Dec 16, 2019 2:48 am

In the manual of the plugin, it is mentioned that you can choose where to express the positions and forces either in local body frame or in global ground frame.

Hi Dimitar

Let me be more clear, in case of femur, where exactly is the local reference system's origin placed on the bone? How are the x-y-z axes are oriented?

Without knowing that, you can't use the outputs of the plugin.
The outputs are expressed with respect to a local reference system, but Where exactly is this local reference system? And how is it oriented?

Thanks for your help

In the navigation window, you can right click on the body and select the show axis option. This is the local frame of the body. Also, you can check the visible objects and see whether there is any additional transformation that is applied to the nodes of the geometry.

mitkof6 wrote: ↑

Tue Dec 17, 2019 2:08 am

Also, you can check the visible objects and see whether there is any additional transformation that is applied to the nodes of the geometry.

Thanks Dimitar it was quite helpful.

But I need more accuracy. "Show axes" shows you location of local frame graphically while its origin is deep in the bone .
I need to know coordinates of the origin of this frame with respect to something known (like anatomical landmarks ,etc.) so I would be able to set my another local frame in the other app (i.e. Abaqus) and run my simulation using data OpenSim provides me with.

Is there any (anatomical) convention that OpenSim uses to locate these axes on each segment?

Best regards.

You can use the BodyAnalysis, which reports the position and orientation of the body local frames with respect to the ground frame. Otherwise, you can attach markers on the bodies and then get their location in the ground frame (e.g. PointKinematics analysis). If you need to express these points in different reference frames then you have to do it programmatically (e.g., with Python, Matlab or C++).

https://simtk.org/api_docs/opensim/api_ ... Frame.html
https://simtk.org/api_docs/opensim/api_ ... aa78c66f79

mitkof6 wrote: ↑

Wed Dec 18, 2019 2:49 am

You can use the BodyAnalysis, which reports the position and orientation of the body local frames with respect to the ground frame. Otherwise, you can attach markers on the bodies and then get their location in the ground frame (e.g. PointKinematics analysis). If you need to express these points in different reference frames then you have to do it programmatically (e.g., with Python, Matlab or C++).

https://simtk.org/api_docs/opensim/api_ ... Frame.html
https://simtk.org/api_docs/opensim/api_ ... aa78c66f79

Thanks alot