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Hello,

I am trying to restructure the gait2354.osim Coordinate and Joint structure. I am having trouble initializing the integrator using the edited model. The example code is available at https://github.com/vinaym815/OpenSimExa ... 54.cpp#L13.

In this example I wished to remove the z axis translation of the ground_pelvis custom joint. First, I changed the Z axis translation function to a constant one and then removed the coordinate using the CoordinateSet.remove(). I am able to initialize system; however, the program crashes when I try to initialize the manger. The edited model still have pelvis_tz coordinate in the XML file and removing it solves the issue. Any idea how to remove this redundant coordinate programatically.

Thank You

Hello Vinay,

Can you explain why you want to remove a coordinate? In general coordinate definitions are part of the joint type (underlying computational system, allocates state variables based on joint type) so coordinates can't be removed, however they can be locked to a specific value if you want to fix them. Please explain what you're trying to do so we can suggest solutions.

Best regards,
-Ayman

Hi Ayman,

aymanh wrote: ↑

Mon Feb 10, 2020 10:35 am

Can you explain why you want to remove a coordinate?

I wanted to synthesize Sit to Stand motion. Since the joints undergo states with substantial hip and knee flexion angles, I wanted to simplify the Full Upper and Lower Body Model https://simtk.org/projects/model-high-flex. The simplification would involve restriction of motion to two dimensional space as well as the removal of some muscles. To achieve this I wanted to edit some exiting joint definitions.

aymanh wrote: ↑

Mon Feb 10, 2020 10:35 am

They (the coordinates) can be locked to a specific value if you want to fix them.

I thought of doing that but editing the joints seemed like a cleaner solution and most probably computationally efficient as numerous forward simulations will be run by the optimization algorithm.

Thank you
Vinay

Update: I discovered editing the XML to be much simpler than expected (primarily because none of muscle wrap points were conditioned on the coordinates). However, I have a follow-up question. Why the coordinates are part of joint definitions? If they were independent:
1) We would not require OpenSim::CoordinateCouplerConstraint(),
2) Implementing symmetry within the models would have been easier.
3) Muscle Conditional Path points are functions of coordinates and occur as part of muscles, independent of joints anyways.