simtk.org

Hi,

I would like to know how the Custom Joint relating to Spacial transform in terms of formulation. Is there any paper talking about that?

In Opensim GUI, I found that a coordinate(elv_angle) is trying to Rotate the axis of another coordinate(shoulder_elv).
When I read the attached .osim file, I cannot identify the pattern for the above relationship. Which part of the .osim file stated the relationship between joints/coordinates?

Thanks!!

Regards,
Hilary

A custom joint is a wrapper around Simbody's function based mobilizer:

https://simbody.github.io/simbody-3.6-d ... ml#details
https://simbody.github.io/simbody-3.6-d ... ml#details

Doxygen:

"When you create it, you specify the number of generalized coordinates, and six Function objects which calculate the spatial rotations and translations based on those coordinates."

publication:

https://simtk.org/docman/view.php/47/15 ... 2-p291.pdf

Then you can also create relationships between the general coordinates. This is achieved through constraints (e.g., CoordinateCouplerConstraint).

The SpatialTransform in OpenSim describes how the Child frame moves with respect to the Parent frame of a CustomJoint. It specifies the permissible movement (by user provided functions) on 6 axes (3 rotational and 3 translational TransformAxes) parameterized by generalized coordinates (the joint's coordinates). See: https://simtk-confluence.stanford.edu:8 ... els-Joints