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I attached a new body "backpack" to a torso model. I assumed I could define coordinates in any order (e.g. tx then ty ; versus ty then tx). However, when I then associate each coordinate with a DOF in the custom joint, I found that the model would incorrectly move along the x-axis when the value of "ty" changed.
- this is despite specifying that tx should follow (1,0,0), etc.
It turns out that if you define coordinates out of order, the constructor is loading coordinates by index instead of by name.
See attached model files, line 5397
<Coordinate name="backpack_torso_ty">
<!--The value of this coordinate before any value has been set. Rotational coordinate value is in radians and Translational in meters.-->
<default_value>0</default_value>
<!--The speed value of this coordinate before any value has been set. Rotational coordinate value is in rad/s and Translational in m/s.-->
<default_speed_value>0</default_speed_value>
<!--The minimum and maximum values that the coordinate can range between. Rotational coordinate range in radians and Translational in meters.-->
<range>-1 1</range>
<!--Flag indicating whether or not the values of the coordinates should be limited to the range, above.-->
<clamped>true</clamped>
<!--Flag indicating whether or not the values of the coordinates should be constrained to the current (e.g. default) value, above.-->
<locked>false</locked>
<!--If specified, the coordinate can be prescribed by a function of time. It can be any OpenSim Function with valid second order derivatives.-->
<prescribed_function />
<!--Flag indicating whether or not the values of the coordinates should be prescribed according to the function above. It is ignored if the no prescribed function is specified.-->
<prescribed>false</prescribed>
</Coordinate>
<Coordinate name="backpack_torso_tx">
<!--The value of this coordinate before any value has been set. Rotational coordinate value is in radians and Translational in meters.-->
<default_value>0</default_value>
<!--The speed value of this coordinate before any value has been set. Rotational coordinate value is in rad/s and Translational in m/s.-->
<default_speed_value>0</default_speed_value>
<!--The minimum and maximum values that the coordinate can range between. Rotational coordinate range in radians and Translational in meters.-->
<range>-1 1</range>
<!--Flag indicating whether or not the values of the coordinates should be limited to the range, above.-->
<clamped>true</clamped>
<!--Flag indicating whether or not the values of the coordinates should be constrained to the current (e.g. default) value, above.-->
<locked>false</locked>
<!--If specified, the coordinate can be prescribed by a function of time. It can be any OpenSim Function with valid second order derivatives.-->
<prescribed_function />
<!--Flag indicating whether or not the values of the coordinates should be prescribed according to the function above. It is ignored if the no prescribed function is specified.-->
<prescribed>false</prescribed>
</Coordinate>
</coordinates> |
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