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Add calc methods and Outputs for whole-body momentum to Model #3487

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merged 7 commits into from
Jun 20, 2023
Merged

Add calc methods and Outputs for whole-body momentum to Model #3487

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1a9e777
Add momentum outputs to Model
nickbianco Jun 16, 2023
11f0207
Update changelog
nickbianco Jun 16, 2023
c88b222
Style improvement
nickbianco Jun 19, 2023
00287ca
Merge branch 'main' into wbam_output
nickbianco Jun 19, 2023
92753bc
Remove realize calls for COM methods
nickbianco Jun 19, 2023
ca880af
Add back realize calls in COM methods
nickbianco Jun 20, 2023
2a9d509
Move Doxygen comments to the header file // add realize call to the m…
nickbianco Jun 20, 2023
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1 change: 1 addition & 0 deletions CHANGELOG.md
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Expand Up @@ -35,6 +35,7 @@ v4.5
- Fixed runtime segfault that can occur when trying to use a `WrapObject` that is not a child of a `PhysicalFrame` (#3465)
- Fixed issues #3083 #2575 where analog data is not pulled out from c3d files, a a new function getAnalogDataTable() has been added to the C3DFileAdapter
- Fixed segfault that can occur when building models with unusual joint topologies (it now throws an `OpenSim::Exception` instead, #3299)
- Add `calcMomentum`, `calcAngularMomentum`, `calcLinearMomentum`, and associated `Output`s to `Model` (#3474)


v4.4
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23 changes: 23 additions & 0 deletions OpenSim/Simulation/Model/Model.cpp
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Expand Up @@ -2222,6 +2222,29 @@ SimTK::Vec3 Model::calcMassCenterAcceleration(const SimTK::State &s) const
getMultibodySystem().realize(s, Stage::Acceleration);
return getMatterSubsystem().calcSystemMassCenterAccelerationInGround(s);
}
/**
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These Doxygen-style comments don't get picked up from the .cpp file (only the headers). See, for example, the (blank) documentation for Model::calcMassCenterPosition() (notably, the potentially useful comment "Return the position vector of the system mass center, measured from the Ground origin, and expressed in Ground." does not appear). Perhaps at least put the Doxygen comments for your new methods in the header file, and create an Issue to move the others.

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Good catch! I can move all these over.

* Return the spatial momentum about the system mass center expressed in Ground.
*
*/
SimTK::SpatialVec Model::calcMomentum(const SimTK::State &s) const
{
return getMatterSubsystem().calcSystemCentralMomentum(s);
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Following the examples above (e.g., Model::calcMassCenterAcceleration()), shouldn't this line be preceded by

getMultibodySystem().realize(s, Stage::Velocity);

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(I think the realize() calls should be here since an API user might call the method directly. IIRC, calling realize() isn't [supposed to be] expensive if the State has already been realized to the required Stage.)

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I thought it was weird these calls were inside the calc-COM methods, but I think you're right, the Stage is probably cached and realize won't re-realize if it is. (I also tried taking out the realize calls in the calc-COM methods and it broke some tests, so there's that.)

}
/**
* Return the angular momentum about the system mass center expressed in Ground.
*
*/
SimTK::Vec3 Model::calcAngularMomentum(const SimTK::State& s) const {
return getMatterSubsystem().calcSystemCentralMomentum(s).get(0);
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Mostly a style suggestion, but may make future maintenance simpler. (and same for calcLinearMomentum if accepted)

Suggested change
return getMatterSubsystem().calcSystemCentralMomentum(s).get(0);
return calcMomentum(s).get(0);

}
/**
* Return the linear momentum expressed in Ground.
*
*/
SimTK::Vec3 Model::calcLinearMomentum(const SimTK::State& s) const {
return getMatterSubsystem().calcSystemCentralMomentum(s).get(1);
}


/**
* Construct outputs
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14 changes: 13 additions & 1 deletion OpenSim/Simulation/Model/Model.h
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Expand Up @@ -237,7 +237,16 @@ OpenSim_OBJECT_NONTEMPLATE_DEFS(Model, ModelComponent);
calcKineticEnergy, SimTK::Stage::Position);

OpenSim_DECLARE_OUTPUT(potential_energy, double,
calcPotentialEnergy, SimTK::Stage::Velocity);
calcPotentialEnergy, SimTK::Stage::Velocity);

OpenSim_DECLARE_OUTPUT(momentum, SimTK::SpatialVec,
calcMomentum, SimTK::Stage::Velocity);

OpenSim_DECLARE_OUTPUT(angular_momentum, SimTK::Vec3,
calcAngularMomentum, SimTK::Stage::Velocity);

OpenSim_DECLARE_OUTPUT(linear_momentum, SimTK::Vec3,
calcLinearMomentum, SimTK::Stage::Velocity);


//=============================================================================
Expand Down Expand Up @@ -833,6 +842,9 @@ OpenSim_OBJECT_NONTEMPLATE_DEFS(Model, ModelComponent);
SimTK::Vec3 calcMassCenterPosition(const SimTK::State &s) const;
SimTK::Vec3 calcMassCenterVelocity(const SimTK::State &s) const;
SimTK::Vec3 calcMassCenterAcceleration(const SimTK::State &s) const;
SimTK::SpatialVec calcMomentum(const SimTK::State &s) const;
SimTK::Vec3 calcAngularMomentum(const SimTK::State &s) const;
SimTK::Vec3 calcLinearMomentum(const SimTK::State &s) const;
/** return the total Kinetic Energy for the underlying system.*/
double calcKineticEnergy(const SimTK::State &s) const {
return getMultibodySystem().calcKineticEnergy(s);
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