Running StaticOptimization from C++

[Felix Laufer]

Hi everyone,

I know what static optimization does, which artifacts it requires and how it is executed using the OpenSim GUI.
However, I have no idea how to run it using the API via C++. There are many C++ and Python
examples but as far as I know none covers static optimization. Is there any minimal working example?
Particularly, I wonder how to specify the motion trajectories, the external GRFs and add them to the SO-Object.

Thanks & best regards
Felix

[Dimitar Stanev]

Hi,

This is the code that I use with OpenSim 3.3 and Python:

Code: Select all

def perform_so(model_file, ik_file, grf_file, grf_xml, reserve_actuators,
               results_dir):
    """Performs Static Optimization using OpenSim.

    Parameters
    ----------
    model_file: str
        OpenSim model (.osim)
    ik_file: str
        kinematics calculated from Inverse Kinematics
    grf_file: str
        the ground reaction forces
    grf_xml: str
        xml description containing how to apply the GRF forces
    reserve_actuators: str
        path to the reserve actuator .xml file
    results_dir: str
        directory to store the results
    """
    # model
    model = opensim.Model(model_file)

    # prepare external forces xml file
    name = os.path.basename(grf_file)[:-8]
    external_loads = opensim.ExternalLoads(model, grf_xml)
    external_loads.setExternalLoadsModelKinematicsFileName(ik_file)
    external_loads.setDataFileName(grf_file)
    external_loads.setLowpassCutoffFrequencyForLoadKinematics(6)
    external_loads.printToXML(results_dir + name + '.xml')

    # add reserve actuators
    force_set = opensim.ForceSet(model, reserve_actuators)
    force_set.setMemoryOwner(False)  # model will be the owner
    for i in range(0, force_set.getSize()):
        model.updForceSet().append(force_set.get(i))

    # construct static optimization
    motion = opensim.Storage(ik_file)
    static_optimization = opensim.StaticOptimization()
    static_optimization.setStartTime(motion.getFirstTime())
    static_optimization.setEndTime(motion.getLastTime())
    static_optimization.setUseModelForceSet(True)
    static_optimization.setUseMusclePhysiology(True)
    static_optimization.setActivationExponent(2)
    static_optimization.setConvergenceCriterion(0.0001)
    static_optimization.setMaxIterations(100)
    # model.addAnalysis(static_optimization)
    model.updAnalysisSet().adoptAndAppend(static_optimization)

    # analysis
    analysis = opensim.AnalyzeTool(model)
    analysis.setName(name)
    analysis.setModel(model)
    analysis.setInitialTime(motion.getFirstTime())
    analysis.setFinalTime(motion.getLastTime())
    analysis.setLowpassCutoffFrequency(6)
    analysis.setCoordinatesFileName(ik_file)
    analysis.setExternalLoadsFileName(results_dir + name + '.xml')
    analysis.setLoadModelAndInput(True)
    analysis.setResultsDir(results_dir)
    analysis.run()
    so_force_file = results_dir + name + '_StaticOptimization_force.sto'
    so_activations_file = results_dir + name + \
        '_StaticOptimization_activation.sto'
    return (so_force_file, so_activations_file)

There are some minor differences between v3.3 and v4.0 and I didn't had time to migrate my scripts yet.

https://github.com/opensim-org/opensim-core/issues/2076

[Felix Laufer]

Great! Thank you very much!