[SOLVED] Export Object velocity and position values in each time step

[Thresholddd]

Hi, everyone,
I am new to Sofa. I currently use Sofa v21.06 binaries and sofaPython3 in windows 10. Now I want to export nodes’ positions and velocity in each timestep. Do you know how to do that?

Thanks very much!

Regards,
Yuan

[Hugo]

Hi @qdyuan4619

welcome to the SOFA forum then!
You can either use one of the Exporter in SOFA like the MeshVTKExporter (see example here).

Or you could use python to access data field (“positions” and “velocity”) of the MechanicalObject and write then into any format/file you’d like.

Best wishes,

Hugo

[Thresholddd]

Hi, @Hugo,
Thanks you for your advice, I read the examples about writing data and successfully record states by using monitor or VtkExamples, but I have one question left that I do not know how to access data field in python. I did not find related examples in sofaPython3 and sofa. Thanks very much for your help!

Yuan

[Hugo]

Hi @qdyuan4619

You can take a look at this example I wrote. A python controller is added in the scene and it accesses data in the scene like the totalForce data of a ConstantForceField as shown in the onKeypressedEvent() function of the controller.

import sys
import Sofa

class ManageParticles(Sofa.Core.Controller):

    def __init__(self, *args, **kwargs):
        # These are needed (and the normal way to override from a python class)
        Sofa.Core.Controller.__init__(self, *args, **kwargs)
        self.CFF = kwargs.get("ForceField")
        self.rootNode = kwargs.get("rootNode")
        self.iteration = 1

    def onKeypressedEvent(self, event):
        key = event['key']

        if key=="+" :
            with self.CFF.totalForce.writeableArray() as wa:
                wa[0] += 0.01

        if key=="-" :
            with self.CFF.totalForce.writeableArray() as wa:
                wa[0] -= 0.01

        return 0;

def createScene(node):
    node.addObject('RequiredPlugin', name="SIOS-load", pluginName="SofaImplicitOdeSolver")
    node.addObject('RequiredPlugin', name="SBC-load",  pluginName="SofaBoundaryCondition")
    node.dt = 0.01
    node.gravity = [0,0,0]

    Particle = node.addChild('Particle-0')
    Particle.addObject('EulerImplicitSolver')
    Particle.addObject('CGLinearSolver', threshold='1e-09', tolerance='1e-09', iterations='200')
    Particle.addObject('MechanicalObject', showObject='1', position='0 0 0    0 0 0 1', name='Particle-0', template='Rigid3d')
    Particle.addObject('UniformMass', totalMass='1')
    Particle.addObject('ConstantForceField', name="CFF", totalForce="0 0 0 0 0 0" )

    node.addObject( ManageParticles(name="MyParticlesController", ForceField=Particle.CFF, rootNode=node) )

    return 0;

def main():
    import SofaRuntime
    import Sofa.Gui
    # Make sure to load all SOFA libraries
    SofaRuntime.importPlugin("SofaBaseMechanics")
    SofaRuntime.importPlugin("SofaOpenglVisual")

    #Create the root node
    root = Sofa.Core.Node("root")
    # Call the below 'createScene' function to create the scene graph
    createScene(root)
    Sofa.Simulation.init(root)

    # Launch the GUI (qt or qglviewer)
    Sofa.Gui.GUIManager.Init("myscene", "qglviewer")
    Sofa.Gui.GUIManager.createGUI(root, __file__)
    Sofa.Gui.GUIManager.SetDimension(1080, 1080)
    # Initialization of the scene will be done here
    Sofa.Gui.GUIManager.MainLoop(root)
    Sofa.Gui.GUIManager.closeGUI()

    print("Simulation is done.")

# Function used only if this script is called from a python environment
if __name__ == '__main__':
    main()

Best wishes,

Hugo

[Thresholddd]

Hi, @Hugo,

Thank you for your example! I will try it and mark this problem as solved! Thank you very much again!

Best wishes,
YUAN

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