How to retreive position and control move in SofaPython3?

[SalemTree]

I have tried the python code like this and "SofaTrainingScene-v15/16-python3-particle-interactive" , but still struggling with moving objects by changing its position.
In the "16-python3-particle-interactive" example, i tried to change self.CFF = kwargs.get("ForceField") to something like kwargs.get("position") to make it get position but apprantly it's not that simple.
Is there any example that I can refer to for controlling position with Sofapython3? Any help would be appreciated.

[hugtalbot]

Hi @SalemTree
the data field position (your degrees of freedom) are actually contained in the MechanicalObject, not in a forcefield.
To access it you would need a python pointer to your MechanicalObject and then you could do something like:

self.MO = kwargs.get("MechanicalObject")
print(str(self.MO.position))

However, what do you mean by "controlling position with Sofapython3" ? do you want to impose the position of some nodes ?

[hugtalbot]

was my input sufficient to you @SalemTree or do you need further guidance?

[SalemTree]

Hi @hugtalbot
Thanks for the example code!
I tried self.MO = kwargs.get("MechanicalObject") but it seems that it's not getting any object, when I print self.MO it shows "None". When I change it into self.CFF = kwargs.get("ForceField") it works perfectly well to print the force. Do you know what could be insufficient with the MechanicalObject part?

[damienmarchal]

Hi,

I think your problem come from a missunderstanding between what are sofa objects/nodes, how they are named, and the kwargs which are a python special structure used to stores "named argument" (if you are not used with that I recommend reading https://realpython.com/python-kwargs-and-args/)

Normally this is the classical pattern of code:

class MyController(Sofa.Core.Controller):
      def __init__(self, *args, **kwargs):                    # the ** means that the named argument passed to the constructor are stored in dictionnary called kwargs
                Sofa.Core.Controller.__init__(self, *args, **kwargs)
                self.MO = kwargs.get("targetMO")          # from the kwargs dictionnary you can then retrieve the one  with name "targetMO"
                
def createScene(root):
         root.addObject("MechanicalObject", name="mo1")      # create an object of type "MechanicalObject" having a name "mo1"
          
         root.addObject("XXXForceField", name="ff1")
         root.addObject(MyController(targetMO = root.mo1))   # You are passing the sofa object  'root.mo1' as the named argument "targetMO"

If you want kwargs.get("MechanicalObject") to suceed you need to do name your argument "MechanicalObject" like in the following

class MyController(Sofa.Core.Controller):
      def __init__(self, *args, **kwargs):                    # the ** means that the named argument passed to the constructor are stored in dictionnary called kwargs
                Sofa.Core.Controller.__init__(self, *args, **kwargs)
                self.MO = kwargs.get("MechanicalObject")          # from the kwargs dictionnary you can then retrieve the one  with name "MechanicalObject"
                
def createScene(root):
         root.addObject("MechanicalObject", name="mo1")
         root.addObject("XXXForceField", name="ff1")
         root.addObject(MyController(MechanicalObject = root.mo1))   # You are passing the sofa object  'root.mo1' as the named argument "MechanicalObject"

[SalemTree]

@damienmarchal
Yes! that is the missing part. After I name the argument in createScene it works.
Thank you so much!