How to gather pole vector position

Get the pole vector using three positions.

First we write the function using Maya's OpenMaya MVector class to help us with doing the math. Below is a function which takes three non-default arguments which are the three points in space to use for the calculation. 

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from maya import OpenMaya

def getPoleVectorPosition(startPnt, middlePnt, endPnt, scaler=1):
    '''
    This will return the position for where the pole vector location is.

    :param startPnt: The first point to use for locating the pole vector.
    :type startPnt: list | tuple | MPoint | MVector

    :param middlePnt: The second point to use for locating the pole vector.
    :type middlePnt: list | tuple | MPoint | MVector

    :param endPnt: The final point to use for locating the pole vector.
    :type endPnt: list | tuple | MPoint | MVector

    :return: Position for the pole vector
    :rtype: tuple
    '''
    # Here we will do some type checking.
    for pnt in (startPnt,middlePnt,endPnt):
        if not isinstance(pnt,(list,tuple,OpenMaya.MPoint)):
            raise TypeError('{0} is must be one of the following type: list, tuple, MPoint, MVector'.format(pnt))

    # MVectors
    startVector = OpenMaya.MVector(startPnt[0],startPnt[1],startPnt[2])
    middleVector = OpenMaya.MVector(middlePnt[0],middlePnt[1],middlePnt[2])
    endVector = OpenMaya.MVector(endPnt[0],endPnt[1],endPnt[2])
    
    # This is the vector from origin to the exact point between the
    # start and end points passed in.
    midVector = (startVector + endVector) / 2
    
    # scale the vector by using the scaler passed in by the user.
    diffVectorScaled = (middleVector - midVector) * scaler
    
    # now we get the pole vector with the scale already included.
    poleVector = midVector + diffVectorScaled
    
    return (poleVector.x, poleVector.y, poleVector.z)
First we create the joints and position them. 

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from maya import cmds
upperArmL=cmds.joint(name='upperArm_l_bind',position=(1,5,0))
lowerArmL=cmds.joint(name='lowerArm_l_bind',position=(6,5,-2))
wristL=cmds.joint(name='wrist_l_bind',position=(5,11,0))
Even though we know the positions of the joints. I will query them using the xform command. 

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upperArmLPnt=cmds.xform(upperArmL,q=True,ws=True,t=True)
lowerArmLPnt=cmds.xform(lowerArmL,q=True,ws=True,t=True)
wristLPnt=cmds.xform(wristL,q=True,ws=True,t=True)
Now we will just pass those positions into the function we wrote above and use it to position a new joint. 

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poleVectorPnt = getPoleVectorPosition(upperArmLPnt,lowerArmLPnt,wristLPnt)

cmds.joint(name='pv_l_ik',position=poleVectorPnt)

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