Maya: Connect Objects translation to param u on NurbsCurve via pointOnCurveInfo node.

maya_connect_objects_to_nurbscurve_pointoncurveinfo.py

"""Connect objects (transforms) to a nurbsCurve by pointOnCurve node.

Select the objects, then select the nurbsCurve last.
Run the script.
Voila.

Updated version of: https://polycount.com/discussion/161754/eye-rig-script-problem

""" 

from maya import cmds
import maya.api.OpenMaya as om2


def get_dag_path(node_name):
    """Return maya.api.OpenMaya.MDagPath from node name.
    
    Args:
        node_name (str): Maya dag node name.
    
    Returns:
        om2.MDagPath: Dag path for the node.
    
    """
    sel = om2.MSelectionList()
    sel.add(node_name)
    return sel.getDagPath(0)


def get_curve_u_param(pos, crv, tolerance=0.001):
    """Return closest U param on the nurbs curve.

    Args:
        pos  (list): Vector of position.
        curve (str): Name of the curve shape node.

    Returns:
        float: U Param.
    """

    point = om2.MPoint(pos)

    dag = get_dag_path(crv)
    dag.extendToShape()  # make sure to use the shape of the curve

    fn_curve = om2.MFnNurbsCurve(dag)
    if fn_curve.isPointOnCurve(point):
        return fn_curve.getParamAtPoint(point, tolerance, om2.MSpace.kObject)
    else:
        point, param = fn_curve.closestPoint(point, 
                                             tolerance=tolerance, 
                                             space=om2.MSpace.kObject)
        return fn_curve.getParamAtPoint(point, tolerance, om2.MSpace.kObject)


sel = cmds.ls(selection=True, long=True)

if len(sel) < 2:
    raise RuntimeError("Select objects first and the nurbsCurve last. You must select at least two objects.")

# Last object in selection will be used as curve
crv = sel.pop()

for node in sel:
    pos = cmds.xform(node, query=True, worldSpace=True, translation=True)
    u = get_curve_u_param(pos, crv)
    name = node.rsplit("|", 1)[-1].replace("_LOC", "_PCI")
    pci = cmds.createNode("pointOnCurveInfo", name=name)
    cmds.connectAttr(crv + ".worldSpace", pci + ".inputCurve")
    cmds.setAttr(pci + ".parameter", u)
    cmds.connectAttr(pci + ".position", node + ".translate")

print("Connected objects to curve '{}':\n -{}".format(crv, "\n -".join(sel)))