gistfile1.py

def locatorOnPoly(name=""):
    """
    Requires a single poly selection.  The script will then create a locator of the polygon normal and then orient it
    to the tangent of the longest edge on the polygon using a aim constraint and and a couple of locators that finally
    get cleaned up.  Probably a nice way to do this by building a world space rotation matrix from the vector of
    point A and B on the longest edge and the normal of the poly.
    :param name: str(Locator Name)
    :return: pCore.dt.transform()
    """

    face = pCore.selected(fl=True)[0]

    if len(face) == 1:
        if isinstance(face, pCore.MeshFace):
            with pCore.UndoChunk():
                # Create the locator of the poly normal using the moveTool manipulator to do that
                currentTool = pCore.currentCtx()
                pCore.setToolTo("moveSuperContext")
                pos = pCore.dt.Vector(pCore.manipMoveContext("Move", q=1, p=1))
                pCore.setToolTo(currentTool)
                loc = pCore.spaceLocator(n="Average#")
                loc.setTranslation(pos)
                normal = face.getNormal(space="world")

                # reselect the face and get the perimeter edges
                pCore.select(face)
                pCore.mel.ConvertSelectionToEdgePerimeter()
                edgeList = pCore.selected(fl=True)

                # get the longest edges and pull out the world position of the start and end of that edge
                lengths = []
                for edge in edgeList:
                    lengths.append((edge.getLength(), edge))
                longestEdge = sorted(lengths)[-1][1]
                posA = longestEdge.getPoint(0, space="world")
                posB = longestEdge.getPoint(1, space="world")

                # Aim the locator using the some dummy locators
                locTemp = pCore.spaceLocator(n="tmp#")
                locTemp.setTranslation(posA)

                locTempB = pCore.spaceLocator(n="tmp#")
                locTempB.setTranslation(posB)

                # Make sure the Z Axis is the Primary Axis pointing along the normal.
                pCore.delete(pCore.aimConstraint(locTemp, locTempB, loc, aimVector=(1, 0, 0), upVector=(0, 0, -1), worldUpVector=normal))
                pCore.delete([locTemp, locTempB])

                if name:
                    loc.rename(name)

                return loc

def rivetLocatorToSelectedPoly(name=""):
    """
    Quick locator constrained to a Follicle.  Must have a single face selected
    :param name: str
    :return: None
    """
    face = pCore.selected()[0]
    if len(face) == 1:
        if isinstance(face, pCore.MeshFace):
            rivetLoc = locatorOnPoly(name)
            pCore.select(rivetLoc)
            pCore.move((0, 0, -0.005), r=1, os=1)  # moving off the surface doesn't improve.
            # Why does getUVAtPoint not work consistently?  This has started in Many scripts or even the closestPointOnMesh node
            # Running it once will return [0,0].  Noticed that when I ran it several times it returns the correct value,
            # eventually.  I though perhaps it was choosing a random direction + or - if one isn't given.
            u, v = [0, 0]
            for x in range(0):
                u, v = face.getUVAtPoint(rivetLoc.getRotatePivot(space="world"), "world", "map1")
                if any([u, v]):
                    break

            pCore.select([])
            pCore.select([rivetLoc, face])
            fTrans, fShape = createFollicle(rivetLoc.shortName(), poly_surface=face.node().name(), u=u, v=v)
            pCore.parentConstraint(fTrans, rivetLoc, mo=True)


def createFollicle(name, nurbs_surface=None, poly_surface=None, u=0, v=0):
    """
    Simple follicle creation wrapper.
    :param name: str
    :param nurbs_surface: str
    :param poly_surface: str
    :param u: int
    :param v: int
    :return: str(transform), str(follicleShape)
    """
    # create a follicle node and connect it
    follicle_transform = cmds.createNode("transform", n=(name + "follicle"))
    follicle = cmds.createNode("follicle", n=(name + "follicleShape"), p=follicle_transform)
    cmds.connectAttr((follicle + ".outTranslate"), (follicle_transform + ".translate"), f=1)
    cmds.connectAttr((follicle + ".outRotate"), (follicle_transform + ".rotate"), f=1)
    if nurbs_surface:
        cmds.connectAttr((nurbs_surface + ".local"), (follicle + ".is"), f=1)
        cmds.connectAttr((nurbs_surface + ".worldMatrix[0]"), (follicle + ".inputWorldMatrix"), f=1)
    if poly_surface:
        cmds.connectAttr((poly_surface + ".outMesh"), (follicle + ".inm"), f=1)
        cmds.connectAttr((poly_surface + ".worldMatrix[0]"), (follicle + ".inputWorldMatrix"), f=1)

    cmds.setAttr((follicle + ".parameterU"), u)
    cmds.setAttr((follicle + ".parameterV"), v)

    return follicle_transform, follicle

Thanks Andres, I've updated the code so you can see the complete picture.

Regards

David

I'm happy to hear it somehow works now and thanks for sharing the code. Funny that the one method call has 3 different possible modules that it comes from, my mistake! I wrote an API 2.0 version just in case you're interested (I know this was an issue that came from just having to update some scripts so I'm sure it's not retroactively helpful, but maybe going forward.):
https://gist.github.com/AndresMWeber/27ff60f361627d8bed1fa962929c37b8