Adds arrows to plotting object

def add_arrows(self, cent, direction, mag=1, **kwargs):
        """ Adds arrows to plotting object """
        direction = direction.copy()
        if cent.ndim != 2:
            cent = cent.reshape((-1, 3))

        if direction.ndim != 2:
            direction = direction.reshape((-1, 3))

        direction[:,0] *= mag
        direction[:,1] *= mag
        direction[:,2] *= mag

        pdata = vtki.vector_poly_data(cent, direction)
        # Create arrow object
        arrow = vtk.vtkArrowSource()
        arrow.Update()
        glyph3D = vtk.vtkGlyph3D()
        glyph3D.SetSourceData(arrow.GetOutput())
        glyph3D.SetInputData(pdata)
        glyph3D.SetVectorModeToUseVector()
        glyph3D.Update()

        arrows = wrap(glyph3D.GetOutput())

        return self.add_mesh(arrows, **kwargs)