def create_field_plane_visibility(fieldmodule, finite_element_field,
    plane_normal_field, point_on_plane_field):
    """
    Create a visibility field that is based on the plane equation.
    """
    d = fieldmodule.createFieldSubtract(finite_element_field,
        point_on_plane_field)
    p = fieldmodule.createFieldDotProduct(d, plane_normal_field)
    t = fieldmodule.createFieldConstant(0.1)
    v = fieldmodule.createFieldLessThan(p, t)
    return v
