def wnunid(a, b):
    """
    Place the union of two double precision windows into a third window.

    http://naif.jpl.nasa.gov/pub/naif/toolkit_docs/C/cspice/wnunid_c.html

    :param a: Input window A. 
    :type a: spiceypy.utils.support_types.SpiceCell
    :param b: Input window B. 
    :type b: spiceypy.utils.support_types.SpiceCell
    :return: Union of a and b.
    :rtype: spiceypy.utils.support_types.SpiceCell
    """
    assert isinstance(a, stypes.SpiceCell)
    assert b.dtype == 1
    assert isinstance(b, stypes.SpiceCell)
    assert a.dtype == 1
    c = stypes.SpiceCell.double(b.size + a.size)
    libspice.wnunid_c(ctypes.byref(a), ctypes.byref(b), ctypes.byref(c))
    return c