Given treq, output index(ces) to extract via rawDMCreader
    treq: scalar or vector of ut1_unix time (seconds since Jan 1, 1970)
    ind: zero-based frame index corresponding to ut1_unix, corresponding to input data file.

def ut12frame(treq, ind, ut1_unix):
    """
    Given treq, output index(ces) to extract via rawDMCreader
    treq: scalar or vector of ut1_unix time (seconds since Jan 1, 1970)
    ind: zero-based frame index corresponding to ut1_unix, corresponding to input data file.
    """
    if treq is None:  # have to do this since interp1 will return last index otherwise
        return

    treq = atleast_1d(treq)
# %% handle human specified string scalar case
    if treq.size == 1:
        treq = datetime2unix(treq[0])
# %% handle time range case
    elif treq.size == 2:
        tstartreq = datetime2unix(treq[0])
        tendreq = datetime2unix(treq[1])
        treq = ut1_unix[(ut1_unix > tstartreq) & (ut1_unix < tendreq)]
    else:  # otherwise, it's a vector of requested values
        treq = datetime2unix(treq)
# %% get indices
    """
    We use nearest neighbor interpolation to pick a frame index for each requested time.
    """
    f = interp1d(ut1_unix, ind, kind='nearest', bounds_error=True,
                 assume_sorted=True)  # it won't output nan for int case in Numpy 1.10 and other versions too
    framereq = f(treq).astype(int64)
    framereq = framereq[framereq >= 0]  # discard outside time limits
    return framereq