def datetime2mjd_tdb(date, obsvr_long, obsvr_lat, obsvr_hgt, dbg=False):
auinkm = 149597870.691
# Compute MJD_UTC from passed datetime
mjd_utc = datetime2mjd_utc(date)
if mjd_utc == None:
return None
# Compute MJD_TT
mjd_tt = mjd_utc2mjd_tt(mjd_utc, dbg)
# Compute TT->TDB
# Convert geodetic position to geocentric distance from spin axis (r) and from
# equatorial plane (z)
(r, z) = S.sla_geoc(obsvr_lat, obsvr_hgt)
ut1 = compute_ut1(mjd_utc, dbg)
if dbg:
print "UT1=", ut1
# Compute relativistic clock correction TDB->TT
tdb_tt = S.sla_rcc(mjd_tt, ut1, -obsvr_long, r * auinkm, z * auinkm)
if dbg:
print "(TDB-TT)=", tdb_tt
if dbg:
print "(CT-UT)=", S.sla_dtt(mjd_utc) + tdb_tt
mjd_tdb = mjd_tt + (tdb_tt / 86400.0)
return mjd_tdb
hdrs_needed = obtain_hdrpars(prihdr, debug)
# Compute TT midpoint of the exposure (in MJD)
hdrs_needed = compute_tt_mid(hdrs_needed, debug)
# Compute UT1
hdrs_needed = compute_ut1(hdrs_needed)
if debug: print hdrs_needed
# Need *geocentric* position of the observatory for the TDB clock
# correction so we have to convert from the geodetic position given
# by a GPS.
(r,z) = sla_geoc_iers2003(hdrs_needed['OBS_LAT'], hdrs_needed['OBS_HGT'])
# Calculate relativistic clock correction (TDB-TT) and put into dictionary
tdb_tt = S.sla_rcc(hdrs_needed['MJD_TT_mid'], hdrs_needed['UT1'],
-hdrs_needed['OBS_ELONG'], r, z)
tdb_utc = hdrs_needed['TT-UTC'] + tdb_tt
if debug: print 'TDB-TT(RCC)=', tdb_tt
if debug: print 'TDB-UTC =', tdb_utc
new_dict = { 'MJD_TDB_mid' : hdrs_needed['MJD_TT_mid'] + (tdb_tt/86400.0) }
hdrs_needed.update(new_dict)
# Compute star-independent parameters in preparation for
# conversions between mean place and geocentric apparent place.
amprms = S.sla_mappa(2000.0, hdrs_needed['MJD_TT_mid'])
# Reform into precession/nutation matrix
irmat = amprms[12:21].reshape(3,3)
# Earth's barycentric position (in AU) from sla_evp (max error 6900 km ~=23ms)
#pos_earth_bary = array([amprms[1],amprms[2],amprms[3]])
