Pointing Data Format under TPOINT
Pointing Data Format under TPOINT
The acquisition of data in the
new TCS
produces a file called yyyymmdd-hhmmss.pnt in the summit
directory /jac_logs/yyyymmdd/yyyymmdd-hhmmss.pnt.
The format is TPOINT input version 1,
recording RAs & Decs and the LST rather than the multitude of telescope
parameters recorded under the
old TCS system.
Data is collected at the issuance of each SCUBA accept and (?) or
each heterodyne log.
An
example of the resulting pointing file, with a name like
         
20010109-060929.pnt
is shown below :
JCMT Pointing Test - 2001/01/09
: ALTAZ
+19 49 33.03 2001 01 10 1.63 629.68 4111.00 0.422 850.000
21 27 01.513 -15 44 14.45 21 27 02.905 -15 45 24.57 00 36.71610 85.342 56.197 SCUBA 0.00 0.00 0.1 2.6
21 27 01.610 -15 44 13.97 21 27 04.727 -15 45 29.94 00 48.26764 69.110 41.500 SCUBA 0.00 0.00 -0.7 1.4
22 53 59.103 +16 09 10.12 22 53 53.084 +16 07 41.56 01 10.91113 69.110 100.176 SCUBA 0.00 0.00 -1.0 0.3
22 53 59.103 +16 09 10.12 22 53 56.521 +16 07 37.43 02 9.85542 69.110 67.578 SCUBA 0.00 0.00 -1.6 0.1
22 53 59.103 +16 09 10.11 22 53 59.928 +16 07 34.90 03 3.59048 69.219 44.263 SCUBA 0.00 0.00 -3.6 -1.4
02 38 41.874 +16 37 11.27 02 38 31.030 +16 35 15.67 03 11.71182 69.110 169.017 SCUBA 0.00 0.00 -1.9 -0.8
04 31 42.014 +18 14 03.25 04 31 50.915 +18 14 24.10 03 18.51122 69.110 141.171 SCUBA 0.00 0.00 -3.7 -0.6
05 47 08.332 +00 21 42.27 05 47 13.042 +00 22 05.70 03 20.29108 69.110 79.181 SCUBA 0.00 0.00 -0.6 -0.4
05 23 00.982 -36 27 39.34 05 23 05.688 -36 26 47.65 03 30.56998 75.211 40.174 SCUBA 0.00 0.00 -1.3 1.4
05 35 17.732 -05 22 37.27 05 35 22.897 -05 22 41.46 03 35.08063 75.211 84.927 SCUBA 0.00 0.00 -2.0 -0.6
The 3rd line shows the observatory latitude, the UT date, the
atmospheric
temperature and pressure (mb), the observatory altitude in metres, local humidity
(%/100),
and the effective wavelength in microns.
Subsequent lines give the pointing data. The parameters displayed are as follows,
using the last entry as an example :
05 35 17.732 -05 22 37.27 05 35 22.897 -05 22 41.46 03 35.08063 75.211 84.927 SCUBA 0.00 0.00 -2.0 -0.6
-- RA & Dec of source --- --RA & Dec of telescope - ---- LST -- SMU-colln-offsets FE Instr.Ap.Offsets daz del
The following five Notes regarding the derivation of these terms were
provided by Russell Kackley (20071219):
- The following two steps are performed prior to computing the telescope
coordinates:
- Apply the pointing offsets computed by the POINTING_FOCUS task
- Examine the current instrument aperture in the TCS. If the aperture
involves the use of a tracking receptor, change the instrument
aperture
to the (0,0) aperture location. We do this because TPOINT cannot
handle aperture offsets. The aperture is reset to the original
location after recording the information in the .pnt file.
- The observatory latitude has been corrected for polar motion, using:
lat = lat + xpmr*cos(longit) - ypmr*sin(longit)
where the uncorrected latitude is 0.346026069 radians, longitude is
-2.713633073 radians, and (xpmr, ypmr) are from the IERS tables.
- The RA & Dec of the source is computed as follows:
- Start with demand RA & Dec supplied by TCS configuration file
- Correct RA & Dec for proper motion using slaPm with ep0 = the epoch
in which the source coordinates were supplied and ep1 = current
barycentric dynamical time
- Transform to geocentric apparent RA & Dec using slaMapqkz and the
current target-independent mean-to-apparent parameters.
- The RA & Dec of the telescope is computed as follows:
- Start with the demand Az/El coordinates as sent to the telescope
hardware interface task
- Use the observatory location and slaDh2e to transform Az/El to
HA/Dec
- Use the HA and current sidereal time to compute RA
- The demand Az/El coordinates sent to the telescope are computed by
starting with the demand RA & Dec supplied by TCS configuration file,
transforming to Az/El, and applying corrections for the Earth rotation,
diurnal aberration, refraction, the telescope pointing model, and current
pointing model offsets.
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