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 3^rd 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):

1. The following two steps are performed prior to computing the telescope coordinates:
   1. Apply the pointing offsets computed by the POINTING_FOCUS task
   2. 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.

2. 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.

3. The RA & Dec of the source is computed as follows:
   1. Start with demand RA & Dec supplied by TCS configuration file
   2. 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
   3. Transform to geocentric apparent RA & Dec using slaMapqkz and the current target-independent mean-to-apparent parameters.

4. The RA & Dec of the telescope is computed as follows:
   1. Start with the demand Az/El coordinates as sent to the telescope hardware interface task
   2. Use the observatory location and slaDh2e to transform Az/El to HA/Dec
   3. Use the HA and current sidereal time to compute RA

5. 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.