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 heterodyne log.

An example of the resulting pointing file, with a name like

          20090128-235843.pnt

is shown below :

JCMT Pointing Test - 2009/01/28
: ALTAZ
+19 49 22.30  2009 01 29    -2.25  621.00   4120.00   0.827   866.963
09 48 29.174 +13 14 02.63  09 48 35.756 +13 15 09.01   08 12.04958    4.760  108.775 HARPB    0.00    0.00    1.9    2.6
09 48 29.174 +13 14 02.63  09 48 36.988 +13 14 31.52   08 37.90685   -1.266  124.686 HARPB    0.00    0.00    2.5    0.4
07 23 22.817 -25 47 11.45  07 23 37.834 -25 49 16.26   09  1.52885   -1.400   53.730 HARPB    0.00    0.00   -0.3    5.1
07 23 22.816 -25 47 11.46  07 23 38.266 -25 50 07.28   10  6.12021   -1.400   40.427 HARPB    0.00    0.00   -2.2    0.3
09 48 29.175 +13 14 02.63  09 48 25.106 +13 11 47.59   10 31.05245   -1.400  142.134 HARPB    0.00    0.00    2.9    3.6
05 18 04.613 +53 35 58.94  05 18 20.552 +53 31 13.78   10 52.60965   -1.400   29.219 HARPB    0.00    0.00   -1.2   -0.5
05 18 04.612 +53 35 58.95  05 18 22.694 +53 31 15.81   10 59.29623   -1.400   28.202 HARPB    0.00    0.00   -2.1    4.6
12 45 35.318 +45 23 03.10  12 45 24.203 +45 24 20.18   12 21.49399   -1.400  105.967 HARPB    0.00    0.00    1.5   -0.1
12 45 35.321 +45 23 03.11  12 45 21.284 +45 21 46.28   14  9.76879   -1.400   95.100 HARPB    0.00    0.00    3.0    1.8

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 :

12 45 35.321 +45 23 03.11  12 45 21.284 +45 21 46.28   14  9.76879    -1.400   95.100   HARPB    0.00    0.00     3.0  1.8
-- RA & Dec of source ---  --RA & Dec of telescope--   --- LST ---   SMU-colln-offsets   FE    Instr.Ap.Offsets   uaz  uel

Note: uaz and uel are the offsets from the current pointing model in azimuth and elevation.

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.