TelCal Pointing/Reference Pointing

Pointing Introduction

  • The Pointing function in TelCal yields two distinct sets of data.
    • A Reference Pointing solution, which is multicast “to” the Executor.
    • A Pointing File (PNT) to be used by PEEK then Parminator to update the pointing offsets in the Parameters Database.
  • Reference Pointing and the Pointing File are solved simultaneously since about 95% of the calculations are the same.
  • Pointing only uses one subband of data.
    • This is the second subband if there are more than one, otherwise it uses the first.
  • The “Five Point Cross” algorithm is used to determine the offsets.
    • The center position and the two elevation offset positions' amplitudes are used to fit a parabola to determine the peek, which is then used to calculate the elevation offset from the current position.
    • Likewise, the center position and the two azimuth positions are used to determine the azimuth offset.
    • Each antenna is solved for independently.
    • Solutions are calculated when there is valid data (non-zero amplitudes) at each of the five pointing positions for a given antenna.
      • A solution may only contain a subset of antennas currently active in the observation.
      • There may only be one polarization (RCP or LCP) available depending on the Antsol solution provided.
  • The shared code path between Reference Pointing and the Pointing File diverge when we have solutions, by antenna and IF.
    • Note that all antennas and all IFs may not be represented in this intermediate solution.
    • This intermediate solution is logged to the PNTDTL file located in the TelCal logs directory.

TelCal Pointing Algorithm Description

TelCal collects antsol data to use for pointing if the scanIntent is set to CALIBRATE_POINTING. Each scan is independent. Currently, only data for the second subband (first if there is only one) is collected and used. When an antenna has one IF that has five points of valid (not zero amplitude), that antenna attempts to produce a pointing solution for all IFs then clears the cache of collected antsol data for this antenna.

Here is how a pointing solutions, for each IF, is calculated:
  1. Check for Flux error. If all five points have an amplitude less than 0.0003, trigger this error condition, but keep processing.
  2. Convert the amplitude at each position to ln(amplitude). This is because a log function maps better to the beam than a parabola does.
  3. Calculate the curvature of the fitting function: q = 2 * onPositionAmplitude - plusPositionAmplitude - minusPositionAmplitude. Do this twice; once for az and once for el. If q is negative for either az or el trigger a Fitting Function error, but keep processing.
  4. Calculate the pointing correction in native units: x = (plusPositionAmplitude - minusPositionAmplitude) / q / 2. Again, do this for az and el. q comes from step 3 above. If the correction is greater than 1 (meaning more than the throw, where throw is how far each position is from the onSource position), then trigger a Pointing Correction error, but keep processing.
  5. Calculate the estimated beam width: b = sqrt(2 / q). Again, once for az and once for el.
  6. Correct the estimated beam width for frequency: b = b * (skyFreq / ssloFreq). This correction is needed because we are observing at skyFreq but the throw is based on the ssloFreq. If the frequency-corrected estimated beam width is NOT in the range [0.85, 1.25] trigger a Beam Width error, but keep processing.
  7. All these calculated values are then logged and used in the two calculations below.

For the Peek pointing file (PNT), the solutions from IF_A and IF_B are averaged to come up with a single R polarization solution. The same thing is done for the L polarizations using IF_C and IF_D.

For the multicast, and the pgtsol file that logs it, the R and L solutions from Peek above are averaged to produce a single solution. If there are multiple solutions for an antenna within the same scan, subsequent solutions are averaged into previous solutions so that the average of all solutions for the scan is multicast/logged.

Reference Pointing Outline

  • Data Averaging
    • For each antenna, Reference Pointing averages the available IF solutions into RCP and LCP solutions.
      • Solutions for each IF are only included if they pass the following FOUR valid data checks:
        • FLUX – at least one position must have an amplitude greater than 0.0003.
        • FITTING_FUNCTION – The curvature of the parabola must be positive.
        • POINTING_CORRECTION – The pointing correction, in native units, must be less than 1.
        • BEAM_WIDTH – The estimated beam width must be in the range [1.5, 2.1].
          • The estimated beam width is corrected for frequency using:
            • estimated beam width *= (skyFreq/ssloFreq) ^ 2
    • Then the RCP and LCP solutions, if they both exist, are averaged together.
    • Finally, if this scan had a previous Reference Pointing solution, the current solution is averaged into the previous solutions.
  • The Reference Pointing solution is then multicast.
    • It is also logged to the *.ptgsol file.

Pointing File Creation Outline

  • Data Averaging
    • For each antenna, Pointing averages the available IF solutions into RCP and LCP solutions.
      • Solutions for each IF are only included if they pass the following TWO valid data checks:
        • FLUX – at least one position must have an amplitude greater than 0.0003.
        • FITTING_FUNCTION – The curvature of the parabola must be positive.
      • Pointing Correction and Beam Width errors are noted in the PNT file, but not excluded from the data.
      • Antennas end up on the Bad Antenna List in the PNT file for the following reasons:
        • The antenna has missing data (i.e. an expected IF is not provided by Antsol)
        • The estimated beam width is out of range
  • The Pointing solution is then written, by polarization, to the PNT file.

Example PNT file


//OFS1  10 151 08:09   J1331+30  X
//OFS2                     0.731596   17h33m29.893
//WX1  10 151 08:09        3.74     4.83   289.60  79055.00   268.52
//WX2  10 151 08:09        4.53
//SUB  1 OBSERVE FILE:
//SUB  2 DATA FILE:
//SUB  3 PROGRAM NAME: AW769_sb1194545_1_000
//SUB  4 SUBN:  26
//SUB 11 GDIDS1: 07 08 09 10 11 12 15 17 18 20 25 27
//SUB 14 BDIDS1: 01 03 04 13 19 21 28
01 R   0.6371   0.7707  -0.9717   0.2360 -0.078  1.948  0.116  1.962  0.081 F F
01 L   0.6371   0.7707  -0.9717   0.2360  0.126  1.934  0.229  2.100  0.096 F F
03 R   0.6371   0.7707  -0.9717   0.2360  0.042  1.946  0.288  2.255  0.068 F F
03 L   0.6371   0.7707  -0.9717   0.2360  0.210  1.943  0.373  2.307  0.091 F F
04 R   0.6371   0.7707  -0.9717   0.2360 -0.091  2.051  0.399  2.269  0.088 F F
04 L   0.6371   0.7707  -0.9717   0.2360  0.191  2.031  0.451  2.312  0.111 F F
07 R   0.6371   0.7707  -0.9717   0.2360 -0.135  1.955  0.000  1.923  0.113 F F
07 L   0.6371   0.7707  -0.9717   0.2360  0.019  1.898  0.059  1.986  0.104 F F
08 R   0.6371   0.7707  -0.9717   0.2360  0.055  1.875 -0.041  1.827  0.085 F F
08 L   0.6371   0.7707  -0.9717   0.2360  0.252  1.946  0.005  1.920  0.057 F F
09 R   0.6371   0.7707  -0.9717   0.2360 -0.163  1.740 -0.121  1.749  0.062 F F
09 L   0.6371   0.7707  -0.9717   0.2360 -0.013  1.779 -0.068  1.901  0.084 F F
10 R   0.6371   0.7707  -0.9717   0.2360 -0.155  1.906  0.044  1.810  0.047 F F
10 L   0.6371   0.7707  -0.9717   0.2360  0.092  1.853  0.129  1.835  0.058 F F
11 R   0.6371   0.7707  -0.9717   0.2360  0.177  1.902  0.076  1.965  0.159 F F
11 L   0.6371   0.7707  -0.9717   0.2360  0.414  1.907  0.095  1.979  0.174 F F
12 R   0.6371   0.7707  -0.9717   0.2360  0.205  1.979  0.012  1.928  0.097 F F
12 L   0.6371   0.7707  -0.9717   0.2360  0.436  1.956  0.079  1.891  0.098 F F
13 R   0.6371   0.7707  -0.9717   0.2360 -0.256  2.055  0.111  1.927  0.067 F F
13 L   0.6371   0.7707  -0.9717   0.2360 -0.052  2.005  0.172  1.965  0.061 F F
15 R   0.6371   0.7707  -0.9717   0.2360 -0.034  1.868 -0.297  1.827  0.112 F F
15 L   0.6371   0.7707  -0.9717   0.2360  0.194  1.889 -0.233  1.829  0.090 F F
17 R   0.6371   0.7707  -0.9717   0.2360  0.035  1.960  0.079  1.874  0.082 F F
17 L   0.6371   0.7707  -0.9717   0.2360  0.219  1.926  0.126  1.869  0.082 F F
18 R   0.6371   0.7707  -0.9717   0.2360 -0.222  1.993  0.122  1.922  0.101 F F
18 L   0.6371   0.7707  -0.9717   0.2360 -0.048  1.971  0.192  1.973  0.121 F F
19 R   0.6371   0.7707  -0.9717   0.2360 -0.226  2.127  0.057  2.035  0.138 F F
19 L   0.6371   0.7707  -0.9717   0.2360  0.061  1.920  0.100  1.873  0.104 F F
20 R   0.6371   0.7707  -0.9717   0.2360  0.239  1.981 -0.014  1.936  0.089 F F
20 L   0.6371   0.7707  -0.9717   0.2360  0.466  2.022  0.088  1.894  0.075 F F
21 R   0.6371   0.7707  -0.9717   0.2360 -0.048  2.011  0.056  2.156  0.124 F F
21 L   0.6371   0.7707  -0.9717   0.2360  0.239  1.964  0.140  2.044  0.083 F F
25 R   0.6371   0.7707  -0.9717   0.2360 -0.073  2.001  0.072  1.991  0.101 F F
25 L   0.6371   0.7707  -0.9717   0.2360  0.185  1.927  0.179  1.950  0.085 F F
27 R   0.6371   0.7707  -0.9717   0.2360  0.386  1.925  0.134  1.893  0.086 F F
27 L   0.6371   0.7707  -0.9717   0.2360  0.545  1.940  0.205  1.937  0.110 F F
28 R   0.6371   0.7707  -0.9717   0.2360 -0.630  2.264  0.047  1.917  0.074 F F
28 L   0.6371   0.7707  -0.9717   0.2360 -0.356  2.013  0.104  1.939  0.120 F F
ant pol cos(el) sin(el) cos(az) sin(az) El-offset BW Az Offset BW Flux OTT Shdwd

Example ptgsol file

DatasetID: AW769_sb1194545_1_000
MJD Bd Flgs Ant El Offset Az Offset Cnt
55347.33965277778  XX A    01    0.05737596   0.17356570 1
55347.33965277778  XX A    07   -0.05777006   0.02955385 1
55347.33965277778  XX A    08    0.15361241  -0.01812902 1
55347.33965277778  XX A    09   -0.08773367  -0.09438800 1
55347.33965277778  XX A    10   -0.03150851   0.08658360 1
55347.33965277778  XX A    11    0.29545701   0.08565884 1
55347.33965277778  XX A    12    0.32053125   0.04514699 1
55347.33965277778  XX A    13   -0.15541996   0.14149372 1
55347.33965277778  XX A    15    0.07997543  -0.26510316 1
55347.33965277778  XX A    17    0.12700309   0.10224275 1
55347.33965277778  XX A    18   -0.13504499   0.15686660 1
55347.33965277778  XX A    19   -0.02979551   0.08030988 1
55347.33965277778  XX A    20    0.35242438   0.03702614 1
55347.33965277778  XX A    21    0.10040706   0.09548243 1
55347.33965277778  XX A    25    0.05567408   0.12544799 1
55347.33965277778  XX A    27    0.46526673   0.16928524 1
55347.33965277778  XX A    28   -0.35568333   0.10449018 1
55347.33988425926  XX A    02    0.26229951   0.05973886 1
55347.33988425926  XX A    05    0.16438651  -0.16561542 1
55347.33988425926  XX A    14   -0.17478156   0.00306175 1
55347.33988425926  XX A    16    0.16550951   0.08599995 1
55347.33988425926  XX A    23    0.10268390   0.19080009 1
55347.33988425926  XX A    24   -0.11742006   0.05336944 1
55347.33988425926  XX A    26    0.17739642   0.11833081 1
55347.34023148148  XX A    01    0.01649326   0.10729542 2
55347.34023148148  XX A    03    0.05253665  -0.01702141 2
55347.34023148148  XX A    04   -0.01713075   0.09768221 2
55347.34023148148  XX A    07   -0.05255618   0.03497139 2
55347.34023148148  XX A    08    0.12651983  -0.03187969 2
55347.34023148148  XX A    09   -0.10014778  -0.13883156 2
55347.34023148148  XX A    10   -0.07470012   0.07013901 2
55347.34023148148  XX A    11    0.26233914   0.06024105 2
55347.34023148148  XX A    12    0.29181692   0.03683741 2
55347.34023148148  XX A    13   -0.16206792   0.13537621 2
55347.34023148148  XX A    15    0.07020764  -0.27904743 2
55347.34023148148  XX A    17    0.09312267   0.13168377 2
55347.34023148148  XX A    18   -0.15483882   0.14334625 2
55347.34023148148  XX A    19   -0.03982307   0.09736517 2
55347.34023148148  XX A    20    0.24546763   0.03014148 2
55347.34023148148  XX A    21    0.07676119   0.00648655 2
55347.34023148148  XX A    25    0.02693460   0.10191158 2
55347.34023148148  XX A    27    0.42091173   0.18099885 2
55347.34023148148  XX A    28   -0.40546024   0.08435959 2
55347.340462962966 XX A    02    0.22475295   0.05599536 2
55347.340462962966 XX A    05    0.13740492  -0.15315300 2
55347.340462962966 XX A    14   -0.19123137  -0.00024588 2
55347.340462962966 XX A    16    0.13169444   0.09396341 2
55347.340462962966 XX A    23    0.07002597   0.17824221 2
55347.340462962966 XX A    24   -0.13136092   0.05155994 2
55347.340462962966 XX A    26    0.12932663   0.10650549 2

-- JosephMcMullin - 11 Aug 2010
Topic revision: r1 - 2010-08-11, jmcmulli
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