Keywords: point

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## Description

The POINT program is a pointing parameter fitting program based on the SIC user interface, and GREG for graphic display. It is called by the command:

    $ POINT

A typical session with POINT is:

- `GREG1DEVICE RETRO`
  Define graphic device for display
- `FILE 16-OCT-1989 RADIO`
  Define the input data file and type. Three data types exist: RADIO, for single-dish radio pointing results, INTER for interferometric pointing results, and OPTICAL for optical pointing data. The file extension is derived from the data type using the following defaults : .RAD, .INT and .OPT respectively. .RAD files are produced by the CLASS `ANALYSEPRINT POINTING` command, .INT files are produced by the CLIC `CLICSOLVE POINTING` command, and .OPT files are produced by the DCL SAV command on the real-time microVAX BURE01. The data type also defines the default variable parameters.
- `READ 2`
  Read the data for Antenna 2 from the input file.
- `SOLVE`
  Solve for the pointing parameters using the currently read data.
- `PLOT SUMMARY`
  Display on the graphic device a summary of residual pointing errors; residual in Elevation versus residual in Azimuth.
- `PLOT COVERAGE`
  Display the Azimuth and Elevation coverage to see whether correlated parameters, such as `IAZ` and `COH` for example, are well determined or not.
- `PRINT/OUTPUT 16-OCT-1989.RADIO/HEADER`
  If both the summary and coverage look good, write the fit results to a file for the archive. The `/HEADER` option is used to write out the values of the fixed parameter also.

If some points appear discrepant in the fit or if the fit residuals are large, there are several possibilities for rejecting bad data points.

- `REJECT 8.0`
  Reject all data points with pointing residuals higher than after the last `SOLVE` command.
- `SET RMS 2.0`
  Select only those data points for which the formal error on the pointing observation is less than . For INTER and RADIO data types, the formal error is computed by the CLIC and CLASS gauss fit commands, and the error is set to zero for OPTICAL data.
- `SET ELEVATION 10.0 80.0`
  Select only data points in the elevation range 10 to 80 degrees. The default elevation range is 5 to 90 degrees.
- `IGNORE/SCAN s1 s2 s3 TO s4 BY s5/SOURCE JUPITER`
  Ignore some scans in the data (the scan numbers are displayed by the `PLOT SUMMARY` command), or some sources. Previously ignored scans and sources can be reconsidered agin using the `INCLUDE` command (same syntax as `IGNORE`).

If the coverage is bad, it is interesting to fix some parameter to reduce the errors on correlated parameters. This is especially true for the radio COH, because the collimation is essentially a constant that depends only on the antenna. For example

- `PARAMETER COH 42.0`
  Will fix `COH` to .
- `PARAMETER MVE/FREE`
  Will free the (previously fixed) parameter `MVE`.

Next: Optical versus Radio Up: The POINT program Previous: The POINT program Contents Index