Interpolation/Extrapolation Tolerance

Clearly there is some limit to the interval of time over which you can sensibly interpolate or extrapolate gains. If the gap between the secondary observations is too large, then the interpolation of the gain solutions may have no resemblance to the true gains at a given time. The software that interpolates or extrapolates between the gain solutions has a tolerance which limits the gaps in time that it will permit. If the time differences between a source observation and two gain solutions bounding it are both less than the tolerance, then the program source gain is the interpolation of the two gain solutions. If there is only one gain solution within the time tolerance, then this is used without any interpolation. If there are no gains within the time tolerance, the corresponding program source data are marked as flagged.

This interpolation tolerance is stored as the interval item the visibility dataset. It is given as a double precision number with units of days. Task gpcal sets its value as half a day (interval=0.5). Though this is excessively generous, this will not be a problem unless there are large gaps between calibrator scans (perhaps because some calibrator scans had to be discarded). You can set the set the interpolation tolerance using puthd. For example

in=vela.4800/interval Set the interpolation tolerance of
  dataset vela.4800.
value=0.1 Set the tolerance to 2.4 hours (0.1 days).

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