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• In gtselect, the application of the data selections are made using the extended filename format of cfitsio.
  • For Pass 6 data, event class cuts were specified in via a filter string like this:

    Code Block
    "EVENT_CLASS >= 2"

    This was possible because the event classes were nested and the desired events could be selected using this filter.
  • For Pass7 data, the event classes are not nested at the less restrictive event selections, so it was decided that the EVENT_CLASS field would instead be interpreted as a bit field, with each bit indicating membership of an event to the corresponding event class. To select a given event class, a bit mask with the corresponding bit set is applied to the EVENT_CLASS variable:

    Code Block
    "((EVENT_CLASS/4)%2 == 1)"

    cfitsio does have the ability to apply a bit mask using "EVENT_CLASS & 4", but that requires the column in the FT1 file to be defined as a bit field. In the current definition, it is an integer.

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