The I-task Interface File

The I-task has a parameter FILTER_DEMAND which specifies the required filter and an action FILTER which moves the filter wheel to the required position. These are specified in the interface file for the task as follows:

    PARAMETER FILTER_DEMAND
      TYPE '_CHAR'
      VPATH 'INTERNAL'
      IN 'U','B','V','R','I'
    ENDPARAMETER

    ACTION FILTER
      OBEY
        NEEDS FILTER_DEMAND
      ENDOBEY
      CANCEL
      ENDCANCEL
    ENDACTION

Many I-task parameters have VPATH specified as 'INTERNAL' - this means that the parameter value is stored in memory for speed of access. The IN field specifies the valid values for the parameter (it is also possible to use a RANGE specification to restrict the values of a parameter).

The action entry specifies that the action FILTER may be obeyed and cancelled, and that they OBEY action needs the parameter FILTER_DEMAND which may be specified as the first (only) parameter on the command line.