Name

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  GTI2MASK
 

Author

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  Craig B. Markwardt, NASA/GSFC Code 662, Greenbelt, MD 20770
  craigm@lheamail.gsfc.nasa.gov

Purpose

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  Convert Good Time Interval (GTI) to evenly sampled mask array

Calling Sequence

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  MASK = GTI2MASK(GTI, [TIME, TLIMITS=, TIMEDEL=, NTBINS=,
                  GOOD=, BAD=, /FILL, /INVERT])

Description

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  The function GTI2MASK converts an existing valid Good Time
  Interval (GTI) array to a mask array. By definition a GTI
  indicates an array of intervals which are not on an evenly sampled
  array. This routine either accepts a time grid from the user, or
  the grid must be described by the TLIMITS and TIMEDEL keywords.
  The output mask array describes whether each grid point lies
  within a good interval or not. There is full control over the
  values of the good and bad values.
  This routine is the inverse of MASK2GTI.
  It should be noted that this function is not constrained to
  operation only on time arrays. It should work on any
  one-dimensional quantity with intervals.

Inputs

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  GTI - a 2xNINTERVAL array where NINTERVAL is the number of
        intervals. GTI(*,i) represent the start and stop times of
        interval number i. The intervals must be non-overlapping
        and time-ordered (use GTITRIM to achieve this).
        A scalar value of zero indicates that the GTI is empty, ie,
        there are no good intervals.
  TIME - optional time array that specifies the time grid for the
          mask array. If TIME is not specified then the user must
          give the TLIMITS and TIMEDEL keywords to fully describe the
          grid spacing. The TIME array is overwritten if the FILL
          keyword is used.

Keywords

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  TLIMITS - a 2-element array giving the start and stop limits over
            which the mask array is to be generated. The TLIMITS
            and TIMEDEL keywords are required if the TIME parameter
            is not given.
  TIMEDEL - a scalar specifying the interval between grid points.
            The TLIMITS and TIMEDEL keywords are required if the
            TIME parameter is not given.
  NTBINS - upon return, this keyword contains the number of time
            samples created.
  GOOD - the value of "good" in the output mask array.
          Default: 1b
  BAD - the value of "bad" in the output mask array.
        Default: 0b
  INVERT - if set, the array GTI is treated as a "bad" time
            interval, ie, the GOOD and BAD values are swapped.
  FILL - if set, the array TIME is filled with values determined
          from the TLIMITS and TIMEDEL keyword.

Returns

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  A mask array, either sampled at the points specified by TIME, or
  by the grid specified by TLIMITS and TIMEDEL. The "good" value
  indicates that the point lies within the good interval, while a
  "bad" value indicates the point was outside.

See Also

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  MASK2GTI, GTITRIM, GTIMERGE

Modification History

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  Written, CM, 1997-2001
  Documented, CM, Apr 2001
  Add internal OVERLAP and MINFRACEXP keywords, CM, 03 Feb 2007
  Refine and simplify the OVERLAP processing, CM, 14 Feb 2007
  Handle case of /OVERLAP when there is no intersection, CM, 22 Aug 2007
  Use VALUE_LOCATE for performance (in non-OVERLAP case), CM, 04 May 2008