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GTISEG

GTISEG

Name


  GTISEG

Author


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

Purpose


  Convert a list of times to a set of Good Time Intervals (GTIs)

Calling Sequence


  GTI = GTISEG(TIMES, COUNT=COUNT, INDICES=INDICES, $
                MAXGAP=MAXGAP, MINGTI=MINGTI)

Description



  The function GTISEG accepts an array of times and converts
  adjacent data into good time intervals (GTIs).
  Elements of the array are clustered into intervals based on the
  gaps between times. If the gaps are small enough then the times
  are grouped into a single interval. If a gap exceeds MAXGAP, then
  an interruption occurs and at least two intervals are formed.
  Thus, the keyword parameter MAXGAP essentially determines how many
  and where the intervals will be formed.
  If the time samples are regularly spaced -- aside from gaps --
  then MAXGAP should be set to a number slightly larger than the
  spacing to prevent roundoff errors. By default MAXGAP is set to
  the difference between the first and second samples.
  For GTISEG, the samples do not need to be regularly spaced, but
  they *must* be given in ascending order. Arrays can be sorted
  with the SORT function. The primary difference between GTISEG and
  MASK2GTI is that MASK2GTI assumes the time samples are regularly
  spaced while GTISEG does not. Also, MASK2GTI allows intervals to
  be enlarged or shrunk.
  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



  TIME - an array of times in ascending order.

Keywords



  MAXGAP - a scalar, the maximum gap between time samples before a
            new interval is created. Samples with gaps smaller than
            this value are grouped into a single GTI.
            Default: TIME(1) - TIME(0)
  MINGTI - the smallest possible GTI. Any interval smaller than
            MINGTI is discarded.
            Default: 0 (all intervals are accepted)
  COUNT - upon return, the number of resulting intervals. A value
          of zero indicates no good time intervals.
  INDICES - upon return, a 2xCOUNT array of integers which give the
            indices of samples which lie within each interval. The
            times TIME(INDICES(0,i) : INDICES(1,i)) fall within the
            ith interval.

Returns



  A new GTI array containing the enlarged or shrunken intervals.
  The array is 2xCOUNT where COUNT is the number of resulting
  intervals. GTI(*,i) represents the start and stop times of
  interval number i. The intervals are non-overlapping and
  time-ordered.
  If COUNT is zero then the returned array is a scalar value of
  zero, indicating no good intervals were found.

See Also



  MASK2GTI, GTITRIM, GTIMERGE, GTIWHERE

Modification History


  Written, CM, 1999-2001
  Documented, CM, Apr 2001
  MINGTI now works as documented, in that segments *equal* to MINGTI
    are now accepted, CM, 30 Oct 2007
  MINGTI now also affects INDICES, CM, 03 Mar 2008
  $Id: gtiseg.pro,v 1.7 2008/03/23 18:13:13 craigm Exp $



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