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GTITRIM

GTITRIM

Name


  GTITRIM

Author


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

Purpose


  Normalize a Good Time Interval (GTI) - no overlapping and adjoining

Calling Sequence


  NEWGTI = GTITRIM(GTI, COUNT=, MAXGAP=, MINGTI=)

Description



  A good time interval is by definition a list of intervals which
  represent "good" or acceptable portions of the real number line.
  In this library a GTI is a 2xNINTERVAL array where NINTERVAL is
  the number of intervals.
  The numbers in the array represent the start and stop times of
  each interval. Thus, the array [[0,10],[20,30],[40,50]] represent
  intervals ranging from 0-10, 20-30 and 40-50. Formally, this
  example GTI represents times which would satisfy the following
  expression, for each time T and interval number i:
      T GE GTI(0,i) AND T LT GTI(1,i)
  Note that the endpoint is closed on the left but open on the
  right.
  However, not every 2xNINTERVAL array is a valid or "normalized"
  GTI as used by this library. The array must satisfy several
  conditions:
      * time ordered (ascending)
      * no overlapping intervals
      * no adjoining intervals (intervals that start and stop at the
        same point; e.g. the point 10 in this array [[0,10],[10,20]])
  A user who desires to create his or her own GTI array can proceed
  as follows.
  First, the array is placed in time order. This can be
  accomplished simply using the built-in function SORT. This
  statement sorts the array by start times.
      GTI = GTI(*, SORT(GTI(0,*)))
  Second, the GTITRIM function is used to fully normalize the set of
  intervals:
      GTI = GTITRIM(GTI)
  After these two procedures the GTI is considered valid and can be
  passed to the other routines of the library. Of course if the
  user can guarantee the above requirements without using GTITRIM
  then this is acceptable as well.
  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



  GTI - a 2xNINTERVAL array where NINTERVAL is the number of
        intervals. GTI(*,i) represents 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.

Keywords



  MAXGAP - Maximum allowable gap for merging existing good time
            intervals. Intervals with gaps smaller than MAXGAP will
            be combined into a single interval.
            Default: 0 (any gap keeps intervals separate)
  MINGTI - Minimum size interval. If any interval is smaller than
            MINGTI then it is discarded.
            Default: 0 (all intervals are preserved)
  COUNT - upon return, the number of resulting intervals. A value
          of zero indicates no good time intervals.

Returns



  A new GTI array containing the normalized 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



  GTIMERGE

Modification History


  Written, CM, 1997-2001
  Documented, CM, Apr 2001
  Corrected bug which bypassed MIN/MAXGTI, CM, 20 Jul 2003
  $Id: gtitrim.pro,v 1.7 2006/10/22 09:50:09 craigm Exp $



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