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GTIENLARGE

GTIENLARGE

Name


  GTIENLARGE
 

Author


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

Purpose


  Enlarge (or shrink) each Good Time Interval (GTI) by fixed amounts

Calling Sequence


  NEWGTI = GTIENLARGE(GTI, COUNT=COUNT, PRE=PRE, POST=POST)

Description



  The function GTIENLARGE accepts an existing valid Good Time
  Interval (GTI) array and creates a new GTI array in which the
  intervals have been enlarged (or shrunken) by a fixed amount.
  The keywords PRE and POST are used to specify the enlargement.
  Given an existing good interval such as this one:
                  100 200 GTI=[[100,200]]
      <------------|===================|------------->
  a positive value of PRE will enlarge the lead edge of the interval
  and a positive value of POST will enlarge the trailing edge of the
  interval. Thus PRE=10 and POST=20 will create a new interval from
  the above example:
              90<-- --->220 NEWGTI=[[ 90,220]]
      <---------|==.===================.====|-------->
            PRE=10 POST=20
  Negative values of PRE and POST are allowed, which will shrink the
  interval from the leading and trailing edges respectively.
  Users should be aware that the number of intervals may shrink
  under this operation, since it is possible either for two
  intervals to be merged if they are enlarged and overlap, or if
  they are shrunken to a size of zero.
  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



  PRE - the amount each interval should be enlarged from its leading
        edge. A negative value indicates the interval should
        shrink.
        Default: 0
  POST - the amount each interval should be enlarged from its
          trailing edge. A negative value indicates the interval
          should shrink.
          Default: 0
  COUNT - upon return, the number of resulting intervals. A value
          of zero indicates no good time intervals.

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



  GTITRIM, GTIENLARGE

Modification History


  Written, CM, 1997-2001
  Documented, CM, Apr 2001
  $Id: gtienlarge.pro,v 1.3 2001/04/30 16:03:03 craigm Exp $



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