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GAPNAN

GAPNAN

Name


  GAPNAN

Author


  Craig B. Markwardt, NASA/GSFC Code 661, Greenbelt, MD 20770
  Craig.Markwardt@nasa.gov

Purpose


  Insert NANs in time series gaps to facilitate plotting

Major Topics


  Time series

Calling Sequence


  GAPNAN, TT, Y1, [Y2,] [Y3,] [Y4,] [Y5], MAXGAP=, GTI=

Description


  This procedure is an covenience procedure for plotting time series
  which may have gaps. In other words, a time series where there
  will be time segments of data, and periods of no data which are
  considered "gaps." Sometimes it is desireable to plot the data
  with lines connecting the data, but no lines across gaps.
  GAPNAN will insert NAN values in time series between gaps.
  Because an IDL line plot will not connect points with NAN values
  between them, inserting a NAN value is an effective way of
  suppressing connecting lines between gaps.
  The user can specify gaps in one of two ways, using either the
  MAXGAP or the GTI keyword. The user must specify one of these
  keywords, but not both.
  The user can specify the maximum allowable gap size between time
  series samples using the MAXGAP keyword. If the time step between
  samples is larger than MAXGAP then a gap is declared. (This
  functionality uses the Markwardt library routine GTISEG.)
  The GTI keyword explicitly designates "good" time intervals. The
  user should pass a 2xn array using the GTI keyword, which indicate
  the start/stop time of each good-time. If the time samples cross
  between good time intervals (or if a time sample is noth within a
  good interval at all), then a gap is declared. (This
  functionality uses the Markwardt library routine GTIWHERE.)
  The values Y1, Y2, etc. are the dependent variables. Up to five
  dependent variables can be adjusted in one call.

Inputs


  TIME - time variable, used to find gaps. Upon return, TIME will
          be modified in-place. Whereever gaps occur, a new time
          value will be inserted with the value of NAN.

Optional Inputs


  Y1, Y2, Y3, Y4, Y5 - the optional dependent variable. Must have
          the same number of elements as TIME. Wherever NANs were
          inserted in the TIME array, NANs will also be inserted at
          the corresponding positions of Y1, Y2, etc. Upon return,
          these parameters will be modified in-place. The user may
          pass up to five dependent variables in one call.
 

Input Keyword Parameters


  MAXGAP - maximum gap size between segments, in the same units as
            the TIME variable. The user must specify either MAXGAP
            or GTI, but not both.
  GTI - a 2xN array, in the same units as the TIME variable,
        indicating "good" time intervals. The user must specify
        either MAXGAP or GTI, but not both.

Example


  ;; Sample data with gap between 3 and 10
  tt = [1,2,3, 10, 11, 12d]
  yy = [1,1,1, 2, 2, 2d ]
  gapnan, tt, yy maxgap=5
  ;; Note that a NaN is inserted between 3 and 10, since the actual gap of
  ;; 7 is larger than the maximum of 5.
  ;; Sample data with gap between 3 and 10
  tt = [1,2,3, 10, 11, 12d]
  yy = [1,1,1, 2, 2, 2d ]
  ;; Good times from 0.5-2.5 and 10.5-13.0
  gti = [[0.5,2.5], [10.5,13]]
  gapnan, tt, yy, gti=gti
  ;; Note that a Nan is inserted between 2 and 3 because the good
  ;; interval stops at 2.5; a Nan is inserted between 3 and 10, and
  ;; 10 and 11 because neither 3 nor 10 are within a good interval.

Modification History


  Written and documented, 2010-04-27 CM
  Added MAXGAP and GTI keywords, 2010-11-13 CM
  Square bracket array notation, 2011-12-21 CM
  Bug fix for more than one input array (was ignored), 2012-02-20 CM
  Bug fix when input GTI is set; defend against array bounds error;
    add USAGE message, 2013-03-16 CM



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