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GTISEG

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
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
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.

## 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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