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LAS\EXTRACT [X1 X2 [Unit]] [/INDEX]
In its default mode, EXTRACT copies R into T, extracts a subsection of
R, and save the result in R. If the option /INDEX is present, or if SET
ACTION is INDEX, a subsection of each observation in the index is ex-
tracted and saved in the output file.
Without arguments, the cursor is invoked (if available) to define the
subsection range. If the arguments X1 and X2 are present, the subsection
is defined by this range, in the given Unit (if any) or by default in
the current X axis unit (SET UNIT). X2 can be indifferently greater or
lower than X1, and Unit is a single character in the four C)hannel,
V)elocity, F)requency or I)mage. Note that if Unit is F or I, the number
of extracted channels can vary for two similar observations (same setup)
because of different Doppler factors.
If the range overlaps the input spectrum limits, a warning is raised and
the missing data is filled with the blanking value. Requesting a range
off the input spectrum is an error. The command FIND /FREQUENCY can help
you to build an index with spectra overlapping one frequency or one
range of frequencies.
On return, the observation header is consistently updated: the reference
channel is shifted and number of channels updated. The PLOT section
(which remembers the previous plotting limits) is disabled because it
probably does not makes sense for the extracted data array.
Only regularly sampled X axes are supported.