When there are multiple spectral windows, it is often convenient to be able
to select based on the spectral window, rather than a channel range. This is
select=window, which selects data from a set of
spectral windows. The general form is
select=window(w1,w2,...)where w1, w2, etc, are spectral window numbers. For example, selecting the data from spectral windows 1, 2 and 3 would be achieved with
Spectral window selection and velocity/felocity linetypes are quite complementary. The different spectral windows might correspond to different spectral lines with different rest frequencies, and so it is desirable to select only a subset of spectral windows (those corresponding to a given spectral line) in forming the output velocity channels.
Spectral window selection is not particularly complementary to
channel linetype processing - both select a range of input channels.
When line=channel and select=window are used together, the
total apparent number of input channels is equal to the number of channels
in the selected spectral windows, and the start channel number of the
line parameter is relative to the first selected spectral
window. For example, if there are multiple spectral windows, then
would select just the first channel of the second spectral window. Similarly
select=window(2)would select 10 channels, being every second channel starting at the 8th channel of the second spectral window.
There are some restrictions on the use of spectral window selection.
select=time(0:00,1:00),window(1,2),or time(0:00,2:00),window(3,4)Here data in the times 0:00 to 1:00 could have been selected by either of the two clauses. There is no guarantee as to which of the two window subcommands will be used during this time interval.