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This command is used to check whether all the spectra in the CLASS
current index are consistent. In particular, checking their spectroscopic
information ensures that their spectral axes are aligned before, e.g.,
averaging the spectra. The consistency status helps CLASS commands or
the end-user to decide whether further processing can be done channel by
channel, or whether resampling is needed to realign the spectra channels.
The spectroscopic consistency aims at checking the alignment of both the
signal frequency and the velocity axes. What should be done with the image
frequency axis is unclear as it depends on the kind of data (e.g., DSB
spectra). One kind of X axes is considered to be aligned when the four
following conditions are fulfilled:
- The left edges of the X ranges covered by the spectra are the same to
a given tolerance;
- The right edges of the X ranges covered by the spectra are the same
to the same tolerance;
- The spectra have the same number of channels;
- The resolution sign is the same.
The tolerance in the two first conditions is set to a fraction of channel
(typically 10%). It is not yet customizable by the user. These two
conditions ensure that the whole X range covered by all the spectra are
identical within the accepted tolerance (including the dilatation due to
the doppler effect that may vary from spectrum to spectrum). Combined with
the third condition, this yields a identical resolution within the accepted
tolerance. In particular, these three conditions tolerate a consistent
shift in the reference channel and physical value at the reference channel.
Finally, the last condition ensures that all the X axes increase or
decrease in the same direction, channelwise. In the CLASS
implementation, the tests 3 and 4 are done first, and only once for all
kind of axes. The conditions 1 and 2 are then applied successively for the
signal frequency and the velocity axes.
Next: The situation at the
Up: CLASS implementation
Previous: The MODIFY REDSHIFT command
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Gildas manager
2015-03-01