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The CONSISTENCY command

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:

  1. The left edges of the X ranges covered by the spectra are the same to a given tolerance;
  2. The right edges of the X ranges covered by the spectra are the same to the same tolerance;
  3. The spectra have the same number of channels;
  4. 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 up previous contents
Next: The situation at the Up: CLASS implementation Previous: The MODIFY REDSHIFT command   Contents
Gildas manager 2015-03-01