ASAP reads the line rest frequency from the RPFITS file when reading the data. The values stored in the RPFITS file are not always correct and so there is a function set_restfreq to set the rest frequencies for the currently selected data.
For each integration, there is a rest-frequency per IF (the rest frequencies are just stored as a list with an index into them). There are a few ways to set the rest frequencies with this function.
If you specify just one rest frequency, then it is set for all IF.
# Set all IFs ASAP>scans.set_restfreqs(freqs=1.667359e9)
If set a rest frequency for each IF, specify a list of frequencies (of length the number of IFs). Regardless of the source, the rest frequency will be set for each IF to the corresponding value in the provided list.
# Set rest frequency for all IFs ASAP>scans.set_restfreqs(freqs=[1.6654018e9,1.667359e9,])
A predetermined ``line catalog'' can be used to set the rest frequency. See section §.