!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!! Copyright 2011 California Institute of Technology
!!!
!!! shift_reference.class
!!!
!!! 2011-05-16 version 1.0 Initial release
!!! 2011-06-03 version 1.1 Copyright notice; use case; no write if no argument
!!! 2014-11-17 version 2.0 sradford
!!!   update for changes in class variable names 
!!!
!!! @shift_reference [ new_restf(MHz) ]
!!!
!!! Shifts reference channel and frequency.
!!!
!!! Use case: You have observed two or more lines simultaneously by doppler-
!!! tracking one of them.  The spectrometer was *centered* at the same line.
!!! Now you want scans *centered* at one of other lines in the signal sideband.
!!! To *center* at one of lines in the image sideband, use the procedure
!!! swap_sideband.class.
!!!
!!! file in ...
!!! file out ...
!!! find ...
!!! set variable spectro write
!!! for i 1 to found
!!! get next
!!! @shift_reference 220398.6765
!!! write
!!! next
!!!
!!! C18O (J=2-1) 219560.3568 MHz
!!! 13CO (J=2-1) 220398.6765 MHz
!!! 12CO (J=2-1) 230538.0000 MHz

!!! NB. Update Class's memory by toggling the units before plotting 
!!! set unit c f
!!! set unit v f 
!!! plot

sic\let clight = 2.99792458e5 /new double ! Speed of light (km/s)

sic\let new_restf = r%head%spe%restf /new double
sic\let new_image = r%head%spe%image /new double
sic\let new_rchan = r%head%spe%rchan /new real
sic\let new_fres = r%head%spe%fres /new real ! No change (topocentric!!!)
sic\let new_vres = r%head%spe%vres /new real

sic\if ("&1 ".ne." ") then
       sic\let new_restf = &1

       sic\let new_image = (r%head%spe%restf+r%head%spe%image)-new_restf
       sic\let new_rchan = r%head%spe%rchan+(new_restf-r%head%spe%restf)*(1+r%head%spe%doppler)/new_fres
       sic\let new_vres = -clight*new_fres/((1+r%head%spe%doppler)*new_restf)

       sic\let r%head%spe%restf = new_restf
       sic\let r%head%spe%image = new_image
       sic\let r%head%spe%rchan = new_rchan
       sic\let r%head%spe%fres = new_fres
       sic\let r%head%spe%vres = new_vres
sic\end if