pro spshft,ds,spi,a=a


; Shift an image so that the wavelength solution is
; the same for all columns


if n_params() lt 1  then begin

        print,'pro spshft,ds,spi,a'
        return
endif
 



if (keyword_set(a) eq 0) then  a=[116.456,-8.52431e-05] ;row shift

sz=size(ds) 
nrow=sz(2)
ncol=sz(1)

if (sz(0) eq 2 ) then begin

   spi = fltarr(ncol,nrow)
   p = findgen(ncol)

   for i=0,nrow-1 do begin

      spi(*,i) = interpolate(ds(*,i),p+a(1)*(i-a(0))^2.0,/cubic)

   endfor

endif else begin

   nim = sz(3)
   spi = fltarr(ncol,nrow,nim)
   p = findgen(ncol)


   for j=0,nim-1 do begin

      for i=0,nrow-1 do begin

         spi(*,i,j) = interpolate(ds(*,i,j),p+a(1)*(i-a(0))^2.0,/cubic)

      endfor
   endfor


endelse

return
end