;+
; NAME:
;  rt_cgrid
; PURPOSE: (one line)
;  interpolate a model atmosphere onto evenly spaced pressures 
; DESCRIPTION:
;  interpolate a model atmosphere onto evenly spaced pressures 
; CATEGORY:
;  RT
; CALLING SEQUENCE:
;  rt_cgrid, dat, nz, atm
; INPUTS:
;  dat : body-specific constants
;  nz : number of new atmospheric pressure levels 
; OPTIONAL INPUT PARAMETERS:
; KEYWORD INPUT PARAMETERS:
;  none
; KEYWORD OUTPUT PARAMETERS:
;  none
; OUTPUTS:
;  none
; COMMON BLOCKS:
; SIDE EFFECTS:
; RESTRICTIONS:
;  Modifies atm
; PROCEDURE:
; 
; 
; MODIFICATION HISTORY:
;  Written 2004 May 8, Leslie Young SwRI
;  based on cgrid.f, written by Roger Yelle, 1990
;-

pro rt_cgrid, dat, nz, atm

    gm = dat.gm
    rplnt = dat.rplnt
    pmin = dat.pmin
    pmax = dat.pmax

    dlmin = alog10(pmin)
    dlmax = alog10(pmax)
    dlstep = (dlmax - dlmin) / float(nz - 1)

    ns = 5
    z = dblarr(nz)
    p = dblarr(nz)
    t = dblarr(nz)
    n = dblarr(nz,ns)
    ncol = dblarr(nz,ns)

    logp = (dlmin + findgen(nz)*dlstep )
    p = 10.d^logp
    oldlogp = alog10(atm.p)

    for iz = 0, nz-1 do begin
        if (p[iz] le atm.p[0] ) then begin
            t[iz] = atm.t[0]
            n[iz,*] = atm.n[0,*]*p[iz]/atm.p[0]
            ncol[iz,*] = atm.ncol[0,*]*p[iz]/atm.p[0]
        endif else begin
            t[iz] = rt_fintrp(atm.p,atm.t,p[iz])
            for im = 0, 4 do begin
                 n[iz,im] = rt_fintrp(atm.p,atm.n[*,im],p[iz])
                 ncol[iz,im] = rt_fintrp(atm.p,atm.ncol[*,im],p[iz])
             endfor
            z[iz] = rt_fintrp(oldlogp,atm.z,logp[iz])
        endelse
    endfor

    atm = {  nz:nz, ns:ns,  z:z, p:p, t:t, n:n, ncol:ncol }
    
end