; =================================================================
function filename_3d,hem,year,version,revision,tag_preliminary
; =================================================================
    ; This function constructs the CV (3d) file name given the 
    ; following input:
    ;
    ;          hem    hemisphere ('north' or 'south')        string
    ;         year    year (e.g. '2009')                     string
    ;      version    CIPS data version # (e.g., '05.20')    string
    ;     revision    CIPS data revision # (e.g., '05')      string
    ; -----------------------------------------------------------------

    y1=strmid(strtrim(year,2),2,2)
    y2=strmid(strtrim(year+1,2),2,2)

    if(hem eq 'south') then season=hem+'_'+y1+y2 else season=hem+'_'+y1

    if (tag_preliminary) then $
       file='cips_3d_'+season+'_v'+version+'_r'+revision+'.preliminary.txt' $
    else $
       file='cips_3d_'+season+'_v'+version+'_r'+revision+'.txt'

    return,file
end