PRO do_levels, zmin, zmax, cmin, cmax, nlevels, levels, colors
;this program does levels

dz = ( zmax - zmin ) / FLOAT(nlevels)
levels = FLTARR(nlevels+1)

FOR i_lev = 0, nlevels  DO BEGIN
   levels(i_lev) =  zmin + dz * FLOAT(i_lev)
ENDFOR

dc = ( cmax - cmin ) / FLOAT(nlevels-1)
colors = LONARR(nlevels)
FOR i_lev = 0, nlevels - 1 DO BEGIN
   colors(i_lev) = LONG(cmin + dc * FLOAT(i_lev))
ENDFOR

END