Vector containing the number of colors which will serve to fill contours.
Keywords
NLEVEL
Number of contour to be drawn. By default =20. Active if LABEL=0 or is not specified.
INTERVALLE
Value of an interval betwenn two isolines. By default, it is calculated to
draw 20 isolines. In all cases, this keyword must be returnedt have a nice
caption. If levels do not contain regular intervals, put it at -1.