GNUPlot Manual

36 SET-SHOW gnuplot 4.0 59
set cntrparam { { linear
| cubicspline
| bspline
| points
| order
| levels { auto {} |
| discrete {,{,...}}
| incremental , {,}
}
}
}
show contour
This command has two functions. First, it sets the values of z for which contour points are to be
determined (by linear interpolation between data points or function isosamples.) Second, it controls the
way contours are drawn between the points determined to be of equal z. should be an integral
constant expression and , ... any constant expressions. The parameters are:
linear, cubicspline, bspline — Controls type of approximation or interpolation. If linear, then
straight line segments connect points of equal z magnitude. If cubicspline, then piecewise-linear contours
are interpolated between the same equal z points to form somewhat smoother contours, but which
may undulate. If bspline, a guaranteed-smoother curve is drawn, which only approximates the position
of the points of equal-z.
points — Eventually all drawings are done with piecewise-linear strokes. This number controls the
number of line segments used to approximate the bspline or cubicspline curve. Number of cubicspline
or bspline segments (strokes) = points * number of linear segments.
order — Order of the bspline approximation to be used. The bigger this order is, the smoother the
resulting contour. (Of course, higher order bspline curves will move further away from the original
piecewise linear data.) This option is relevant for bspline mode only. Allowed values are integers in the
range from 2 (linear) to 10.
levels — Selection of contour levels, controlled by auto (default), discrete, incremental, and ,
number of contour levels, limited to
MAX_DISCRETE_LEVELS as defined in plot.h (30 is standard.)
For auto, specifies a nominal number of levels; the actual number will be adjusted to give simple
labels. If the surface is bounded by zmin and zmax, contours will be generated at integer multiples of
dz between zmin and zmax, where dz is 1, 2, or 5 times some power of ten (like the step between two
tic marks).
For levels discrete, contours will be generated at z = , ... as specified; the number of
discrete levels sets the number of contour levels. In discrete mode, any set cntrparam levels
are ignored.
For incremental, contours are generated at values of z beginning at and increasing by
, until the number of contours is reached. is used to determine the number of
contour levels, which will be changed by any subsequent set cntrparam levels .
If the command set cntrparam is given without any arguments specified, the defaults are used: linear,
5 points, order 4, 5 auto levels.
Examples:
set cntrparam bspline
set cntrparam points 7
set cntrparam order 10
To select levels automatically, 5 if the level increment criteria are met:
set cntrparam levels auto 5
To specify discrete levels at .1, .37, and .9:
set cntrparam levels discrete .1,1/exp(1),.9