set output "STDOUT", your output may be sent to a le named "STDOUT"! ["May be", not "will be", because some terminals, like x11 or wxt, ignore set output.])

When both set terminal and set output are used together, it is safest to give set terminal rst, because some terminals set a ag which is needed in some operating systems. This would be the case, for example, if the operating system needs to know whether or not a le is to be formatted in order to open it properly.

On machines with popen functions (Unix), output can be piped through a shell command if the rst nonwhitespace character of the lename is 'j'. For instance,

set output "|lpr -Plaser filename" set output "|lp -dlaser filename"

On MSDOS machines, set output "PRN" will direct the output to the default printer. On VMS, output can be sent directly to any spooled device. It is also possible to send the output to DECnet transparent tasks, which allows some exibility.

Parametric

The set parametric command changes the meaning of plot (splot) from normal functions to parametric functions. The command unset parametric restores the plotting style to normal, single-valued expression plotting.

Syntax:

set parametric unset parametric show parametric

For 2D plotting, a parametric function is determined by a pair of parametric functions operating on a parameter. An example of a 2D parametric function would be plot sin(t),cos(t), which draws a circle (if the aspect ratio is set correctly | see set size (p. 144)). gnuplot will display an error message if both functions are not provided for a parametric plot.

For 3D plotting, the surface is described as x=f(u,v), y=g(u,v), z=h(u,v). Therefore a triplet of functions is required. An example of a 3D parametric function would be cos(u)*cos(v),cos(u)*sin(v),sin(u), which draws a sphere. gnuplot will display an error message if all three functions are not provided for a parametric splot.

The total set of possible plots is a superset of the simple f(x) style plots, since the two functions can describe the x and y values to be computed separately. In fact, plots of the type t,f(t) are equivalent to those produced with f(x) because the x values are computed using the identity function. Similarly, 3D plots of the type u,v,f(u,v) are equivalent to f(x,y).

Note that the order the parametric functions are speci ed is xfunction, yfunction (and zfunction) and that each operates over the common parametric domain.

Also, the set parametric function implies a new range of values. Whereas the normal f(x) and f(x,y) style plotting assume an xrange and yrange (and zrange), the parametric mode additionally speci es a trange, urange, and vrange. These ranges may be set directly with set trange, set urange, and set vrange, or by specifying the range on the plot or splot commands. Currently the default range for these parametric variables is [-5:5]. Setting the ranges to something more meaningful is expected.

Plot

The show plot command shows the current plotting command as it results from the last plot and/or splot and possible subsequent replot commands.

In addition, the show plot add2history command adds this current plot command into the history. It is useful if you have used replot to add more curves to the current plot and you want to edit the whole command now.

Pm3d

pm3d is an splot style for drawing palette-mapped 3d and 4d data as color/gray maps and surfaces. It uses an algorithm that allows plotting gridded as well as non-gridded data without preprocessing, even when the data scans do not have the same number of points.

Syntax (the options can be given in any order):

set pm3d {

{at <position> }

{interpolate <steps/points in scan, between scans> }

{scansautomatic | scansforward | scansbackward | depthorder }

{flush { begin | center | end } }

{ftriangles | noftriangles }

{clip1in | clip4in }

{corners2color { mean|geomean|median|min|max|c1|c2|c3|c4 } }

{hidden3d {<linestyle>} | nohidden3d }

{implicit | explicit }

{map }

}

show pm3d unset pm3d

A pm3d color surface is drawn if the splot command speci es with pm3d, if the data or function style is set to pm3d globally, or if the pm3d mode is set pm3d implicit. In the latter two cases, the pm3d surface is draw in addition to the mesh produced by the style speci ed in the plot command. E.g.

splot 'fred.dat' with lines, 'lola.dat' with lines

would draw both a mesh of lines and a pm3d surface for each data set. If the option explicit is on (or implicit is o ) only plots speci ed by the with pm3d attribute are plotted with a pm3d surface, e.g.:

splot 'fred.dat' with lines, 'lola.dat' with pm3d

would plot 'fred.dat' with lines (only) and 'lola.dat' with a pm3d surface.

On gnuplot start-up, the mode is explicit. For historical and compatibility reasons, the commands set pm3d; (i.e. no options) and set pm3d at X ... (i.e. at is the rst option) change the mode to implicit. The command set pm3d; sets other options to their default state.

If you set the default data or function style to pm3d, e.g.:

set style data pm3d

then the options implicit and explicit have no e ect.

Note that when plotting several plots, they are plotted in the order given on the command line. This can be of interest especially for lled surfaces which can overwrite and therefore hide part of earlier plots.

The pm3d coloring can be drawn at any or all of three di erent positions, top, bottom, or surface. See pm3d position (p. 135). The following command draws three color surfaces at di erent altitudes:

set border 4095 set pm3d at s

splot 10*x with pm3d at b, x*x-y*y, x*x+y*y with pm3d at t

See also help for set palette (p. 137), set cbrange (p. 167), set colorbox (p. 104), and de nitely the demo le demo/pm3d.dem.

Algorithm

Let us rst describe how a map/surface is drawn. The input data come from an evaluated function or from an splot data le. Each surface consists of a sequence of separate scans (isolines). The pm3d algorithmlls the region between two neighbouring points in one scan with another two points in the next scan by a gray (or color) according to z-values (or according to an additional 'color' column, see help for using

(p. 83)) of these 4 corners; by default the 4 corner values are averaged, but this can be changed by the option corners2color. In order to get a reasonable surface, the neighbouring scans should not cross and the number of points in the neighbouring scans should not di er too much; of course, the best plot is with scans having same number of points. There are no other requirements (e.g. the data need not be gridded). Another advantage is that the pm3d algorithm does not draw anything outside of the input (measured or calculated) region.

Surface coloring works with the following input data:

1.splot of function or of data le with one or three data columns: The gray/color scale is obtained by mapping the averaged (or corners2color) z-coordinate of the four corners of the above-speci ed quadrangle into the range [min color z,max color z] of zrange or cbrange providing a gray value in the range [0:1]. This value can be used directly as the gray for gray maps. The normalized gray value can be further mapped into a color | see set palette (p. 137) for the complete description.

2.splot of data le with two or four data columns: The gray/color value is obtained by using the last-column coordinate instead of the z-value, thus allowing the color and the z-coordinate be mutually independent. This can be used for 4d data drawing.

Other notes:

1.The term 'scan' referenced above is used more among physicists than the term 'iso curve' referenced in gnuplot documentation and sources. You measure maps recorded one scan after another scan, that's why.

2.The 'gray' or 'color' scale is a linear mapping of a continuous variable onto a smoothly varying palette of colors. The mapping is shown in a rectangle next to the main plot. This documentation refers to this as a "colorbox", and refers to the indexing variable as lying on the colorbox axis. See set colorbox (p. 104), set cbrange (p. 167).

3.To use pm3d coloring to generate a two-dimensional plot rather than a 3D surface, use set view map or set pm3d map.

Position

Color surface can be drawn at the base or top (then it is a gray/color planar map) or at z-coordinates of surface points (gray/color surface). This is de ned by the at option with a string of up to 6 combinations of b, t and s. For instance, at b plots at bottom only, at st plots rstly surface and then top map, while at bstbst will never by seriously used.

Colored quadrangles are plotted one after another. When plotting surfaces (at s), the later quadrangles overlap (overdraw) the previous ones. (Gnuplot is not virtual reality tool to calculate intersections of lled polygon meshes.) You may try to switch between scansforward and scansbackward to force the rst scan of the data to be plotted rst or last. The default is scansautomatic where gnuplot makes a guess about scans order. On the other hand, the depthorder option completely reorders the quadrangles. The rendering is performed after a depth sorting, which allows to visualize even complicated surfaces; see pm3d depthorder (p. 135) for more details.

scansautomaticjscansforwardjscansbackward. These scan options are not in general compatible with hidden-surface removal.

If two successive scans do not have same number of points, then it has to be decided whether to start taking points for quadrangles from the beginning of both scans ( ush begin), from their ends ( ush end) or to center them ( ush center). Note, that ush (centerjend) are incompatible with scansautomatic: if you specify ush center or ush end and scansautomatic is set, it is silently switched to scansforward.

If two subsequent scans do not have the same number of points, the option ftriangles speci es whether color triangles are drawn at the scan tail(s) where there are not enough points in either of the scan. This can be used to draw a smooth map boundary.

Gnuplot does not do true hidden surface removal for solid surfaces, but often it is su cient to render the component quadrangles in order from furthest to closest. This mode may be selected using the options

set pm3d depthorder hidden3d

The depthorder option orders the solid quadrangles; the hidden3d option similarly orders the bounding lines (if drawn). Note that the global option set hidden3d does not a ect pm3d surfaces.

Clipping

Clipping with respect to x, y coordinates of quadrangles can be done in two ways. clip1in: all 4 points of each quadrangle must be de ned and at least 1 point of the quadrangle must lie in the x and y ranges. clip4in: all 4 points of each quadrangle must lie in the x and y ranges.

Color assignment

3 columns of data (x,y,z):

The coloring setup as well as the color box drawing are determined by set palette. There can be only one palette for the current plot. Drawing of several surfaces with di erent palettes can be achieved by multiplot with xed origin and size; don't forget to use set palette maxcolors when your terminal is running out of available colors.

There is a single gray/color value associated to each drawn pm3d quadrangle (no smooth color change among vertices). The value is calculated from z-coordinates from the surrounding corners according to corners2color <option>. The options 'mean' (default), 'geomean' and 'median' produce various kinds of surface color smoothing, while options 'min' and 'max' choose minimal or maximal value, respectively. This may not be desired for pixel images or for maps with sharp and intense peaks, in which case the options 'c1', 'c2', 'c3' or 'c4' can be used instead to assign the quadrangle color based on the z-coordinate of only one corner. Some experimentation may be needed to determine which corner corresponds to 'c1', as the orientation depends on the drawing direction. Because the pm3d algorithm does not extend the colored surface outside the range of the input data points, the 'c<j>' coloring options will result in pixels along two edges of the grid not contributing to the color of any quadrangle. For example, applying the pm3d algorithm to the 4x4 grid of data points in script demo/pm3d.dem (please have a look) produces only (4-1)x(4-1)=9 colored rectangles.

4 columns of data (x,y,z,color):

If a fourth column of data is provided, it is normally interpreted as a separate palette-mapped gray value. The coloring of individual quadrangles works as above, except that the color value is distinct from the z value. As a separate coloring option, the fourth data column may provide instead an RGB color. See rgbcolor variable (p. 35). In this case the plotting command must be

splot ... using 1:2:3:4 with pm3d lc rgb variable

Another drawing algorithm, which would draw quadrangles around a given node by taking corners from averaged (x,y)-coordinates of its surrounding 4 nodes while using node's color, could be implemented in the future. This is already done for drawing images (2D grids) via image and rgbimage styles.

Notice that ranges of z-values and color-values for surfaces are adjustable independently by set zrange, set cbrange, as well as set log for z or cb. Maps can be adjusted by the cb-axis only; see also set view map (p. 156) and set colorbox (p. 104).

Hidden3d

The option set pm3d hidden3d draws the bounding lines of each quadrangle at the same time that the quadrangle itself is drawn. Normally it is used in conjunction with the depthorder option to achieve an approximation to true hidden line removal. This is far more e cient than using the command set hidden3d. The command takes an optional linestyle controlling the appearance of the bounding lines. If the linestyle parameter is negative, or omitted, then the line properties given in the plot command are used. Example of recommended usage: