GNUPlot Manual

36 SET-SHOW gnuplot 4.0 83
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. 60), set cbrange (p. 154).
3. To use pm3d coloring to generate a two-dimensional plot rather than a 3D surface, use set view
map or set pm3d map.
Syntax:
set pm3d
set pm3d {
}
show pm3d
unset pm3d
{ at }
{ scansautomatic | scansforward | scansbackward }
{ flush { begin | center | end } }
{ ftriangles | noftriangles }
{ clip1in | clip4in }
{ corners2color { mean|geomean|median|c1|c2|c3|c4 } }
{ hidden3d | nohidden3d }
{ implicit | explicit }
{ map }
Setting set pm3d (i.e. without options) sets up the default values. Otherwise, the options can be given
in any order.
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 defined 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 firstly 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
filled polygon meshes.) You may try to switch between scansforward and scansbackward to force the
first scan of the data to be plotted first or last. The default is scansautomatic where gnuplot makes a
guess about scans order.
If two subsequent 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 (flush begin), from their ends
(flush end) or to center them (flush center). Note, that flush (center|end) are incompatible with
scansautomatic: if you specify flush center or flush 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 specifies 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.
Clipping with respect to x, y coordinates of quadrangles can be done in two ways. clip1in: all 4 points
of each quadrangle must be defined 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.
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 . The options ’mean’ (default), ’geomean’ and ’median’ produce various
kinds of surface color smoothing. 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