GNUPlot Manual

70 gnuplot 4.0 36 SET-SHOW
For this to be possible, the surface needs to have ’grid structure’ (see splot datafile (p. 155) about
this), and it has to be drawn with lines or with linespoints.
When hidden3d is set, both the hidden portion of the surface and possibly its contours drawn on the
base (see set contour (p. 61)) as well as the grid will be hidden. Each surface has its hidden parts
removed with respect to itself and to other surfaces, if more than one surface is plotted. Contours
drawn on the surface (set contour surface) don’t work. Labels and arrows are always visible and are
unaffected. The key is also never hidden by the surface.
Functions are evaluated at isoline intersections. The algorithm interpolates linearly between function
points or data points when determining the visible line segments. This means that the appearance of a
function may be different when plotted with hidden3d than when plotted with nohidden3d because
in the latter case functions are evaluated at each sample. Please see set samples (p. 90) and set
isosamples (p. 71) for discussion of the difference.
The algorithm used to remove the hidden parts of the surfaces has some additional features controllable
by this command. Specifying defaults will set them all to their default settings, as detailed below.
If defaults is not given, only explicitly specified options will be influenced: all others will keep their
previous values, so you can turn on/off hidden line removal via set {no}hidden3d, without modifying
the set of options you chose.
The first option, offset, influences the linestyle used for lines on the ’back’ side. Normally, they are
drawn in a linestyle one index number higher than the one used for the front, to make the two sides of
the surface distinguishable. You can specify a different line style offset to add instead of the default 1,
by offset . Option nooffset stands for offset 0, making the two sides of the surface use the
same linestyle.
Next comes the option trianglepattern . must be a number between 0
and 7, interpreted as a bit pattern. Each bit determines the visibility of one edge of the triangles each
surface is split up into. Bit 0 is for the ’horizontal’ edges of the grid, Bit 1 for the ’vertical’ ones, and
Bit 2 for the diagonals that split each cell of the original grid into two triangles. The default pattern is
3, making all horizontal and vertical lines visible, but not the diagonals. You may want to choose 7 to
see those diagonals as well.
The undefined option lets you decide what the algorithm is to do with data points that are
undefined (missing data, or undefined function values), or exceed the given x-, y- or z-ranges. Such points
can either be plotted nevertheless, or taken out of the input data set. All surface elements touching a
point that is taken out will be taken out as well, thus creating a hole in the surface. If = 3,
equivalent to option noundefined, no points will be thrown away at all. This may produce all kinds of
problems elsewhere, so you should avoid this. = 2 will throw away undefined points, but keep
the out-of-range ones. = 1, the default, will get rid of out-of-range points as well.
By specifying noaltdiagonal, you can override the default handling of a special case can occur if
undefined is active (i.e. is not 3). Each cell of the grid-structured input surface will be divided
in two triangles along one of its diagonals. Normally, all these diagonals have the same orientation relative
to the grid. If exactly one of the four cell corners is excluded by the undefined handler, and this is
on the usual diagonal, both triangles will be excluded. However if the default setting of altdiagonal
is active, the other diagonal will be chosen for this cell instead, minimizing the size of the hole in the
surface.
The bentover option controls what happens to another special case, this time in conjunction with the
trianglepattern. For rather crumply surfaces, it can happen that the two triangles a surface cell is
divided into are seen from opposite sides (i.e. the original quadrangle is ’bent over’), as illustrated in
the following ASCII art:
C----B
original quadrangle: A--B displayed quadrangle: |\ |
("set view 0,0") | /| ("set view 75,75" perhaps) | \ |
|/ | | \ |
C--D | \|
A D
If the diagonal edges of the surface cells aren’t generally made visible by bit 2 of the there,