XContours
, YContours
, ZContours
Contour lines at constant x values
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XContours , YContours , ZContours  Optional  List of arithmetical expressions 
Objects  Default Values 

plot::Implicit3d 

plot::Cylindrical , plot::Function3d , plot::Spherical , plot::Surface , plot::XRotate , plot::ZRotate 

XContours
, YContours
,
and ZContours
cause contour lines on surface objects
at constant x, y,
or zvalues,
respectively.
By setting these attributes, many surface objects (such as implicit surfaces, function objects etc.) can be instructed to display contour lines.
By setting ZContours = [z_{1},
z_{2}, …]
, contour lines can
be requested at specific places. This is demonstrated in Example 1.
ZContours = [Automatic, n]
causes n contour
lines to be evenly spaced along the range of z values
of the object. Cf. Example 2.
A function plot by default uses height coloring and mesh lines to improve the visual display. With mesh lines disabled, height coloring is often still sufficient:
plotfunc3d(sin(x+cos(0.3*y))*cos(y), XLinesVisible=FALSE, YLinesVisible=FALSE, CameraDirection=[0,0.01,1])
To get a better depth impression, it would help in this example to add contour lines:
plotfunc3d(sin(x+cos(0.3*y))*cos(y), ZContours=[$ 1..1 step 0.25], XLinesVisible=FALSE, YLinesVisible=FALSE, CameraDirection=[0,0.01,1])
In the previous example, we set z values
for the contour lines explicitly. There is an easier way of specifying
equidistant lines, though, by giving the special value Automatic
,
followed by the number of lines to use. For example, implicit surfaces
by default use 15 lines in
each direction of space:
plot(plot::Implicit3d(abs(x)^3+abs(y)^3+abs(z)^3  1, x = 1..1, y=1..1, z=1..1), Axes = None, Scaling = Constrained)
To change the number of lines, we use the syntax outlined above:
plot(plot::Implicit3d(abs(x)^3+abs(y)^3+abs(z)^3  1, x = 1..1, y=1..1, z=1..1, XContours = [Automatic, 4], YContours = [Automatic, 11], ZContours = [Automatic, 21]), Axes = None, Scaling = Constrained)
Note that two of the lines are at the extremal values and therefore usually not visible.
Contour lines are drawn using the same settings for LineWidth
and LineColor
as
parameter lines are. In the following example, we use a modified copy
of a function object that only displays contour
lines, but with settings different from the function object proper.
f := plot::Function3d(x^2  2*x*y  y^2, x = 2..2, y = 2..2): plot(f, plot::modify(f, ZContours = [Automatic, 15], LineWidth = 1, LineColor = RGB::Gray30.[0.8], XLinesVisible = FALSE, YLinesVisible = FALSE, Filled = FALSE))
By using a transformation that maps space into a plane, we can use this technique (by setting some more options) to display heightcolored contour lines below a function plot:
f := plot::Function3d(8*sin(xcos(y))+(x^2+x*y), x = 3..3, y = 3..3, Submesh=[2,2]): plot(f, plot::Transform3d([0, 0, 9], [1, 0, 0, 0, 1, 0, 0, 0, 0], plot::modify(f, ZContours = [Automatic, 15], LineWidth = 0.5, LineColorType = Dichromatic, LineColor = RGB::Red, LineColor2 = RGB::CornflowerBlue, XLinesVisible = FALSE, YLinesVisible = FALSE, Filled = FALSE)))