Contour not finding all branches of multi-branch contours

[mgr327]

When a contour consist of several disconnected branches, only one branch is found. The following example illustrates the problem:

using PyPlot, Contour x = -3:0.01:3 y = -3:0.01:3 z = [Float64((xi^2 - yi^2)) for xi in x, yi in y]; h = 2 c = Contour.contour(x, y, z, h); # both Contour and PyPlot have contour() xs, ys = coordinates(c.lines[1]); plot(xs, ys)

The result is one branch, whereas there must be two disconnected ones

The version of Contour from github was used on Julia 0.4.3

versioninfo() Julia Version 0.4.3 Commit a2f713d* (2016-01-12 21:37 UTC) Platform Info: System: Linux (x86_64-redhat-linux) CPU: Intel(R) Core(TM) i7-2600 CPU @ 3.40GHz WORD_SIZE: 64 BLAS: libopenblas (DYNAMIC_ARCH NO_AFFINITY Sandybridge) LAPACK: libopenblasp.so.0 LIBM: libopenlibm LLVM: libLLVM-3.3

[tomasaschan]

As you'll note, length(c.lines) == 2. You'll get the other branch if you do xs2, ys2 = coordinates(c.lines[2]) and plot them too :)

More generally, contour lines will be traced either in loops or reaching the domain boundaries, and each continuous curve will be returned as a separate Curve2 object in c.lines.

Plotting this example again (with Gadfly this time, since I don't have matplotlib on this computer):

x = -3:0.01:3
y = -3:0.01:3
z = [Float64((xi^2 - yi^2)) for xi in x, yi in y];
h = 2

using Contour
c = contour(x,y,z,h)

using Gadfly
plot([layer(x=xs,y=ys,Geom.path) for (xs,ys) in map(coordinates, c.lines)]...)

shows both branches.

(If you want to use Gadfly for plotting, this is built-in there, so you don't have to worry about the Contour package at all if plotting is all you want to do.)

[mgr327]

Thank you!

It is probably going to benefit everyone if you add your example to the readme.md file of the package.