Python: find contour lines from matplotlib.pyplot.contour()

Question

I\'m trying to find (but not draw!) contour lines for some data:

from pprint import pprint 
import matplotlib.pyplot 
z = [[0.350087, 0.0590954, 0.002165],          


        

Answer 1

It seems that the contour data is in the .allsegs attribute of the QuadContourSet object returned by the plt.contour() function.

The .allseg attribute is a list of all the levels (which can be specified when calling plt.contour(X,Y,Z,V). For each level you get a list of n x 2 NumPy arrays.

plt.figure()
C = plt.contour(X, Y, Z, [0], colors='r')

plt.figure()
for ii, seg in enumerate(C.allsegs[0]):
    plt.plot(seg[:,0], seg[:,1], '.-', label=ii)
plt.legend(fontsize=9, loc='best')

In the above example, only one level is given, so len(C.allsegs) = 1. You get:

contour plot

the extracted curves