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Is there an easy way to get the (x,y) values of a contour line that was plotted like this:
import matplotlib.pyplot as plt
x = [1,2,3,4]
y = [1,2,3,4]
m = [[15,14,13,12],[14,12,10,8],[13,10,7,4],[12,8,4,0]]
cs = plt.contour(x,y,m, [9.5])
plt.show()
607
A contour plot is a graphical technique for representing a 3-dimensional surface by plotting constant z slices, called contours, on a 2-dimensional format. That is, given a value for z, lines are drawn for connecting the (x,y) coordinates where that z value occurs.
If we have a formula for a function z = f(x, y), then we can find the equations for the contours easily. Each contour is obtained by slicing the surface with the horizontal plane z = c, so the equation for the contour at height c is simply f(x, y) = c. (b) f(x, y) = cos√x2 + y2.
Look at the collections property of the returned ContourSet. In particular the get_paths() method of the first collection returns paired points making up each line segment.
cs.collections[0].get_paths()
To get a NumPy array of the coordinates, use the Path.vertices attribute.
p1 = cs.collections[0].get_paths()[0] # grab the 1st path
coor_p1 = p1.vertices
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