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MathGroup Archive 2007

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Contour Lines

  • To: mathgroup at smc.vnet.net
  • Subject: [mg83583] Contour Lines
  • From: Wyn Evans <nwe at ast.cam.ac.uk>
  • Date: Fri, 23 Nov 2007 05:38:41 -0500 (EST)

How do you extract the coordinates of points making up a Contour Line as
a List?

This has been dealt with before in the archive (see e.g., [mg68657])
but the code there seems no longer to work. For example, the following is
suggested

f[x_, y_] := x^2 + 2y^2
plot1 = ContourPlot[f[x, y], {x, -2, 2}, {y, -2, 2}, Contours -> {1},
      ContourShading -> False, PlotPoints -> {30, 30}];
f[x_, y_] := x^2 + 2y^2
plot1 = ContourPlot[f[x, y], {x, -2, 2}, {y, -2, 2}, Contours -> {1},
      ContourShading -> False, PlotPoints -> {30, 30}];

Convert the ContourGraphics to Graphics and then extract the first part
and you will see how Mathematica represents the contours.

contour = First@Graphics@plot1
(output omitted)


I can see that the data I want (the actual coordinates) is there, but I
can't figure how to extract it as a matrix or list.




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