vertices in contour matrix

Question

strunack 2013-4-8

0
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https://ww2.mathworks.cn/matlabcentral/answers/70988-vertices-in-contour-matrix

回答： Chad Greene 2014-5-22

Dear Friends, I need a help regarding contour plot. I plot contour(X,Y,Z,20). Depending on level value, some contours are closed circles and some are not. Close circles starts usually starts from lowest value (typical 0.001). As level increases with fine step, at some particular value circle becomes open with various other patterns. My task is to identify the largest level for a closed circle.

I tried with

[c, h]=contour(R,Z,F,[i]);

i being step index in for loop. Initially I thought I will retrieve the individual plots and check for closeness. But I find the position of vertices are quite random.

My questions are

1. Is there a way to find vertices value and index position in c matrix. 2. Do you suggest a any other better way for identifying last closed circle.

With thanks