How do I calculate area enclosed by contour lines?

Question

Kushagra Saxena 2014-6-3

1
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/132216-how-do-i-calculate-area-enclosed-by-contour-lines

评论： S Ch 2021-8-2

采纳的回答： Sara

I have

[x, y, z] = peaks; [C, h] = contour(x, y, z, 20);

Kindly suggest an algorithm or necessary functions to find the area enclosed by, and between, contour lines.

Thanks!

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Sara 2014-6-3

2
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/132216-how-do-i-calculate-area-enclosed-by-contour-lines#answer_139293

在 MATLAB Online 中打开

[x, y, z] = peaks; 
[C, h] = contour(x, y, z, 20);
ch = get(h,'children');
area = zeros(numel(ch),1);
for i = 1:numel(ch)
    x = get(ch(i),'xdata');
    y = get(ch(i),'ydata');
    [x,y] = poly2cw(x,y);
    area(i) = polyarea(x,y);
end

3 个评论
显示 1更早的评论隐藏 1更早的评论

Sara 2014-6-3

It's in the mapping toolbox. It orders the points in a contour in clockwise order, so that the contour is external and an area can be computed (counterclockwise contours are considered internal contours). This is ArcGIS convention and it's followed also by Matlab (not sure who started first). I personally don't have a version working with the basic matlab license and never looked if there is something similar in the file exchange since I have the mapping toolbox.

XING ZHENG 2017-11-7

Dear Sara,

Now I am using your function in the version 2017b: [C, h] = contour(x, y, z, 20); ch = get(h,'children');

However, I can not get 'h' from this sentence. therefore, there is No result of ch. I think this is the difference between the version 2014b and 2017b.

How can I fix this problem? Thanks

Xing

请先登录，再进行评论。

Answer 2

A. Shokouhi 2018-9-19

3
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/132216-how-do-i-calculate-area-enclosed-by-contour-lines#answer_337508

在 MATLAB Online 中打开

I believe some commands in the code provided by Sara is not available in new versions here a code I wrote down that does the same job.

[x, y, z] = peaks;
[C, h] = contour(x, y, z, 5);
n = 0;
i = 1;
sz = size(h.ContourMatrix,2);
nn(1) = h.ContourMatrix(2,1);
xx = h.ContourMatrix(1,2:nn(1)+1);
yy = h.ContourMatrix(2,2:nn(1)+1);
area(1) = polyarea(xx,yy);
while n+nn(i)+i < sz
    n = n + nn(i);
    i = i + 1;
    nn(i)=h.ContourMatrix(2,n+i);
    xx = h.ContourMatrix(1,n+i+1:n+nn(i)+i);
    yy = h.ContourMatrix(2,n+i+1:n+nn(i)+i);
    area(i) = polyarea(xx,yy);
end