# How to get data from contour

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Dmitry Borovoy on 1 Sep 2011
From help:
[X,Y] = meshgrid(-2:.2:2,-2:.2:3);
Z = X.*exp(-X.^2-Y.^2);
[C,h] = contour(X,Y,Z);
set(h,'ShowText','on','TextStep',get(h,'LevelStep')*2)
colormap cool
Now I want to take only levels equal to 0.4
[X,Y] = meshgrid(-2:.2:2,-2:.2:3);
Z = X.*exp(-X.^2-Y.^2);
[C,h] = contour(X,Y,Z);
set(h, 'LevelList', [ 0.4]);
set(h,'ShowText','on','TextStep',get(h,'LevelStep')*2)
colormap cool
And now I want to get data that was displayed at figure and display it with 'plot' function.
figure;plot(C(:,1),C(:,2))
How to get data which I needed?

Friedrich on 1 Sep 2011
EDIT: Code now handles different regions correctly.
Hi,
you can use the contour matrix together with inpolygon to get point inside the region:
For example:
hold on
[X,Y] = meshgrid(-2:.2:2,-2:.2:3);
Z = X.*exp(-X.^2-Y.^2);
[C,h] = contour(X,Y,Z);
set(h, 'LevelList', [ 0.1 0.2 0.3]);
set(h,'ShowText','on','TextStep',get(h,'LevelStep')*2)
colormap cool
x = reshape(X,1,numel(X));
y = reshape(Y,1,numel(Y));
cm = get(h,'ContourMatrix');
index_start = 2;
index_end = cm(2,1)+1;
IN = inpolygon(x,y,cm(1,index_start:index_end),cm(2,index_start:index_end));
for i=2:numel(get(h,'LevelList'))
index_start = index_end + 2;
index_end = index_start + cm(2,index_start-1) - 1;
tmp = inpolygon(x,y,cm(1,index_start:index_end),cm(2,index_start:index_end));
IN = IN | tmp;
end
plot(x(IN),y(IN),'r+');
hold off
figure
hold on
index_start = 2;
index_end = cm(2,1)+1;
plot(cm(1,index_start:index_end),cm(2,index_start:index_end))
for i=2:numel(get(h,'LevelList'))
index_start = index_end + 2;
index_end = index_start + cm(2,index_start-1) - 1;
plot(cm(1,index_start:index_end),cm(2,index_start:index_end))
end
plot(x(IN),y(IN),'r+')
hold off
K E on 15 Aug 2014
Really useful. Should be built in to the contour program or submitted to Fex.

Chad Greene on 15 Aug 2014
C2xyz converts the contour matrix to x,y,z values easily.