Highlight a specific contour level in contour plot?

Hi,

I have a contour plot and I want to highlight only a selected contour level. How can I do it? I tried all techniques reported but no success.

my code is follows and I want to highlight contour only with levels equal to 0 (zero). Can anyone help me out. Thank you. I am using matlab2015a.

z=load('data.txt');z=round(z);
x=1:0.1:9.1;
y=80:0.5:115;
[C,h] = contourf(x,y,x);
colorbar;
thisH = findall(h,'Userdata',0.0);
set(thisH,'linewidth',5)

Answer 1

[Bjorn Gustavsson]

The simplest way might just be to add an separate contour:

[C,h] = contourf(peaks(123));
hold on
emphasis_level = 0;
contour(peaks(123),[1 1]*emphasis_level,'k','linewidth',2);

HTH

[Madan Kumar]

Thank you

[Madan Kumar]

Sorry, I thought it worked but when I tried with a simple example it didn't. for example, I want to highlight levels with zeros. here is the code.

M=[1 2 3;4 5 6;0 0 0;1 1 1; 2 2 2;0 1 0];
X=1:3;Y=1:6;
[c,h]=contourf(X,Y,M);
hold on;
emphasis_level = 0;
contour(X,Y,M,[1 1]*emphasis_level,'r','linewidth',1.5);

[Bjorn Gustavsson]

That is because you will get no contours at zero in your example, that is another problem more related to the contouring-algorithm and intensities at the extrema of the data range. If you try:

M=[1 2 3;4 5 6;0 0 0;1 1 1; 2 2 2;0 1 0];
X=1:3;Y=1:6;
[c,h]=contourf(X,Y,M-1);
hold on;
emphasis_level = 0;
contour(X,Y,M-1,[1 1]*emphasis_level,'r','linewidth',1.5);

[Madan Kumar]

Okay..I checked the data manually and, to me, it feels like the first code (your first response) is taking values less than or equal to zeros in the contour plot. Becasue I am getting the areas with red boundaries at some regions with non-zero values (but with negative values). Or is it problem with the number of contour levels?

[Bjorn Gustavsson]

Yes. In my first example peaks has values safely above and below zero. In your example M has extreme-values exactly at zero. Then you will just not get a contour at that level, it might be a requirement that M has values above and below a contour-level to actually make a contour, think about this the way of a topographic map, for a contour to be meaningfull the topography has to be above that level on one side and lower on the other. My interpretation is that the reason you get no contour just at zero in your example is an unrelated problem to the highlighting question.

[Madan Kumar]

got it..thank u..