Plot only certain contours

Sirs, I am plotting a contour plot of data

contourf(X,Y,Z)

Say the values of Z range from 0 to 100 (or say, -100 to 100 for another example).

I can overlay the contour values

hold on

[C,h] = contour(X,Y,Z); 

clabel(C,h)

Is it possible to only plot the entire contourf(X,Y,Z) so it is a full contour map

but then only plot the iso-contour lines for particular values?

So, I might want to over-plot only the isocontour that has value 20?

Or, more usefully, say, 20,30 and 40?

kind regards

Answer 1

[Matt J]

From the doc:

contourf(Z,v) draws a filled contour plot of matrix Z with contour lines at the data values specified in the monotonically increasing vector v. To display a single contour line at a particular value, define v as a two-element vector with both elements equal to the desired contour level.

Is this not what you want?

[Matt J]

William White commented:

What I want is a plot that has a filled contour plot (of all values) and a line contour plot of only certain values from the same set of data Z

kind regards W

[Matt J]

I'm still not sure I see the problem. Why not as follows?

contourf(X,Y,Z)

hold on
[C,h] = contour(X,Y,Z,[20,30,40]); 
clabel(C,h)
hold off

[Matt J]

William White commented:

Hi Matt, I think the problem is that I was unaware that the selected values could be inserted like that! thanks a lot, much appreciated! W