Marker on contourf plot

Dear all,

I have plotted a contour plot using contourf using Z2. I would like to add markers at certain values in Z2, these values are in LS1 and LS2. But instead of plotting the marker directly on top of the contour plot, I get something like the image:

load('Test.mat');

contourf(Z2,20,'edgecolor','none');
hold on;
plot(LS1,'b+','MarkerSize',5);
hold on;
plot(LS2,'rx','MarkerSize',5);
colorbar;

Does anyone have any idea on the issue? Thank you very much!

Answer 1

[Voss]

When calling contourf with syntax contourf(Z) (i.e., no X and Y), then the x- and y-coordinates of the contour plot are taken to be the column and row indices, respectively, of the matrix Z. That is to say, x is 1:size(Z,2) and y is 1:size(Z,1). (Your Z2 is of size 23-by-23, so your contour goes from x = 1 to x = 23 and y = 1 to y = 23.)

The matrices LS1 and LS2 contain mostly NaNs, and the non-NaN elements are identical to the elements in the corresponding positions in Z2. I figure you want to plot the points where LS1 and LS2 are non-NaN with their respective markers on top of the contour. To do that, you can use find with two outputs (rows and columns), as that will give you the locations consistent with your contour plot.

load Test

contourf(Z2,20,'edgecolor','none');
colormap(jet())
colorbar
hold on

[r1,c1] = find(~isnan(LS1));
[r2,c2] = find(~isnan(LS2));

plot(c1,r1,'b+','MarkerSize',5);
plot(c2,r2,'rx','MarkerSize',5);

[Eli]

Thank you for the detailed explanation!

[Voss]

You're welcome!

Answer 2

[Akira Agata]

Please use (x,y) coordinate for plotting markers.

The following is an example:

load('Test.mat');

% Find (x,y) coordinate of values
[row1, col1] = find(~isnan(LS1));
[row2, col2] = find(~isnan(LS2));

% Visualize the result
figure
contourf(Z2, 20, "EdgeColor", "none");
hold on
scatter(col1, row1, "b+")
scatter(col2, row2, "rx")
colorbar;

[Eli]

Thank you!