Matlab: Make a contour plot with 3 vectors

Question

I have 3 data vectors, X (position), Y (position), both of which are not on a regular basis, and Z (value of interest in each place). I tried a path that doesn't work, because it needs a matrix to enter Z.

Answer 1

You can also use griddata .

 %Generate random data x = rand(30,1); y = rand(30,1); z = rand(30,1); %Create regular grid across data space [X,Y] = meshgrid(linspace(min(x),max(x),n), linspace(min(y),max(y),n)) %create contour plot contour(X,Y,griddata(x,y,z,X,Y)) %mark original data points hold on;scatter(x,y,'o');hold off 

Answer 2

For the contour graph, you really need either a matrix of z values ​​or a set (vector) of z values ​​evaluated on a grid. You cannot define contours using isolated Z values ​​at points (X, Y) on the grid (that is, as you say you have).

You need the generation process (or function) to provide values ​​for the grid of points (x, y).

If not, you can create a surface from uneven data , as @nate pointed out correctly, and then draw outlines on that surface.

Consider the following (random) example:

 N = 64; % point set x = -2 + 4*rand(N,1); % random x vector in[-2,2] y = -2 + 4*rand(N,1); % random y vector in[-2,2] % analytic function, or z-vector z = x.*exp(-x.^2-y.^2); % construct the interpolant function F = TriScatteredInterp(x,y,z); t = -2:.25:2; % sample uniformly the surface for matrices (qx, qy, qz) [qx, qy] = meshgrid(t, t); qz = F(qx, qy); contour(qx, qy, qz); hold on; plot(x,y,'bo'); hold off 

The circles correspond to the initial vector points with values (x,y,z) for each point, by the contours on the contours of the interpolation surface.