Scattered 3d data to contourf plot

Hi,

I think this is a trivial question for more experienced users. I searched in the file exchange webpage, but still I cannot figure out a solution for my problem (or maybe I was not able to understand the provided files).

I have a X,Y and Z variables. The values for these 1x200 vectors were acquired on the lab. In order to assess their organization I did: scatter3(X,Y,X)

However, this type of plot is quite hard to understand or to see any kind of trend. So, I thought that I should plot this data using contourf.

Although, if I code contourf(X,Y,Z), regarding the shown error mensage I do understand that the data input demanded for contourf are not the same for scatter3.

Summing up, how I can run contourf(X,Y,Z)?

Best So,

Answer 1

[Samayochita]

Hi Tiago,

Here are my observations:

• There is a difference in the syntax of scatter3() and contourf(). In “scatter3(X, Y, Z)” (https://in.mathworks.com/help/matlab/ref/scatter3.html) X, Y and Z are arrays of the same size that represent coordinates in a three-dimensional space whereas in “contourf(X, Y, Z)” (https://www.mathworks.com/help/matlab/ref/contourf.html) X and Y are matrices specifying the grid of points, and Z is a matrix of values corresponding to those points.
• For “contourf,” you need to create a 2D grid of values for X and Y and then assign the corresponding Z values to the grid. You can achieve this by using the “meshgrid” (https://www.mathworks.com/help/matlab/ref/meshgrid.html) to create a grid for X and Y and then interpolate the Z values onto this grid. Here is an example code for your reference:

% Assuming X, Y, and Z are your 1x200 vectors. 
X = rand(1, 200);  
Y = rand(1, 200);  
Z = rand(1, 200); 

% Create a meshgrid for X and Y 
[Xgrid, Ygrid] = meshgrid(linspace(min(X), max(X), 50), linspace(min(Y), max(Y), 50)); 

% Interpolate Z values for the grid 
Zgrid = griddata(X, Y, Z, Xgrid, Ygrid, 'cubic');  % the interpolation method can be 'linear', 'cubic', or 'nearest' 
% Plot the contourf 
contourf(Xgrid, Ygrid, Zgrid, 20);  % Here '20' is the number of contour levels 
colorbar; 
xlabel('X'); 
ylabel('Y'); 
title('Contourf plot of Z'); 

Hope this helps!

Answer 2

[Mathieu NOE]

hello

first alternative is :

% create somme dummy data
N = 20;
z = peaks(N);

% convert to scatter points
z = z(:);
x = rand(size(z));
y = rand(size(z));

% main code
F = scatteredInterpolant(x, y, z);
xv = linspace(min(x), max(x), 100);
yv = linspace(min(y), max(y), 100);
[X,Y] = meshgrid(xv, yv);
Z = F(X, Y);

% plot
figure
contour(X, Y, Z)
grid
xlabel('X')
ylabel('Y')
zlabel('Z')
colorbar('vert')
colormap('jet')

●

[Mathieu NOE]

second option is :

Contour Plot for Scattered Data - File Exchange - MATLAB Central