Need help creating a plot with x,y,z (2d plot with contour)

Hi! I need help creating a plot. I am given x,y, and z data points. I need to plot x and y and contour the z points. I've provided the code I created, although not sure if im on the right track or not. I have also attached a plot of what the plot should look similar to.

clear all; close all; clc

%knownn info
x = [0 13 48 56 101 208 255 297 321 342 451 541 567 599 605 632 675 700 710 750];
y = [123 540 22 321 111 679 314 220 543 119 440 256 12 431 337 709 229 109 334 402];
z = [130.64 131.99 130.58 131.66 131.28 133.31 132.71 132.36 133.36 132.28 134.04 134.09 133.24 134.53 134.57 135.73 134.40 134.02 135.79 135.20];

xv = linspace(min(x),max(x),numel(x));
yv = linspace(min(y),max(y),numel(y));
[Xm,Ym] = ngrid(xv, yv);
Zm = griddata (x,y,z,Xm,Ym);

figure
contourf(Xm,Ym,Zm)
grid

[Muh Alam]

Z coordinates( in your code Zm) must be matrix 2x2 at least. it is vector in the code you gave.

[Mackenzie Weeks]

yes, but how would I go about that?

Answer 1

[Cris LaPierre]

You have to do some interpolation to create a contour plot from your data. When plotting, you must have gridded data, meaning all your z values in a column must be for the same x value, and your row values must be for the same y value. I would suggest using scatteredinterpolant.

%knownn info
x = [0 13 48 56 101 208 255 297 321 342 451 541 567 599 605 632 675 700 710 750];
y = [123 540 22 321 111 679 314 220 543 119 440 256 12 431 337 709 229 109 334 402];
z = [130.64 131.99 130.58 131.66 131.28 133.31 132.71 132.36 133.36 132.28 134.04 134.09 133.24 134.53 134.57 135.73 134.40 134.02 135.79 135.20];

% Create a scattered interpolant for the existing data
F=scatteredInterpolant(x',y',z',"linear","linear");

% Now create regularly spaced x and y values
xq = linspace(min(x),max(x),50);
yq = linspace(min(y),max(y),50);
[Xq,Yq] = meshgrid(xq,yq);
% Use the meshgrid of x and y to compute your grid of z values
Zq = F(Xq,Yq);

contourf(Xq,Yq,Zq)

Just be aware that your interpolation is an approximation based on the data you have. The more data, the better.

[Mackenzie Weeks]

thanks so much! how would you go about labeling the z coordinates?

[Cris LaPierre]

You can use the ShowText name-value pair in contourf.

%knownn info
x = [0 13 48 56 101 208 255 297 321 342 451 541 567 599 605 632 675 700 710 750];
y = [123 540 22 321 111 679 314 220 543 119 440 256 12 431 337 709 229 109 334 402];
z = [130.64 131.99 130.58 131.66 131.28 133.31 132.71 132.36 133.36 132.28 134.04 134.09 133.24 134.53 134.57 135.73 134.40 134.02 135.79 135.20];

% Create a scattered interpolant for the existing data
F=scatteredInterpolant(x',y',z',"linear","linear");

% Now create regularly spaced x and y values
xq = linspace(min(x),max(x),50);
yq = linspace(min(y),max(y),50);
[Xq,Yq] = meshgrid(xq,yq);
% Use the meshgrid of x and y to compute your grid of z values
Zq = F(Xq,Yq);

contourf(Xq,Yq,Zq,'ShowText',true)

You can also use the clabel function.

[Mackenzie Weeks]

thanks so much!