3 column vector countourf plot error

I have a 3 column vector. I plot a contourf colormap but i have an error as i show below.

Here is my code:

xi=linspace(min(x),max(x),300);
yi=linspace(min(y),max(y),300);
[XI YI]=meshgrid(xi,yi);
ZI = griddata(x,y,z,XI,YI);
figure
contourf(XI,YI,ZI,'edgecolor','none')
colormap(flipud(jet(10)))
shading interp
colorbar
title('X MOMENT','FontSize',14)
grid on
grid minor
hold on;scatter(x,y,'k','filled');
hold off

Plot shape must be as the plan in 2nd pic above. How can i fix this? I dont want to plot the area which i show in the 1st pic.

x and y, point coordinates

z, moment value.

Answer 1

[Riya]

Hi,   

I understand that you want to plot the figure without the triangular region specified in the first image.

For this, you can mask out that region using a custom polygon with “inpolygon” function. This way, you retain full control over which parts of the contour map are visible, ensuring that it matches with your second image.

You can consider updating your code like this:

xi = linspace(min(x), max(x), 300); 
yi = linspace(min(y), max(y), 300); 
[XI, YI] = meshgrid(xi, yi); 

ZI = griddata(x, y, z, XI, YI); 

% Define a polygon to exclude the top-right triangular area 
% This creates a mask that only includes valid plotting region 
polyX = [0 0 12 12 10];  % x-coordinates of the polygon 
polyY = [0 12 12 10 12]; % y-coordinates of the polygon 

% Create mask 
in = inpolygon(XI, YI, polyX, polyY); 
ZI(~in) = NaN;  % Set values outside the polygon to NaN (will not be plotted) 

% Plot the contour 
figure 
contourf(XI, YI, ZI, 'edgecolor', 'none') 
colormap(flipud(jet(10))) 
shading interp 
colorbar 
title('X MOMENT', 'FontSize', 14) 
grid on 
grid minor 
hold on 
scatter(x, y, 'k', 'filled');  
hold off 

• You can adjust “polyX” and “polyY” according to your mesh layout.
• The “inpolygon” function checks whether each point in your interpolation grid lies inside the valid domain.
• Setting ZI(~in) = NaN ensures MATLAB ignores the invalid triangular region during contour plotting.

For more details about inpolygon, you can refer to the following documentation: 

web(fullfile(docroot, 'matlab/ref/inpolygon.html'))