Create contour plot from scatter plot

Question

mads skibsted 2024-4-23

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2110711-create-contour-plot-from-scatter-plot

评论： Mathieu NOE 2024-4-24

k.txt

I want to create a contour from this matrix with x,y and z data. x is the length, y is the width and z is the deviatoric strain.

I want to create a contour plot instead. Is that possible?

figure; hold on ; box on 
scatter(x,y,[20],-z,'filled')
ylabel('Width, \ $(\mathrm{m})$','FontSize',15); xlabel('Length, \ $(\mathrm{m})$','FontSize',15,'FontName','times')

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Answer 1

Voss 2024-4-23

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2110711-create-contour-plot-from-scatter-plot#answer_1446526

在 MATLAB Online 中打开

k.txt

M = readmatrix('k.txt');

x = M(:,1);

y = M(:,2);

z = M(:,3);

I = scatteredInterpolant(x,y,z);

Warning: Duplicate data points have been detected and removed - corresponding values have been averaged.

N = 80;

X = linspace(min(x),max(x),N);

Y = linspace(min(y),max(y),N);

[X,Y] = meshgrid(X,Y);

Z = I(X,Y);

contour(X,Y,Z)

colorbar

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Mathieu NOE 2024-4-24

在 MATLAB Online 中打开

k.txt

some minor improvements (??) like the log spaced v (levels) + automatic minimum radius computation for the inner hole

M = readmatrix('k.txt');

x = M(:,1);

y = M(:,2);

z = M(:,3);

%% uncomment the code below if you want to overlay the scatter and the ontour plot

% figure;

% hold on ;

% box on

% scatter(x,y,[20],z,'filled')

% colormap('jet');

% colorbar('vert');

% ylabel('Width, \ $(\mathrm{m})$','FontSize',15);

% xlabel('Length, \ $(\mathrm{m})$','FontSize',15,'FontName','times')

% axis square

%%%%%%

% v = linspace(min(z),max(z),50); % define the levels for the contour plot

v = logspace(log10(min(z)),log10(max(z)),50);

I = scatteredInterpolant(x,y,z,'linear','none');

Warning: Duplicate data points have been detected and removed - corresponding values have been averaged.

N = 100;

X = linspace(min(x),max(x),N);

Y = linspace(min(y),max(y),N);

[X,Y] = meshgrid(X,Y);

[th,r] = cart2pol(x,y);

idx = X.^2+Y.^2 <= (ceil(min(r)))^2;

X(idx) = NaN;

Y(idx) = NaN;

Z = I(X,Y);

[c,h] = contour(X,Y,Z,v);

colormap('jet');

grid on

axis square

% clabel(c,h,v,'LabelSpacing',3000,'Color','b','FontWeight','bold')

colorbar('vert')

Voss 2024-4-24

Those are definitely improvements. Thank you!

Mathieu NOE 2024-4-24

hello @Voss

tx for the nice comment :)

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Answer 2

Mathieu NOE 2024-4-23

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2110711-create-contour-plot-from-scatter-plot#answer_1446521

在 MATLAB Online 中打开

k.txt

hello

sure you can do that

notice that I needed to create lot of levels to display the outer contour line because your z data is highly concentrated in the lower portion of the range (we can see that by plotting a histogram)

data = readmatrix('k.txt');

x = data(:,1);

y = data(:,2);

z = data(:,3);

histogram(z,200)

% Interpolate the scattered data

xd = linspace(min(x),max(x),100);

yd = linspace(min(y),max(y),100);

v = linspace(min(z),max(z),200); % define the levels for the contour plot

[xq,yq] = meshgrid(xd,yd);

zq = griddata(x,y,z,xq,yq);

Warning: Duplicate data points have been detected and removed - corresponding values have been averaged.

% replace NaN's generated by griddate with 0 (or a value lower than min(z)

zq(isnan(zq)) = 0;

% contour plot

[c,h] = contour(xq,yq,zq,v);

grid on

axis square

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Mathieu NOE 2024-4-23

在 MATLAB Online 中打开

k.txt

this could be an alternative , with less contour lines

now the levels are generated with a log scale

and I use clabel to show what are the corresponding z value

data = readmatrix('k.txt');

x = data(:,1);

y = data(:,2);

z = data(:,3);

% Interpolate the scattered data

xd = linspace(min(x),max(x),100);

yd = linspace(min(y),max(y),100);

% v = linspace(min(z),max(z),200); % define the levels for the contour plot

v = logspace(log10(min(z)),log10(max(z)),10);

[xq,yq] = meshgrid(xd,yd);

zq = griddata(x,y,z,xq,yq);

Warning: Duplicate data points have been detected and removed - corresponding values have been averaged.

% replace NaN's generated by griddate with 0 (or a value lower than min(z)

zq(isnan(zq)) = 0;

% contour plot

[c,h] = contour(xq,yq,zq,v);

grid on

axis square

clabel(c,h,v,'LabelSpacing',3000,'Color','b','FontWeight','bold')

colorbar('vert')

mads skibsted 2024-4-23

Hi, Thanks,

But it is reallt import to keep the hole in the middle. There is no contours at that area..

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Answer 3

Walter Roberson 2024-4-23

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2110711-create-contour-plot-from-scatter-plot#answer_1446601

See https://www.mathworks.com/matlabcentral/fileexchange/38858-contour-plot-for-scattered-data

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Mathieu NOE 2024-4-24

在 MATLAB Online 中打开

It works on my side but with tricontour I don't know how you can manage to keep the inner hole

data = readmatrix('k.txt');
x = data(:,1);
y = data(:,2);
z = data(:,3);
% v = linspace(min(z),max(z),20); % define the levels for the contour plot
v = logspace(log10(min(z)),log10(max(z)),50);
tri=delaunay(x,y);           % triangulate scattered data
[C,h]=tricontour(tri,x,y,z,v);
% clabel(C,h)
colormap('jet');
grid on
axis square
% clabel(c,h,v,'LabelSpacing',3000,'Color','b','FontWeight','bold')
colorbar('vert')