MATLAB: How to create a surface plot with 3 independent variables? I dont want to construct using a trisurface plot. File is attached.

meshmeshgridsurf

I would like to construct a 3D (surface plot) to show graphical representation of mode shape. X and Y denote the scan point and magnitude represents the displacement at that point. For example magnitude1 (m1) represents the displacement at point (x1,y1). Please advise.

Best Answer

Your data are gridded, so you simply need to reshape the vectors appropriately, then plot the resulting matrices:

fidi = fopen('fastscan 118hz 1g.txt','rt');
Dc = textscan(fidi, '%f%f%f', 'HeaderLines',11, 'CollectOutput',1);
fclose(fidi);
D = cell2mat(Dc);
[~,frames] = unique(D(:,2));                                            % Indices Of Repeat Values
mdf = mean(diff(frames));                                               % Frame Length
Xr = reshape(D(:,1), mdf, []);                                          % Reshape ‘X’
Yr = reshape(D(:,2), mdf, []);                                          % Reshape ‘Y’
Mr = reshape(D(:,3), mdf, []);                                          % Reshape ‘Magnitude’
figure
surfc(Xr, Yr, Mr)
grid on
view(105, 15)
xlabel('X')
ylabel('Y')
zlabel('Magnitude (m)')

producing:

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MATLAB: How to get 2d line of surface plot section view

Try this:

[X,Y,Z] = peaks(50);                                            % Create Surface Data
figure
surf(X,Y,Z)
grid on
xlabel('X')
ylabel('Y')
zlabel('Z')
title('Surface Plot')
Xval = 0.5;
Yp = interp1(X(1,:), Y.', Xval);
Zp = interp1(X(1,:), Z, Xval);
figure
plot(Yp, Zp, '-r')
grid
xlabel('Y')
ylabel('Z')
title(sprintf('Slice Through Surface At X = %.3f', Xval))

Since the ‘X’ value you want may not correspond to an existing ‘X’ value in the computed surface, this interpolates to produce the appropriate vectors at any ‘X’ value within the defined range of the surface.

Note that here the ‘Y’ matrix is transposed, since it was apparently created by meshgrid. It may be necessary to experiment by transposing the matrices depending on the particular surface created, and how they were defined (meshgrid or ndgrid, since their outputs are transposes of each other). My code here appears to work with the peaks function I chose to test it.

MATLAB: 2D contour plot with data in Matlab

Yoiur data are gridded. You only need to reshape your vectors to get the matrices necessary for any contour or 3D plots you want:

[D,S] = xlsread('Book1.xlsx');
[Ux,Ix] = unique(D(:,1));                               % Determine Frame Lengths
dIx = diff(Ix);                                         % Define Frame Length
Xr = reshape(D(:,1), dIx(1), []);                       % Create Matrix From Vector


Yr = reshape(D(:,2), dIx(1), []);                       % Create Matrix From Vector
Zr = reshape(D(:,3), dIx(1), []);                       % Create Matrix From Vector
figure
contourf(Xr,Yr,Zr)
xlabel('X')
ylabel('Y')

producing:

2D contour plot with data in Matlab - 2019 05 11.png

See the documentation on the contourf (link) function for details.

Experiment to get the result you want.

Best Answer

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MATLAB: How to get 2d line of surface plot section view

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