Unable to plot 3D graph
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I am trying to plot velocity data contained within a 2D plane (x-y). I would like to plot a 3D graph to present this. However, when trying to plot, I get an error stating
'Error using surf
Z must be a matrix, not a scalar or vector.'
The data is imported from an excel file and the appropriate columns are turned into arrays of x, y and U as shown below:
tbl = readtable('2D1mat.xlsx');
x=tbl.Var1;
y=tbl.Var2;
U=tbl.Var3;
surf(x,y,U)
I have also ensured that the input arguments for surf are all matrices with the help of ismatrix.
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Torsten
le 7 Nov 2022
Doesn't look very impressive, does it ?
A = readmatrix("https://de.mathworks.com/matlabcentral/answers/uploaded_files/1184273/2D1mat.xlsx");
x = A(:,1);
y = A(:,2);
u = A(:,3);
F = scatteredInterpolant(x,y,u);
xq = 33.5:1:53.5;
yq = 45:0.25:48.25;
[XQ,YQ] = meshgrid(xq,yq);
UQ = F(XQ,YQ);
surf(XQ,YQ,UQ)
2 commentaires
Torsten
le 7 Nov 2022
Modifié(e) : Torsten
le 7 Nov 2022
Or the adapted solution from Star Strider:
A = readmatrix("https://de.mathworks.com/matlabcentral/answers/uploaded_files/1184273/2D1mat.xlsx");
x = A(:,1);
y = A(:,2);
z = A(:,3);
N = 100;
xv = linspace(min(x), max(x), N);
yv = linspace(min(y), max(y), N);
[X,Y] = ndgrid(xv, yv);
Z = griddata(x, y, z, X, Y, 'linear');
figure
surfc(X, Y, Z)
grid on
colormap(turbo)
colorbar
xlabel('X')
ylabel('Y')
zlabel('Z')
Plus de réponses (1)
Star Strider
le 7 Nov 2022
The ismatrix function wil return true for a vector and for a 2D matrix. It returns false for arrays with more than 2 dimensions.
The vectors may actually represent gridded data and so would form matrices when the vectors are appropriately reshaped.
An approach that may work (since we do not have the vectors to work with) —
x = rand(1,10);
y = rand(1,10);
z = rand(1,10);
N = 25;
xv = linspace(min(x), max(x), N);
yv = linspace(min(y), max(y), N);
[X,Y] = ndgrid(xv, yv);
Z = griddata(x, y, z, X, Y, 'linear');
figure
surfc(X, Y, Z)
grid on
colormap(turbo)
colorbar
xlabel('X')
ylabel('Y')
zlabel('Z')
.
2 commentaires
Star Strider
le 7 Nov 2022
There is actually no need to interpolate this, since the data are gridded, as the stem3 plot demonstrates.
For some reason, ‘Var2’ does not work with reshape as it should, despite a fair amount of effort to get it to. I finally gave up on that and went with repmat. Anyway, if all goes well, all the matrices are (14x21) and the surface plots correctly.
I checkked the surf plot against the stem3 plot, and they essentially agree. (The log transformation is necessary to get the stem3 plot to show any variation in Z, since the magnitudes of the third column don’t vary much. Without it, the stem3 plot hides what little variation there is.)
T1 = readtable('https://www.mathworks.com/matlabcentral/answers/uploaded_files/1184273/2D1mat.xlsx')
figure
stem3(T1{:,1}, T1{:,2}, T1{:,3}, '.')
hold on
scatter3(T1{:,1}, T1{:,2}, T1{:,3}, 25, T1{:,3}, 'filled')
hold off
grid on
colormap(turbo)
xlabel('X')
ylabel('Y')
zlabel('Z')
set(gca, 'ZScale','log')
% view(0,90)
[U1,ix1] = unique(T1{:,1});
U1
rowlen = numel(U1)
[U2,ix2] = unique(T1{:,2});
U2
collen = numel(U2)
% X = reshape(T1{:,1}, rowlen, collen)
% Y = reshape(T1{:,2}, rowlen, collen)
X = repmat(U1,1,collen).';
Y = repmat(U2,1,rowlen);
Z = reshape(T1{:,3}, collen, rowlen);
figure
surfc(X, Y, Z)
grid on
colormap(turbo)
xlabel('X')
ylabel('Y')
zlabel('Z')
set(gca, 'ZScale','log')
% shading('interp')
.
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