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# How do I plot 3d graph ?

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Urvashi Agrawal on 24 May 2021
Commented: Star Strider on 25 May 2021
So I have this 26x4 matrix and I need to plot a 3d matrix for the first 3 coloumns. The following is my code :
impval = xlsread('Values_sweep.xlsx');
vol_data = impval(1:end,1); %data.VolumeSystem
density_data = impval(1:end,2); %data.PowerDensity
power_data = impval(1:end,3);%data.Power
distance_data = impval(1:end,4);%data.distance
x = vol_data;
y = power_data;
z = density_data;
[X,Y] = meshgrid(x,y);
How do I then plot in 3d. I want to plot for the vol_data, density_data and power_data but I'm getting error 'Z must be a matrix , not a scalar or vector'
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### Answers (3)

VBBV on 24 May 2021
%if true
Z = repmat(z,1,length(X))
surf(X,Y,Z)
Z is your density data
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Urvashi Agrawal on 25 May 2021
This is what I'm obatining after playing around with the code.
Quite close to the graph I want but I was looking more like the following , if possible

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Jonas on 24 May 2021
what about plot3(x,y,z) without the meshgrid?
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Urvashi Agrawal on 24 May 2021
I tried it , but I'm more interested in having a proper surface /mesh grid plot .

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Star Strider on 24 May 2021
Interpolate!
N = 50;
xv = linspace(min(x), max(x), N);
yv = linspace(min(y),m max(y), N);
[Xm,Ym] = ndgrid(xv, yv);
Zm = griddata(x, y, z, Xm, Ym);
figure
surfc(Xm, Ym, Zm)
grid on
See the griddata documentation for details.
This is prototype code. Note than ‘N’ can be any value that works, and does not have to be the same for both ‘xv’ and ‘yv’.
.
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Star Strider on 25 May 2021
The data are the data.
Note — The x-axis is the scale of the y-axis and z-axis. If you want to plot it as a (relatively narrow) surface that may be more representative, use:
axis('equal')
after the surf call.
If you plot it with plot3 or scatter3, the plot should look similar to what you got with my code. Another option is stem3 if you want to see precisely where on the (x,y) plane the points originated.
.

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