# How to draw a 3D surface with all the given discrete points？

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Danny le 4 Déc 2023
Commenté : Mathieu NOE le 4 Déc 2023
I am trying to draw data from several curves into a 3D surface. I have extracted the points in the curves as discrete data points and tried to draw a surface plot based on scatter data. The problem is that discrete points in each curve may have multiple Z-values at the same X-Y coordinate. Command 'griddata' and 'surf' have been used, but it gives warning of duplicate data points have been detected and averaged.
I have realized that the rule of 'griddata' is that only the unique Z-value can be used in the xy plane, otherwise the average will be used. The data is contained in the attachment, and the code and results are given below.
close all; clear all
scatter3(x,y,z)
% figure
[X,Y,Z]=griddata(x,y,z,linspace(min(x),max(x))',linspace(min(y),max(y)),'v4');
figure,surf(X,Y,Z);
figure,meshc(X,Y,Z)
How can I get a smooth surface with all the given data? Any comments will be much appreciated.
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### Réponse acceptée

Mathieu NOE le 4 Déc 2023
hello
of course I tried the standard solutions (surfir, griddata etc...) but as your shape is very specific , therefore also a specific code for you
try this
samples = numel(x);
[xu,ia,ic] = unique(x);
unique_curves = numel(ia);
N = samples/unique_curves; % this is length of one curve
% main loop
for k =1:N
ind = k:N:samples;
xx = x(ind);
yy = y(ind);
zz = z(ind);
% Interpolate the scattered data
xd(k,:) = linspace(min(xx),max(xx),100);
yd(k,:) = interp1(xx,yy,xd(k,:));
zd(k,:) = interp1(xx,zz,xd(k,:));
end
figure
subplot(1,2,1)
scatter3(x,y,z,8,'.k')
title('data points')
subplot(1,2,2)
h = surf(xd,yd,zd);
set(h,'edgecolor','none')
title('surface plot')
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Danny le 4 Déc 2023
Thank you! That's exactly what I wanted. You have solved my problem.
Best regards,
Danny
Mathieu NOE le 4 Déc 2023
my pleasure !

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### Plus de réponses (1)

Chunru le 4 Déc 2023
Modifié(e) : Chunru le 4 Déc 2023
whos
Name Size Bytes Class Attributes cmdout 1x33 66 char x 2870x1 22960 double y 2870x1 22960 double z 2870x1 22960 double
figure
T = delaunay(x, y);
Warning: Duplicate data points have been detected and removed.
Some point indices will not be referenced by the triangulation.
% Seems that there are duplicate point for x, y (in addition to z?)
trisurf(T, x, y, z, "EdgeColor","none", "FaceColor","interp");
xlabel("x"); ylabel("y")
view(80, 30)
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Danny le 4 Déc 2023
Thanks Chunru.
Perhaps I should explain my question further. Actually, these discrete data come from 5 curves, and I want to draw a surface that contains these curves. In other words, I want to restore these data completely on a surface. Commands "trisurf" or "surf" do give the rough shape of the surface, but the key is how to preserve these duplicate values.

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