Find Z-value corresponding to X and Y points based on interpolated data

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Lai Ping on 6 Jan 2023
Answered: Karim on 6 Jan 2023
I would like to perform 2D interpolation for scatter data that is supported by Matlab Coder package.
I have a set of data, with x,y and z cordinates, in the following format.
X Y Z
1 2 10
2 2 8
2 4 9
3 2 9
3 4 10
3 6 9
So at Z(1,2) = 10, Z(2,2) = 8 and so on.
I wish to find the value of Z(1,3), Z(3,1) for example and eventually output the code to C/C++ using Matlab Coder package.
I tried using griddata and scatterInterpolant which is what I wish to achieve, however, it is not supported by Coder package. So I tried to work with interp2 or gridedInterpolant, however I am not sure how to convert my sample data to full grided form.
Is there any way to convert the above data to be used ny interp2 or gridedInterpolant?
Or is there other function that I can use and I wasn't aware of that?
Appreciate for any help! Thanks!
VBBV on 6 Jan 2023
Lai Ping on 6 Jan 2023
I tried and I get error, sample points must be unique.
Here is my code, I am not sure where I did made mistake. Does it matter if I have duplicated value in x vector and y vector?
x=[1,2,2,3,3,3];
y=[2,2,4,2,4,6];
z=[10,8,9,9,10,9
10,8,9,9,10,9
10,8,9,9,10,9
10,8,9,9,10,9
10,8,9,9,10,9
10,8,9,9,10,9];
xCor=0:3;
yCor=0:3;
[xx,yy] = meshgrid(x,y);
zz = interp2(xx,yy,z, xCor, yCor)

Karim on 6 Jan 2023
Note that you have very little points. Hence one possibility is to perform linear interpolation, below you can see one method on how to do this.
% original data by OP
x = [1 2 2 3 3 3]';
y = [2 2 4 2 4 6]';
z = [10 8 9 9 10 9]';
% plot the points in 3D space
figure
scatter3(x,y,z,'r','filled')
grid on; view([-70 30]);
title('Original points')
% set up the grid for the interpolation
x_fine = linspace(min(x),max(x),20);
y_fine = linspace(min(y),max(y),20);
[Xq,Yq] = meshgrid(x_fine,y_fine);
% create a linear fitting trough the points
sfun = fit([x, y],z,'linearinterp');
Zq = feval(sfun,Xq,Yq);
% plot the results
figure
surf(Xq,Yq,Zq)
grid on; view([-70 30])
title('Surface through interpolated points')
figure
scatter3(Xq,Yq,Zq,'g','filled')
grid on; view([-70 30])
title('Interpolated points')

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