Interpolate pairs of values from matrix

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Chris Pruefert
Chris Pruefert 2024-10-3
评论： Mathieu NOE 2024-10-11
I have a coarse 2D-matrix with [X,Y,Z]-values.
I want to input a Z-value and would like to interpolate possible values for the [X,Y]-pairs. These [X,Y]-pairs are then used for a fit. This means that for a given value of Z, if I choose any X value, Y can be calcualted and the other way arround.
I have tried the interp2 already, but it seems that I can only input X and Y values to get the interpolated Z value and not the other way around, where I input a Z-value and get a list of [X,Y]-pairs for that.
All the best
Chris
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Chris Pruefert
Chris Pruefert 2024-10-11
Esaclty, the value for Z most likely is not listed in the original coarse matrix. This means, that the corresponding X and Y value most likely will have to be interpolated from the coarse grid of Z. Would that be possible?
Chris Pruefert
Chris Pruefert 2024-10-11
To grab this example matrix, in the first colum if X=125, 0.3 is inbetween Z = 0.247 and 0.389, with Y = 4.459 4.526 respectively. Eliminating the NaN, interp1(Z(:,1),Y,0.3) would then give 4.4838. Is that the way to do it?

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Mathieu NOE
Mathieu NOE 2024-10-3
Ran in:
hello
you can surely get the required x , y data for a given z value ; use contour for that purpose as shown in code example below :
Z = peaks(50)/10;
level = 0.3;
surf(Z)
hold on
% extract all isoclines for a given level
[C,h] = contour(Z,level*[1 1]);
[m,n] = size(C);
ind = find(C(1,:)==level); % index of beginning of each isocline data in C
ind = [ind n+1]; % add end (+1)
for k = 1:numel(ind)-1
xc = C(1,ind(k)+1:ind(k+1)-1);
yc = C(2,ind(k)+1:ind(k+1)-1);
zc = level*ones(size(xc));
plot3(xc,yc,zc,'linewidth',5);
end
hold off
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Chris Pruefert
Chris Pruefert 2024-10-11
Yes, that is exactly what I tried to achieve. Thanks

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