How do I fit a surface to this data properly?

Question

Pablo Fernandez 2021-9-16

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链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1454104-how-do-i-fit-a-surface-to-this-data-properly

评论： Pablo Fernandez 2021-9-19

data.mat

Hi,

I have a set of datapoints (x,y,z) to which I want to fit a surface. I dont have a mathematical expression for the surface, so I tried to use the linear interpolation as in:

load ('data.mat')
PTSGRID = 256;
xs = min(x):(max(x)-min(x))/(PTSGRID-1):max(x);         
ys = min(y):(max(y)-min(y))/(PTSGRID-1):max(y); 
[xq, yq] = meshgrid(xs,ys); 
zq = griddata(x,y,z,xq,yq,'linear'); 
plot3(x,y,z,'mo')
hold on
mesh(xq,yq,zq);

However the fitted surface takes very strange values where there is no data defined, very different from what I would visually expect. Take a look for example at this figure, and the zone I circled:

How can I fit in a better way to avoid this behavior?

Thanks!

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darova 2021-9-17

Attach the data

Pablo Fernandez 2021-9-17

Attached to the original post!

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Answer 1

KSSV 2021-9-16

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1454104-how-do-i-fit-a-surface-to-this-data-properly#answer_788384

Read this: https://in.mathworks.com/help/curvefit/fit.html

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KSSV 2021-9-16

The same link has an example showing how to fit for a surface.

Pablo Fernandez 2021-9-16

Yes, I understand.

The specific point in my questions is how to get rid of the artifacts that appear when I try to interpolate the points in my dataset.

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Answer 2

darova 2021-9-19

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1454104-how-do-i-fit-a-surface-to-this-data-properly#answer_790564

data.mat

I don't have this problem

s = load('data.mat');

x = s.x;

y = s.y;

z = s.z;

xx = linspace(min(x),max(x),20);

yy = linspace(min(y),max(y),20);

[x1,y1] = meshgrid(xx,yy);

z1 = griddata(x,y,z,x1,y1);

Warning: Duplicate data points have been detected and removed - corresponding values have been averaged.

mesh(x1,y1,z1)

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Pablo Fernandez 2021-9-19

Hi, thanks for the answer.

You are not seing the effect in that plot because you are evaluating the interpolation in few points. The reason for the interpolation is to evaluate between the data lines. Try changing 20 for 256 in xx and yy definitions and you will notice the effect when plotting.

Regards

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