How to remove outliers in a 3D surface
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I have a 3D surface (see below) construced using surf command based on excel data:
T = readtable('https://in.mathworks.com/matlabcentral/answers/uploaded_files/791474/excel-surface.xlsx')
x = T.(1) ;
y = T.(2) ;
z = T.(3) ;
xi = linspace(min(x),max(x));
yi = linspace(min(y),max(y)) ;
[X,Y] = meshgrid(xi,yi) ;
Z = griddata(x,y,z,X,Y) ;
surf(X,Y,Z)
shading interp
colorbar
The resulting surface is as follows:
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/792089/image.png)
However, I know that the surface should be smooth without these "peaks" that appear randomly from above or below.
Is there a way to remove these outliers and interpolate to construct a smooth surface? (NOTE, I AM NEW TO MATLAB).
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Antworten (2)
Chris
am 6 Nov. 2021
Bearbeitet: Chris
am 6 Nov. 2021
I would recommend trying the "clean outlier data" task in the live editor, after sorting the data:
T = sortrows(T,1); % Sort by the first column ('x')
Open a New Live Script, and select the task.
Select the table and input variable z.
I can get decent results with spline interpolation, a centered moving median, and a low threshold. But I'm not sure how, computationally, you would create a perfectly smooth surface that retains the contours you would want to see, as there are quite a few clumped outliers.
Perhaps repeated sorting by x and y, with outlier cleaning in between, could work.
2 Kommentare
Chris
am 7 Nov. 2021
clear; clc;
% Read table:
T = readtable('https://in.mathworks.com/matlabcentral/answers/uploaded_files/791474/excel-surface.xlsx');
% Fill outliers:
for idx = 1:2
for jdx = 8:-2:2
T = sortrows(T,1);
T.Z = filloutliers(T.Z, "spline", "movmedian", jdx);
T = sortrows(T,2);
T.Z = filloutliers(T.Z, "spline", "movmedian", jdx);
end
end
% Plot surface:
x = T.(1) ;
y = T.(2) ;
z = T.(3) ;
xi = linspace(min(x),max(x));
yi = linspace(min(y),max(y)) ;
[X,Y] = meshgrid(xi,yi) ;
Z = griddata(x,y,z,X,Y) ;
surf(X,Y,Z)
% shading interp
colorbar
Getting pretty close.
With default shading, you'll see there are still a few bumps. But you can also see interesting features. Repeating the process, and changing the window size, continues to smooth the surface.
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