# Extract Gridded Data from Isosurface

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Paul Safier il 25 Mar 2021
Commentato: darova il 25 Mar 2021
I want to get the x, y and z data of a surface that I extract from a volume via isosurface. I am doing it in the following way, but I suspect that it's horribly inefficient (because I cannot believe there isn't a more straightforward way) and possibly inaccurate because of some of the results I have been getting. Can anyone suggest a simplier way?
I want the data at points given by (just an example):
[x,y] = meshgrid(linspace(0,10,30),linspace(0,10,30))
The data is available from this:
[faces,verts] = isosurface(Xa, Ya, Za, data, 0);
Then I am doing this to get the surface on the coordinates I want (x,y):
[X1,Y1,Z1] = xyz2grid(verts(:,1),verts(:,2),verts(:,3));
MySurface = interp2(X1,Y1,Z1,x,y);
NaNres = sum(isnan(MySurface(:)));
if NaNres > 0
MySurface = inpaint_nans(MySurface,3);
end
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darova il 25 Mar 2021
Everything looks ok. What is wrong?
Paul Safier il 25 Mar 2021
Modificato: Paul Safier il 25 Mar 2021
The results are the problem. It seems to work OK sometimes and awfully others. See example data and images of good surface (plotted by isosurface) and bad surface (plotted by surf after the interpolation). The raw data is attached that apply like this:
xx and yy are the results of meshgrid--they are where I want the z values.
[faces,verts] = isosurface(mesh_xs{:}, mesh_data, 0);
[X1,Y1,Z1] = xyz2grid(verts(:,2),verts(:,1),verts(:,3));
MySurface = interp2(X1,Y1,Z1,xx,yy);
NaNres = sum(isnan(MySurface(:)));
if NaNres > 0
MySurface=inpaint_nans(MySurface,3);
end
% Compare
figure; surf(xx,yy,MySurface)
figure; isosurface(mesh_xs{:}, mesh_data, 0);
Plotting with isosurface looks great (bottom figure). Plotting my interpolated result is bad (top figure).

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### Risposta accettata

darova il 25 Mar 2021
[faces,verts] = isosurface(mesh_xs{:}, mesh_data, 0);
zz = griddata(verts(:,2),verts(:,1),verts(:,3),xx,yy);
surf(xx,yy,zz)
Are you sure that the order xx and yy is correct?
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Paul Safier il 25 Mar 2021
That seems to work for the situation where the other method failed. Thanks for the suggestion!
darova il 25 Mar 2021
my plesure

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