Deformed surf using griddata ?
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Faez Alkadi on 24 Aug 2017
Commented: Faez Alkadi on 25 Aug 2017
I have a set of data as attached. but when I surf them after using griddata. the result is deformed surf AS SHOWN IN THE PICTURE with red squares. Z values on the surf were supposed to follow the edges of the shape. I think its because there is something wrong with (z_surf) matrix in my code. But I don't know how to solve it.
Hope you can help me to solve this problem.
John D'Errico on 24 Aug 2017
Edited: John D'Errico on 24 Aug 2017
Griddata will fail here. In fact, my own gridfit will produce some artifacts.
But essentially, you have a simple ribbon of the form z(y), which seems to be independent of x.
x = xyzSTL_board_ordered_dvd(:,1);
y = xyzSTL_board_ordered_dvd(:,2);
z = xyzSTL_board_ordered_dvd(:,3);
There is NO x in that relationship. So all you need to do is fit the curve z(y). Use a spline. Start out by removing any replicates. Using my consolidator tool, as found on the file exchange :
[yhat,zhat] = consolidator(y,z,@mean);
spl = pchip(yhat,zhat);
Use pchip here. This is fairly important.
[xgrid,ygrid] = ndgrid(linspace(min(x),max(x),10),linspace(min(y),max(y),100));
zgrid = repmat(ppval(spl,linspace(min(y),max(y),100)),10,1);
More Answers (1)
You can get closer to what you want if you add the 'nearest' option to the griddata() call.
You will get an odd artifact, which I figure is due to peculiarities about which is the "closest" point in 3-space.
There is no reason for the surface to follow the edge using griddata(). Gridding takes place in 3-space, so when you get sufficiently far from the edges, the closest points might be from a different z than you were picturing.
If you have a surface that you know should be a ribbon, then there are ways to decompose that.
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