Get regular grid and points of a given stl file

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Diego Hens
Diego Hens 2020 年 8 月 14 日
コメント済み: Diego Hens 2020 年 8 月 21 日
Hello,
I have have a stl file, which has many points (ca. ten thousand) but they are not uniformly distributed. As you know, a stl object has Faces, Vertices and Normals. The Vertices are the points (they can be repeated a few times, depending on how many triangles you can form with them).
I would like to create points in between the vertices (I don't care if I lose these initial points) so that they are evenly distributed. Imagine I project the object (just the points) in a 2D plane. I would like the points to be regularly distributed (like a grid but without the lines).
  4 件のコメント
KSSV
KSSV 2020 年 8 月 17 日
Any pictorial example?
Diego Hens
Diego Hens 2020 年 8 月 17 日
sorry, I answered on the wrong spot. Can you take a look on my other comment?

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採用された回答

Bruno Luong
Bruno Luong 2020 年 8 月 18 日
編集済み: Bruno Luong 2020 年 8 月 21 日
I load the stl, cleanup the vertices, compute the face normal then I extract the top cap and interpolate on grid.
% Read mesh and compute normal vector
TR = stlread('Zahn_15_Bibliotheksmodell.stl'); % contains "Mesh" structure
[X,~,J] = unique(TR.Points,'rows');
F = J(TR.ConnectivityList).';
X = X.';
XF = reshape(X(:,F),3,3,[]);
N = cross(XF(:,2,:)-XF(:,1,:),XF(:,3,:)-XF(:,2,:),1);
% Extract the points on the top cap
Fup = F(:,N(3,:)>0);
Fup = sort(Fup,1);
n = max(Fup(:));
A = accumarray([Fup([1 2],:), Fup([1 3],:), Fup([2 3],:)]', 1, [n,n], [], 0, true);
G = graph(A+A');
bins = G.conncomp;
n = accumarray(bins(:),1);
[~,icap] = max(n);
icap = find(bins==icap);
Xcap = X(:,icap);
x = Xcap(1,:);
y = Xcap(2,:);
z = Xcap(3,:);
% Interpolation on grid
xmin = min(x); xmax = max(x);
ymin = min(y); ymax = max(y);
nx = 513; ny = 513; % define resolution of grids
xi = linspace(xmin,xmax,nx);
yi = linspace(ymin,ymax,ny);
[XI,YI] = meshgrid(xi,yi);
I = scatteredInterpolant(x(:),y(:),z(:),'linear','none');
ZI = I(XI,YI);
% Plot the result
figure(1);
ax=subplot(1,2,1);
imagesc(ax,xi,yi,ZI);
set(ax,'Ydir','normal','clim',[28 31])
colormap(ax,gray);
axis(ax,'equal');
axis(ax,'tight');
ax=subplot(1,2,2);
surf(ax,xi,yi,ZI,'linestyle','none');
There are some artefact, and did not try to see why, but it gives you an idea.
  4 件のコメント
Bruno Luong
Bruno Luong 2020 年 8 月 20 日
I edit with code to create mesh F and X and N manually
Diego Hens
Diego Hens 2020 年 8 月 21 日
I'm a bit slow, but I think I've got it now (not really the code, but the problem in itself). Your answer was actually what I looked for (the part where you extract the points on the top cap I did not understand, but I could use the rest still). I think I can go on from here.
I have accepted it as an answer for this reason.
I will try to find out why there is noise and if I can avoid it. If not, I will look for other methods.
Thank you again, Bruno :D

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その他の回答 (1 件)

Diego Hens
Diego Hens 2020 年 8 月 17 日
Ok, here's what I got.
Imagine the triangle on the left side was my object. It has values in X, Y and Z. I want to project the object into the XY plane (as in the right) and represent the Z value with a grayscale value. If I project the object I get the drawing ob the right. As I have only three vertices, I will only get three points with a grayscale value. That means (especially if the object is bigger) that I will have many holes, where no value Z is given, as there is no point.
I would like to be able to interpolate these values in between, so that I have no (or very little) holes.
Is the problem understandable now?
Thanks for the help :D
  7 件のコメント
Diego Hens
Diego Hens 2020 年 8 月 18 日
I think that's exactly what I want. This is what I get:
F = scatteredInterpolant with properties:
Points: [25634×2 double]
Values: [25634×1 double]
Method: 'linear'
ExtrapolationMethod: 'linear'
How can I plot this now?
Bruno Luong
Bruno Luong 2020 年 8 月 18 日
The difficult part is you need to filter the points and keep only the point on the cap of the tooth. Because - as I said - your data is not of the form z=f(x,y) and there are multiple z for the same (x,y) (close to the boundary if one looks from the above). This will polute the interpolation.

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