AlphaShape: incorrect geometry
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Irene Yang
le 12 Mar 2019
Commenté : Steven Lord
le 12 Mar 2019
Hi,
I have a 3D CAD file which I am importing into Matlab via stlread.
I then use alphaShape using the points generated from stlread of the geometry. However, the alphaShape is not accurate to my geometry and adds a whole bunch of triangles that do not match my geometry.
This is what it is supposed to be:
However, this is what I get instead:
How can I fix this? Does anyone have an idea on how I could possibly go in and edit the triangulation (is this even feasible?)? Or alternatively, another function in matlab that can allow me the same thing as alphaShape? Should I edit the mesh further? I have tried everything that I can think of!
Thanks.
4 commentaires
Jan
le 12 Mar 2019
Modifié(e) : Jan
le 12 Mar 2019
alphaShape is used to define a surface based on a point cloud. As Sean has written already, you do have a surface already, so there is no need for alphaShape.
But your problem seems to be, that you used inapropriate values for 'RegionThreshold' or 'HoleThreshold' or 'Alpha' radius. Which values did you use? Please post your code.
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Sean de Wolski
le 12 Mar 2019
2 commentaires
Steven Lord
le 12 Mar 2019
See the "Enclosing Tetrahedra" example.
x = gallery('uniformdata',[20 1],0);
y = gallery('uniformdata',[20 1],1);
z = gallery('uniformdata',[20 1],2);
TR = delaunayTriangulation(x,y,z);
P = [0.7 0.6 0.3; 0.5 0.5 0.5];
[ID,B] = pointLocation(TR,P)
I'll plot the delaunayTriangulation using tetramesh and turn off the face colors.
h = tetramesh(TR, 'FaceColor', 'none');
Now I'll add the two points inside.
hold on;
plot3(P(:, 1), P(:, 2), P(:, 3), 'ro', 'MarkerFaceColor', 'r')
Finally I'll color the tetrahedron containing the first point in blue and make it somewhat transparent.
set(h(ID(1)), 'FaceColor', 'b', 'FaceAlpha', 0.25)
If you rotate the axes around you should be able to convince yourself that one of the red dots is inside the blue shape. It looks like it's very close to the surface of the shape but inside.
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