清空筛选条件
清空筛选条件

Find a plane that is tangent to a part of the 3D model

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Tingting
Tingting 2021-11-16
编辑： Matt J 2021-11-23
Hello!
I have got a 3D model and I want to find a 2D plane that is tangent to the bottom of my 3D model. The bottom is made up of three sphere-like structures spliced together. I want to know how to find such a plane to make it tangent to the bottom? There should be three tangent points.
The following figure attaches my 3D model and schematic diagram
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Tingting
Tingting 2021-11-16
编辑：Tingting 2021-11-16
I had stl format. Here is my model, thank you very much!
Tingting
Tingting 2021-11-16
Let me explain in detail. In my previous work, I have obtained the 3D model of the aortic root of the human body through automatic segmentation of the neural network. This plane is called the aortic annulus plane. My task is to search for this plane to obtain the aortic annulus (the circle obtained by three tangent points) diameter. Thank you for your attention!

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Matt J
Matt J 2021-11-16
编辑：Matt J 2021-11-18
Obtain all the mesh vertices from your stl file in V. Then, compute the facet areas and normals of the convex hull with,
k=convhull(V);
dVa=V(k(:,2),:)-V(k(:,1),:);
dVb=V(k(:,3),:)-V(k(:,1),:);
C=cross(dVa,dVb);
Areas=vecnorm(C,2,2); %facet areas
Normals=normalize(C,2,'norm'); %facet normals
From your diagram, your three spheres look to be within about 10 degrees of the direction vector d=[2 0 1]/sqrt(3), so,
d=[2 0 1]'/sqrt(3);
subset=find(acosd(abs(Normals*d))<30);
[~,i]=max(Areas(subset));
kp=k(subset(i),:);
Vp=V(kp,:); %The 3 annulus vertices
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Tingting
Tingting 2021-11-23
Excuse me, could you please share your code here, I don't know how to show mesh vertices .
Matt J
Matt J 2021-11-23
编辑：Matt J 2021-11-23
Ran in:
I just used scatter3. You could have used tetramesh() or plot3() or anything you like.
load meshvertices
XYZ=num2cell(V,1)';
scatter3(XYZ{:},'filled','MarkerEdgeColor','none','MarkerFaceAlpha',0.1)

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