how to tell apart faces of a 3d geometry for pde model?

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yonatan s 2017-5-22

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https://ww2.mathworks.cn/matlabcentral/answers/341295-how-to-tell-apart-faces-of-a-3d-geometry-for-pde-model

评论： yonatan s 2017-5-24

hello, i created a 3d geometry for my pde model, but it is not so clear what are the faces refering to. is there any way to clearly distinguish them?

thanks

a=25/6; %semi major axis
%generate alphashape
[az,el,r] = meshgrid(linspace(0,2*pi-0.01,60),linspace(-pi,0,60),[0.99,1]);
[x,y,z] = sph2cart(az,el,r);
x=x*a;
y=y*a;
z=z+1;
shp = alphaShape(x(:),y(:),z(:),0.25);
% plot(shp);
%applying the geometry to the model
[elements,nodes] = boundaryFacets(shp);
nodes = nodes';
elements = elements';
model = createpde();
geometryFromMesh(model,nodes,elements);
pdegplot(model,'FaceLabels','on','FaceAlpha',0.5);

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Alan Weiss 2017-5-22

在 MATLAB Online 中打开

When I tried to create the geometry in MATLAB R2017a using your script, I got the following error:

Failed to create geometry. The stl file is invalid, more than two facets share an edge.

Alan Weiss

MATLAB mathematical toolbox documentation

yonatan s 2017-5-22

编辑：yonatan s 2017-5-22

sorry, variable a suppose to be equal to 25/6.

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Answer 1

Alan Weiss 2017-5-23

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https://ww2.mathworks.cn/matlabcentral/answers/341295-how-to-tell-apart-faces-of-a-3d-geometry-for-pde-model#answer_268127

Thanks for correcting the description. If you zoom in to an edge near the F3 label, you can see that F3 is the ring that bounds the two spheroidal faces, meaning it is the ring whose width is the thickness of this solid body. F2 represents the upper face (higher Z-coordinate). And F1 is the lower face (lower z-coordinate).

Alan Weiss

MATLAB mathematical toolbox documentation