How to fix the incorrect shape of a mesh

Question

Mohammad Abu Haifa 2022-9-1

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https://ww2.mathworks.cn/matlabcentral/answers/1792060-how-to-fix-the-incorrect-shape-of-a-mesh

回答： Mohammad Abu Haifa 2022-9-1

I have 3D points that represent a cuboid saved in F which I extracted from an image. F is 8x3 double array. When I converted the data to a triangulated mesh and plotted it, I got this incorrect shape, see the image below. It should produce a cuboid with 6 faces, but the resulted one has 8 faces. Anyone can help me how to fix the problem to plot the correct shape? However, when I write the values of x,y, and z manually (see the code below the image), the code plots the shape correctly.

The code is:

x = F(:,1);
y = F(:,2);
z = F(:,3);
shp = alphaShape(x,y,z);
[elements,nodes] = boundaryFacets(shp);
model = createpde();    % requires Partial Differential Equation Toolbox 
geometryFromMesh(model,nodes',elements');
pdegplot(model,'FaceLabels','on','FaceAlpha',0.5)
generateMesh(model);

% This section is the manual values of x, y, and z. Here the plot is correct. But if I use the existed one, the plot is not correct
F = [0.014	-0.4472	0
4055	-0.4472	0
409	-0.6478	0
014	-0.6478	0
014	-0.4472	-0.18
4055	-0.4472	-0.18
409	-0.6478	-0.18
014	-0.6478	-0.18];

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Answer 1

Mohammad Abu Haifa 2022-9-1

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https://ww2.mathworks.cn/matlabcentral/answers/1792060-how-to-fix-the-incorrect-shape-of-a-mesh#answer_1039180

I found the answer. To fix this problem we need to arrange the vertices order. So, you can do the following:

K = convhull(x,y,z);

nodes = [x';y';z'];

elements = K';

model = createpde();

geometryFromMesh(model,nodes,elements);

pdegplot(model,'FaceLabels','on','FaceAlpha',0.5)

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Answer 2

KSSV 2022-9-1

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1792060-how-to-fix-the-incorrect-shape-of-a-mesh#answer_1039165

Refer this: https://in.mathworks.com/matlabcentral/fileexchange/15161-plotcube

You need to arrange the vertices in an order...get the order from the above file exchange..

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Mohammad Abu Haifa 2022-9-1

This is a different story. I want to keep it as a mesh (not only a plot) because I want to export the mesh to nother software. The problem is the number of faces of the mesh is correct when I enter the values manually, but when I use the 3D data extracted from an image, the mesh has two more faces.