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How could I separate the geometry data from single stl file contains multiple objects by stlread?

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Daniel Chou
Daniel Chou on 4 Feb 2021
Edited: Daniel Chou on 4 Feb 2021
Dear all, I have a question about stlread!
The scenario is that I have a stl file with two non-overlap ellipses in it as attached.
But when I using stlread function in Matlab.
I obtain the points coordinates and connectivity list of faces of both ellipses TOGETHER.
I wondering is there any method to separate the information of two ellipses?
For regular shapes this might not be a big problem, however, If I have 100 irregular objects with eac of them has different number of faces and vertices, it will be difficult to use since it's very hard to specify the information of each object.
I just try to start to separate them, but then I have no further idea.
Attached are my codes, with stl file in zip format.
F=stlread('research_stl_read.stl')
con_list=F.ConnectivityList
face_num=length(con_list(:,1))
Could anyone give me a hand?
I appreciate for your patience
Sincerely yours~!
Daniel
  1 Comment
KSSV
KSSV on 4 Feb 2021
It can be seperated.....you need to have a look on the data to do this. Attach your stl file. And the lines of code which you tried to plot the attached.

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Accepted Answer

Bruno Luong
Bruno Luong on 4 Feb 2021
Edited: Bruno Luong on 4 Feb 2021
You can use conncomp of the triangulation graph
data=stlread('research_stl_read.stl');
s=data.ConnectivityList(:,[1 2]);
t=data.ConnectivityList(:,[2 3]);
G=graph(s(:),t(:));
I=G.conncomp;
u=unique(I);
P = data.Points;
T = data.ConnectivityList;
clear Obj
for i=1:length(u)
j = find(I==i);
Pi = P(j,:);
[b,Ti] = ismember(T,j);
Ti = Ti(all(b,2),:);
Obj{i} = triangulation(Ti,Pi);
end
figure();
subplot(2,2,[1 2]);
trimesh(data);
for i=1:length(Obj)
subplot(2,2,i+2);
trimesh(Obj{i} );
end
  2 Comments
Daniel Chou
Daniel Chou on 4 Feb 2021
Dear Bruno Luong,
May I ask for a question?
Your codes are amazing, It complete the works of the complex geometry in only 5 secs (as attached).
But I wish I could know more about the mechanism of it.
I don't quite understand that why you design these three lines:
s=data.ConnectivityList(:,[1 2]);
t=data.ConnectivityList(:,[2 3]);
G=graph(s(:),t(:));
I checked the illustration of graph object and conncomp.
But I couldn't understand yet.
You could answer this only if oyu have time.
Thank you very much again!
Sincerely
Daniel

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