Find holes and gaps in .stl files

Hi,

I need to find gaps and holes in a stl file. I don´t know if there´s a function developed that can help me. I started to work with MATLAB recently and i´m finding some dificulties. I found 2 ways of doing this, each triangle should have 3 adjacent triangles or each edge must have 2 triangles in common. Hope someone could give a hand. Thank´s.

Eduardo G.

[agdfg sdgfdg]

Hello,iam a very beginner of MATLAB.I import the STL file in ASCII format and try to run the code of Sven,but it is generating errors.Can you please elaborate the steps please.

[Walter Roberson]

Please be more specific about the errors you are observing.

[agdfg sdgfdg]

[unqEdges, ~, edgeNos] = unique(edges,'rows'); | Error: Expression or statement is incorrect--possibly unbalanced (, {, or [. this the error i observed.

And i request you to suggest some other algorithms or codes for STL File Correction.

Answer 1

[Sven]

Hi Eduardo,

Firstly you need to read the .stl file in as faces and vertices. I'll presume you've already got that done (as Anton points out, stlread is available here http://www.mathworks.com/matlabcentral/fileexchange/22409-stl-file-reader).

Next, as you wrote: each edge must have 2 triangles in common... I think this is a good start. Here's some code that will make a test faces/vertices mesh, then determine such a thing:

% MAKE a face/vertices structure
tmpvol = zeros(20,20,20);       % Empty voxel volume
tmpvol(8:12,8:12,5:15) = 1;     % Turn some voxels on
fv = isosurface(tmpvol, 0.99);

% REMOVE a face 
fv.faces(30,:) = []; % Remove a face!

% TEST for gaps or holes
edges = sort(cat(1, fv.faces(:,1:2), fv.faces(:,2:3), fv.faces(:,[3 1])),2);
[unqEdges, ~, edgeNos] = unique(edges,'rows');
if size(edges,1) == size(unqEdges,1)*2
    % Every edge is used twice... consistent with a closed manifold mesh
    disp('No problem!')
else
    badEdgesMask = hist(edgeNos, 1:max(edgeNos))~=2;
    badEdgeNos = edgeNos(badEdgesMask);
    badNodeNos = edges(badEdgeNos,:);
    badFaceNos = find(sum(ismember(fv.faces, badNodeNos),2)>=2);
end

Does this answer the question for you?

[Eduardo]

Thanks. This is exactly what i was looking for. Now i have to fill in the hole if one or more were found... Do you have any idea how to do it?

[mahmoud elmesery]

Hello, How to substract two stl files in matlab

Answer 2

[Eduardo]

Hi,

First of all thanks. I´m using this 'stlread':

http://www.mathworks.com/matlabcentral/fileexchange/29906-binary-stl-file-reader/content/stlread.m

and then i´m using 'patchslim'. Now i´ll try your code and i´ll give you feedback.

Answer 3

[Eduardo]

Hi. I´ve made some tests and discovered that when a hole is found this code is not working correctly. When we axecute "badEdgeNos = edgeNos(badEdgesMask);" this should compare badEdgesMask with the number 1 and not with the first element of edgeNos. Can you understand what i´m trying to explain?

[Sven]

If you mean that the variable badEdgesMask only contains ones and zeros, then you need to realise that it's using logical indexing... if you're sure there's a problem, make a small example (such as the one I made) and show how it's not working.

[Eduardo]

I´ve made a test with a simple cube. I removed 1 face and badEdgesMask is correct. The problem is in "badEdgeNos = edgeNos(badEdgesMask);" because badEdgesMask has 18 elements and edgeNos has 33. The comparison is made 1 by 1 element, so it compares the first logical value with the first element of edgeNos, i think it should be the first logical value with the element 1 of edgeNos (corresponding edge "1 2").

Answer 4

[Eduardo]

I made it like this to solve the problem i´ve told you:

edges = sort(cat(1, fv.faces(:,1:2), fv.faces(:,2:3), fv.faces(:,[3 1])),2);
[unqEdges, ~, edgeNos] = unique(edges,'rows');
if size(edges,1) == size(unqEdges,1)*2
    % Every edge is used twice... consistent with a closed manifold mesh
    disp('No problem!')
else

      badEdgesMask = hist(edgeNos, 1:max(edgeNos))~=2;  
      [~, ~, edgeNos1] = unique(unqEdges,'rows');
       badEdgeNos = edgeNos1(badEdgesMask);  
      badNodeNos = unqEdges(badEdgesMask,:);
      badFaceNos = find(sum(ismember(fv.faces, badNodeNos),2)>=2);
  end

I don´t know if this the best way to do it, but it works...

[Muhammed Talu]

How can I get deleted faces back?