Create STL from patch object or simlar

Question

Holden Tranquillo 2022-3-3

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1662345-create-stl-from-patch-object-or-simlar

评论： Holden Tranquillo 2022-4-7

Hello,

Currently, I have several matrices that represent the (x,y) coordinates for contours. In the image shown, I am just plotting those contours using the 'patch' command. What I need to do, however, is export these contours (either individually, or all at once) as an STL file to be opened in a CAD software.

Matlab's 'stlwrite' command only accepts a triangulation object as an argument. However, currently, when I try to create a triangulation of one of the contours (in the image shown it is of the outermost contour), I get a distorted and incorrect representation.

It seems like this should be a simple task to do, so any help would be greatly appreciated.

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Holden Tranquillo 2022-3-3

Contours.mat

Here are the contours. Thanks for taking a look

Holden Tranquillo 2022-3-5

So it looks like you do the delaunayTriangulation w/ constraints is so that the the edges are known to Matlab for when you do 'isInterior'?

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Answer 1

KSSV 2022-3-3

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https://ww2.mathworks.cn/matlabcentral/answers/1662345-create-stl-from-patch-object-or-simlar#answer_908445

在 MATLAB Online 中打开

load('Contours.mat') ;
p = [perimeter1 ; perimeter2 ; perimeter3 ; perimeter4 ; perimeter5 ; perimeter6 ; perimeter7 ; perimeter8 ;
     perimeter9] ;
 
id = knnsearch(p,perimeter1) ; 
C = [id(1:end-1) id(2:end)]; 
% Make delaunay triangulation with constriants 
dt = delaunayTriangulation(perimeter1,C) ;
% Get the interior triangular elements 
tf = isInterior(dt) ;
% get points and nodes 
p = dt.Points ;
t = dt.ConnectivityList ;
% Pick the required 
t(~tf,:) = [] ;
% Make deluanay again 
dt = triangulation(t,p);   
triplot(dt)

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Holden Tranquillo 2022-3-5

编辑：KSSV 2022-3-7

在 MATLAB Online 中打开

The issue was in the way the variable 'id' was found. I have done it a different way. Please load the perimeters and then run the attached code if you can. It seems like the triangulations get shifted a little bit even though they seem accurate (if you compare the two plots you can see the difference)

%% Colorful Contours
col_list='ymcrgbk';
figure();
for i = 1:9
    
    col=randi([1,7],1);
    random_color=col_list(col);    
    final_color=['-' random_color];
    
    var = eval(append('perimeter',num2str(i)));
    contour = patch(gca,var(:,1),var(:,2),final_color);
    hold on;
    rotate(contour,[0 0 1],270);
end
%% STL Write
p = [perimeter1 ; perimeter2 ; perimeter3 ; perimeter4 ; perimeter5 ; perimeter6 ; perimeter7 ; perimeter8 ;
    perimeter9] ;
col_list='ymcrgbk';
% Create STL's of Each Contour
for i = 1:9
    
    filename = convertCharsToStrings(append('perimeter',num2str(i)));
    temp = eval(filename);
    %  temp = perimeter2;
    
    %id = knnsearch(p,temp) ; 
    id = linspace(1,length(temp),length(temp))';
    C = [id(1:end-1) id(2:end)]; 
    % Make delaunay triangulation with constraints
    dt = delaunayTriangulation(temp,C) ;
    % Get the interior triangular elements 
    tf = isInterior(dt) ;
    % get points and nodes 
    points = dt.Points ;
    t = dt.ConnectivityList ;
    % Pick the required 
    t(~tf,:) = [] ; % only save elements of interior triangles
    % Make deluanay again 
    dt = triangulation(t,points);
    % Plot
    col=randi([1,7],1);
    random_color=col_list(col);    
    final_color=['-' random_color];
    tri = triplot(dt,final_color);
    rotate(tri,[0 0 1],270);
    axis equal
    hold on;
    
end

KSSV 2022-3-7

在 MATLAB Online 中打开

Using perimeter2 doesnot crash my MATLAB. You may consider using like shown below:

id = knnsearch(perimeter2,perimeter2) ; 
C = [id(1:end-1) id(2:end)]; 
% Make delaunay triangulation with constriants 
dt = delaunayTriangulation(perimeter2,C) ;
% Get the interior triangular elements 
tf = isInterior(dt) ;
% get points and nodes 
p = dt.Points ;
t = dt.ConnectivityList ;
% Pick the required 
t(~tf,:) = [] ;
% Make deluanay again 
dt = triangulation(t,p);   
triplot(dt)

Holden Tranquillo 2022-4-7

Hi KSSV, sorry to bother you again, but there is on emore thing I cannot seem to figure out. I am now using a filter on the boundary traces in order to smooth them out, and now during the STL creation, the 'isInterior' command returns all true, and thus the correct STLs are not being created. If you can, can you glance at this attached code and see if you can figure out why it returns all true? I cannot figure it out

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