# I have 2D .jpg images which I want to convert into 3D.stl files with same thickness throughout (eg two Z values) in the created .stl file

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AARISH NAWAZ on 21 Jan 2022
Answered: yanqi liu on 22 Jan 2022
1)I already have a code which converts a 2D .jpg (MATLAB_Example.jpg) image into a 2D .stl file (MATLAB_ANSWERS_IMG2STL_EXACT.m) but when I open this .stl file created by the code in 3D printing software like cura i am not able extrude the z axis since its a single layer of x(i),y(i) points. I would really appreciate if someone can guide me on what approach is needed in order to add another layer with same x y coordinates but a new Z (for the third dimension)?
% parameters
prescale = 0.1; % this scales the contours prior to simplification
% transform the image into binary
A = ~imbinarize(rgb2gray(A));
A = bwareafilt(A,1);
% rotate coordinate
A = fliplr(A.');
% get the contours of the image
% find boundary
bnd = bwboundaries(A);
% parse the contours
for i=1:length(bnd)
bnd_tmp = bnd{i};
assert(all(bnd_tmp(1,:)==bnd_tmp(end,:)), 'contour is not closed')
c_cell{i} = prescale.*bnd_tmp;
end
% create the 2d triangulation
% for each contour, prepare the polygons
for i=1:length(c_cell)
c_tmp = c_cell{i};
x_vec{i} = c_tmp(:,1).';
y_vec{i} = c_tmp(:,2).';
end
% get the polygon and make the triangulation
poly = polyshape(x_vec, y_vec, 'Simplify', false);
tr = triangulation(poly);
triplot(tr)
axis equal % write to stl
stlwrite(tr,'mything.stl','text')
end of 1st part
2)I tried it with alphaShape functionand gave two values for Z(1 and -1) in the (MATLAB_ANSWERS_IMG2STL_3D.m) code and I was able to obtain the 3D structure (with same thickness in the entire structure as i need) but it does not look like the .jpg input image (there is something which is wrong with the code)
% transform the image into binary
A = ~imbinarize(rgb2gray(A));
A = bwareafilt(A,1);
% rotate coordinate
A = fliplr(A.');
% get the contours of the image
% find boundary
bnd = bwboundaries(A);
% parse the contours
for i=1:length(bnd)
bnd_tmp = bnd{i};
assert(all(bnd_tmp(1,:)==bnd_tmp(end,:)), 'contour is not closed')
c_cell{i} = prescale.*bnd_tmp;
end
% create the 2d triangulation
% for each contour, prepare the polygons
for i=1:length(c_cell)
c_tmp = c_cell{i};
x_vec{i} = c_tmp(:,1).';
y_vec{i} = c_tmp(:,2).';
end
% get the polygon and make the triangulation
for i=1:size(x_vec,2)
polyXYZsecond{i} =[x_vec{i}.', y_vec{i}.',-ones(1,size(x_vec{i},2)).'];
polyXYZfirst{i} =[x_vec{i}.', y_vec{i}.',ones(1,size(x_vec{i},2)).'];
end
allXYZcell=[polyXYZfirst,polyXYZsecond];
for i=1:2*size(x_vec,2)
polyXall{i}=allXYZcell{1,i}(1:end,1);
end
for i=1:2*size(x_vec,2)
polyYall{i}=allXYZcell{1,i}(1:end,2);
end
for i=1:2*size(x_vec,2)
polyZall{i}=allXYZcell{1,i}(1:end,3);
end
Xallvalues= cat(1, polyXall{:});
Yallvalues= cat(1, polyYall{:});
Zallvalues= cat(1, polyZall{:});
XYZ=[Xallvalues,Yallvalues,Zallvalues];
poly=alphaShape(XYZ)
Warning: Duplicate data points have been detected and removed.
poly =
alphaShape with properties: Points: [9268×3 double] Alpha: 4.0566 HoleThreshold: 0 RegionThreshold: 0
[bf, P] = boundaryFacets(poly);
TR=triangulation(bf,P)
TR =
triangulation with properties: Points: [9268×3 double] ConnectivityList: [18540×3 double]
triplot(TR)
axis equal stlwrite(TR,'mything.stl','text')
I would really appreciate if someone can help me with this issue. (Please see the attachments for clarity)

yanqi liu on 22 Jan 2022
yes，sir，may be use
f is Faces，v is Vertices
tr2 = triangulation(f,v);
stlwrite(tr2,'demo.stl');