Help with using scanf and editing a txt file?

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Taylor Gates
Taylor Gates 2018-7-20
编辑： Guillaume 2018-7-20
I'm trying to modify an stl file to eventually 3D print. I am trying to take out the bottom half of the object by using matlab. Essentially, I converted the stl file to .txt so I can analyze the z values to cut away the bottom half. I am trying to use the scanf function or something like it to read the vertices of the triangles, find max and min of xyz, and delete triangles if z<(zmax+zmin)/2. How can I accomplish this?
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Guillaume
Guillaume 2018-7-20
Assuming that we have code to read the vertices (it's not too hard to write that efficiently) that produces for example a Nfacet x Nvertices x 3 matrix. How do you decide which facets to remove? Mathematically.
Taylor Gates
Taylor Gates 2018-7-20
I'm pretty new to matlab and programming so I am still working on a code to read the vertices. Do you have any guidance towards that?

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Guillaume
Guillaume 2018-7-20
编辑：Guillaume 2018-7-20
This is how I'd read all the vertices.
%assumptions:
% all vertices are made of 3 coordinates
% all faces are made of 3 vertices
%the code completely ignore the non-vertex lines
lines = strsplit(fileread('thinker.txt'), \n'); %read whole file and split into lines
vertlines = strjoin(lines(startsWith(lines, 'vertex')), '\n'); %identify vertex lines and rejoin
vertices = reshape(sscanf(vertlines, 'vertex %f%f%f\n'), 3, 3, []); %read vertices coordinates and reshape into something useful
This will give you a 3 x Nvertex x Nfacet matrix.
As you've not explained what filtering you want to do after that, I can't help you further.
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Taylor Gates
Taylor Gates 2018-7-20
Thank you. So should I come up with a max allowable z value to input to filter out all the others. Essentially I am just trying to cut away the bottom half of the image and I know that will be done through the z values. So would I come up with a range of acceptable z values?

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