Translate the origin of a STL file

I need to translate the origine of an STL. What I tried to do is to open the stl with the readstl script I found on the file exange. then I used reshape to do a 3 by n matrix with the cordinate:

X=reshape(coordinates, 3, [])';

Then I tooke of the offset I want to each point:

Y(i,:)=X(i,:)-Offset;

And generate a new STL from it with the stlwrite script also from the file exange.

stlwrite(strcat(input('Nom du fichier :','s'),'.stl'), Y(:, 1)', Y(:, 2)', Y(:, 3)', 'mode', 'ascii');

The problem I get is that when it build up the new stl is that the vertexes are in the good position according to the new origin but the facet are build "randomly" between any vertexes. (not randomly because it seems to build each time the same facet but not generate the same surface than the original file.)

I would really appreciate any help or advice about improving the my code or an other soft where it it is easier to translate the origin.

Thanks you all in advance.

readSTL: http://www.mathworks.com/matlabcentral/fileexchange/41910-function-for-importing-and-plotting-stl-files-in-matlab/content/readSTL.m

stlwrite: http://www.mathworks.com/matlabcentral/fileexchange/20922-stlwrite-write-binary-or-ascii-stl-file

[Sean de Wolski]

Can you post the code you're using to do the offset start to finish?

[Pierrick Bersier]

Here is the script with the two STL I used. The aim was to place the origin at the center off the femoral head. I tooke the coordinated of it using a stl fil that I cut off and let only the join head on it and then with the spherefit.

spherefit:

http://www.mathworks.com/matlabcentral/fileexchange/34129-sphere-fit--least-squared-

Answer 1

[Sean de Wolski]

Your logic and algorithm implementation look correct to me. I believe the problem is coming from the way you import the STL file. Instead of using that function, use one of the ones from the FEX that gives you an option to read it in as faces and vertices. E.g.

http://www.mathworks.com/matlabcentral/fileexchange/30923-fast-stl-import-function

From here, repeat your centroid calculation and subtraction on the vertices component and then write it back out using the same faces and the modified vertices. The reason for the behavior you are seeing is because stlwrite is trying to connect the x/y/z data because it does not know the faces. A reader that gives you faces allows you it to skip this step.

[Pierrick Bersier]

Thank you a lot for your help. I try to use the script you advice me but when I do I get this error:

Subscript indices must either be real positive integers or logicals.

Error in import_stl_fast (line 59) if (C{4}(end)== NaN)

Any Idea?

[Sean de Wolski]

I don't know. There are other readers too, just make sure you find one with faces/vertices as an output option.

[Pierrick Bersier]

Thanks you a lot one more time ! I finally get it to work ! You are awesome, I never expected such a fast answer !

[Irene Yang]

Sorry to bring this up again since it has been many years - but may I please ask what you did to solve this problem exactly? I have the same issue and when I tried the code, it didn't work.