Issue with 'difference' Function - Incorrect Object Removal and Polygon Closure

[Tommamgo]

Hello,

I hope you're doing well. I've come across an issue while testing the 'difference' function. During the process of subtracting an STL file from another, I observed that while the object's orientation was correctly subtracted, the polygons were not closed properly.

Code:

from madcad import *

#open
read_mesh1 = io.read("stl1.stl")
read_mesh2 = io.read("stl2.stl")
read_mesh1.mergeclose()
read_mesh2.mergeclose()


# Remove the volume of the second to the first
diff = difference(read_mesh2, read_mesh1)

# Write
io.write(diff, "mesh.stl")

Result:

This should be the Result:

stl1 and stl2:

stl.zip

[jimy-byerley]

I cannot reproduce the issue on my side with the master branch
Which version of pymadcad do you use ?

[Tommamgo]

Thank you for the prompt response.

Unfortunately, I had already deleted the library. With the understanding that it could have been due to an incorrect version of the library, I tried again with the same code example and the library version.

This time, I didn't encounter any faulty output files.

However, this time I faced issues with different test .stl files:

Traceback (most recent call last):
File "/home/linus/PycharmProjects/madCAD/main.py", line 30, in
diff = difference(read_mesh2, read_mesh1)
File "/home/linus/anaconda3/envs/madCAD/lib/python3.10/site-packages/madcad/boolean.py", line 638, in difference
return boolean(a,b, (False,True))
File "/home/linus/anaconda3/envs/madCAD/lib/python3.10/site-packages/madcad/boolean.py", line 620, in boolean
return op(a, b, sides, prec)
File "/home/linus/anaconda3/envs/madCAD/lib/python3.10/site-packages/madcad/boolean.py", line 254, in boolean_mesh
mc1 = pierce_mesh(m1, m2, sides[0], prec)
File "/home/linus/anaconda3/envs/madCAD/lib/python3.10/site-packages/madcad/boolean.py", line 166, in pierce_mesh
m1, frontier = cut_mesh(m1, m2, prec)
File "/home/linus/anaconda3/envs/madCAD/lib/python3.10/site-packages/madcad/boolean.py", line 147, in cut_mesh
flat = triangulation.triangulation_closest(segts, normal, prec)
File "/home/linus/anaconda3/envs/madCAD/lib/python3.10/site-packages/madcad/triangulation.py", line 759, in triangulation_closest
result += triangulation_outline(loop, z, prec)
File "/home/linus/anaconda3/envs/madCAD/lib/python3.10/site-packages/madcad/triangulation.py", line 294, in triangulation_outline
raise TriangulationError("no more feasible triangles (algorithm failure or bad input outline)", [outline.indices[i] for i in hole])
madcad.triangulation.TriangulationError: ('no more feasible triangles (algorithm failure or bad input outline)', [120, 127, 125, 92])

I used these two .stl files:
files.zip

System:
Date: Wed Aug 30 18:20:02 2023 CEST

            OS : Linux
        CPU(s) : 4
       Machine : x86_64
  Architecture : 64bit
   Environment : Python
   GPU Details : error

MathText Support : False

PIP:
appdirs==1.4.4
arrex==0.5.2
blessed==1.19.1
distlib==0.3.7
flyingcircus==0.1.4.0
glcontext==2.4.0
Jinja2==3.1.2
MarkupSafe==2.1.3
moderngl==5.8.2
nose==1.3.7
numpy==1.25.2
numpy-stl==3.0.1
packaging==21.3
Pillow==10.0.0
plyfile==1.0.1
PyGLM==2.7.0
pymadcad==0.15.1
pynsist==2.8
PyQt5==5.15.9
PyQt5-Qt5==5.15.2
PyQt5-sip==12.12.2
pyserial==3.5
python-utils==3.7.0
pytk==0.0.2.1
PyWavefront==1.3.3
PyYAML==6.0.1
requests_download==0.1.2
scipy==1.11.2
setuptools-scm==6.4.2
tomli==2.0.1
typing_extensions==4.7.1
wcwidth==0.2.5
yarg==0.1.9

from madcad import *

#open
read_mesh1 = io.read("stl1.stl")
read_mesh2 = io.read("stl2.stl")
read_mesh1.mergeclose()
read_mesh2.mergeclose()


# Remove the volume of the second to the first
diff = difference(read_mesh2, read_mesh1)

# Write
io.write(diff, "mesh.stl")

Did I do something wrong in my setup?

Thank you.

[jimy-byerley]

This discussion should be a different issue then

I don't know exactly what is stl1.stl and stl2.stl in your example since your zip file only contains Basis.stl and Gemin.stl
However that seems to be a floating point precision issue: I could avoid the problem with a slight shift of one of your meshes

difference(basis, gemein.transform(0.001*vec3(1)))

[Tommamgo]

Thank you for the quick response.

I apologize for the incorrect file naming.

stl1.stl = Basis.stl
stl2.stl = Gemin.stl

With your changes, I was able to compile it and achieved the desired results.

Thanks!

[jimy-byerley]

Happy that it worked for you !
I will keep this issue opened since the floating point precision issue is a bug that needs to be solved
Thanks for reporting