failed area calculation due to normals coming back as direction vectors

[NicoAraujo80]

When calculating the area in base.py file def update_areas(self): areas = .5 * numpy.sqrt((self.normals ** 2).sum(axis=1)) self.areas = areas.reshape((areas.size, 1)) self.normals all have magnitudes of one causing areas to be equal to half the amount of triangles in the stl file

The code I used to test this after seeing that a calculation I was making was off was: from stl import mesh stlObject = mesh.Mesh.from_file('40mmcube.stl') stlObject.update_areas() area = stlObject.areas.sum()

with the area coming back as 6. There are 12 normals 4 pointing in the x, y, and z axis all with a magnitude of 1. I'm assuming that for the area to be calculated properly the normals have a magnitude equal to the area of that triangle. Though I was not able to track down where the normals get calculated.

[wolph]

I created a new versions 4 days ago that fixed this, I think you might be using the older version :) https://github.com/WoLpH/numpy-stl/issues/122

[NicoAraujo80]

Your right. I had seen that issue and had uninstalled the package and reinstalled it with pip, but the problem still persisted. I thought it wasn't fully fixed.

[wolph]

As far as I can see it's working properly. Generating half a cube with sides size 1 I get 3 as expected:

from stl import mesh
import numpy

# Create 3 faces of a cube
data = numpy.zeros(6, dtype=mesh.Mesh.dtype)

# Top of the cube
data['vectors'][0] = numpy.array([[0, 1, 1],
                                    [1, 0, 1],
                                    [0, 0, 1]])
data['vectors'][1] = numpy.array([[1, 0, 1],
                                    [0, 1, 1],
                                    [1, 1, 1]])
# Front face
data['vectors'][2] = numpy.array([[1, 0, 0],
                                    [1, 0, 1],
                                    [1, 1, 0]])
data['vectors'][3] = numpy.array([[1, 1, 1],
                                    [1, 0, 1],
                                    [1, 1, 0]])
# Left face
data['vectors'][4] = numpy.array([[0, 0, 0],
                                    [1, 0, 0],
                                    [1, 0, 1]])
data['vectors'][5] = numpy.array([[0, 0, 0],
                                    [0, 0, 1],
                                    [1, 0, 1]])

half_cube = mesh.Mesh(data.copy())
print(half_cube.areas.sum())
# returns 3

[NicoAraujo80]

Yea it works now because I manually changed the files. I don't know much about pip but it doesn't seem to be installing the commit from 4 days ago which solved this problem.

[wolph]

you're right, looks like something went wrong with the release

I'll create a new release

On Tue, 31 Mar 2020, 21:03 NicoAraujo80, notifications@github.com wrote:

Yea it works now because I manually changed the files. I don't know much about pip but it doesn't seem to be installing the commit from 4 days ago which solved this problem.

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[wolph]

Thanks for letting me know the release failed :)

[NicoAraujo80]

No problem, glad I could help