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def mkStlInertial(stlFileName, verbose=False):
'''Maps a stl mesh into one of its inertial frame. The new .stl will be saved, appending '_madeI.stl' to *stlFileName*. Requires stl Python module, see https://pypi.org/project/numpy-stl/.
:stlFileName: path to the .stl to consider, wo the .stl extension (string)
:verbose: boolean to control informative message outputs about the function process
'''
import numpy, time
try:
import stl # = https://pypi.org/project/numpy-stl/. Alternate choice https://python-stl.readthedocs.io/en/latest/ is no longer maintained on https://github.com/apparentlymart/python-stl
except ModuleNotFoundError: # using except just for a print, not really avoiding the error
print('****Python module stl is required, see the doc****')
import stl # we still repeat the same command for the error to appear to the user
t1 = time.time()
stlMesh = stl.mesh.Mesh.from_file(stlFileName + '.stl')
t2 = time.time()
if verbose:
print('\nReading given file in', t2 - t1, 'seconds')
volume, cog, inertia = stlMesh.get_mass_properties() # cog being a numpy array
t1 = time.time()
if verbose:
print('Computing mass properties in ~', t1 - t2, 'seconds')
print('Initially, stl is centered at', cog, 'with inertia\n', inertia)
# Getting eigenbasis information:
[val, vect] = numpy.linalg.eig(inertia) # vect is the eigenvectors basis in current basis
if numpy.linalg.det(vect) < 0: # eg (x,z,y)
if verbose:
print('Non right-handed basis, modifying vect, which is for now\n', vect)
vect[:, 2] = -vect[:, 2] # making it (x,z,-y) which is a more suitable basis
if verbose:
print('And now\n', vect, '\nwith determinant', numpy.linalg.det(vect))
rot = vect.T # taking the transpose that will be useful for changing basis
# Applying the transformation, avoiding to use eg stlMesh.transform or stlMesh.rotate on purpose (with source code at https://github.com/WoLpH/numpy-stl/tree/develop/stl/base.py) because of https://github.com/WoLpH/numpy-stl/issues/166:
for fIdx in range(len(stlMesh.vectors)): # loop over facets
for vIdx in range(3): # loop over 3 vertices in each facet
stlMesh.vectors[fIdx][vIdx] = rot @ (stlMesh.vectors[fIdx][vIdx] - cog)
if verbose:
volume, cog, inertia = stlMesh.get_mass_properties()
print('\nAfter transformation, stl is centered at', cog, 'and has following inertia\n', inertia)
stlMesh.save(stlFileName + '_madeI.stl')
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