# File: stlwrite.py
# Purpose: Export 3D objects built of faces with 3 or 4 vertices, as
# an ASCII or Binary STL file.
# License: MIT License
#
# Original source from http://code.activestate.com/recipes/578246-stl-writer/
# Modified by David Touretzky, November 2014, to compute surface normals.
import math
import struct
ASCII_FACET = """facet normal {normal[0]:.4f} {normal[1]:.4f} {normal[2]:.4f}
outer loop
vertex {face[0][0]:.4f} {face[0][1]:.4f} {face[0][2]:.4f}
vertex {face[1][0]:.4f} {face[1][1]:.4f} {face[1][2]:.4f}
vertex {face[2][0]:.4f} {face[2][1]:.4f} {face[2][2]:.4f}
endloop
endfacet
"""
BINARY_HEADER ="80sI"
BINARY_FACET = "12fH"
def crossproduct(u,v):
 s1 = u[1]*v[2] - u[2]*v[1]
 s2 = u[2]*v[0] - u[0]*v[2]
 s3 = u[0]*v[1] - u[1]*v[0]
 return [s1, s2, s3]
def norm(v):
 return math.sqrt(v[0]*v[0] + v[1]*v[1] + v[2]*v[2])
def normalize(v):
 m = norm(v)
 if m == 0:
 m = 1
 return [v[0]/m, v[1]/m, v[2]/m]
def normalto(u,v):
 return normalize(crossproduct(u,v))
def diff(u,v):
 return [u[0]-v[0], u[1]-v[1], u[2]-v[2]]
class ASCII_STL_Writer:
 """ Export 3D objects build of 3 or 4 vertices as ASCII STL file.
 """
 def __init__(self, stream):
 self.fp = stream
 self._write_header()
 def _write_header(self):
 self.fp.write(b"solid python\n")
 def close(self):
 self.fp.write(b"endsolid python\n")
 def _write(self, face):
 n = normalto(diff(face[0],face[1]),diff(face[1],face[2]))
 self.fp.write(bytes(ASCII_FACET.format(normal=n,face=face),'utf8'))
 def _split(self, face):
 p1, p2, p3, p4 = face
 return (p1, p2, p3), (p3, p4, p1)
 def add_face(self, face):
 """ Add one face with 3 or 4 vertices. """
 if len(face) == 4:
 face1, face2 = self._split(face)
 self._write(face1)
 self._write(face2)
 elif len(face) == 3:
 self._write(face)
 else:
 raise ValueError('only 3 or 4 vertices for each face')
 def add_faces(self, faces):
 """ Add many faces. """
 for face in faces:
 self.add_face(face)
class Binary_STL_Writer(ASCII_STL_Writer):
 """ Export 3D objects build of 3 or 4 vertices as binary STL file.
 """
 def __init__(self, stream):
 self.counter = 0
 ASCII_STL_Writer.__init__(self,stream)
 def close(self):
 self._write_header()
 def _write_header(self):
 self.fp.seek(0)
 self.fp.write(struct.pack(BINARY_HEADER, b'Python Binary STL Writer', self.counter))
 def _write(self, face):
 self.counter += 1
 n = normalto(diff(face[0],face[1]),diff(face[1],face[2]))
 data = [
 n[0], n[1], n[2],
 face[0][0], face[0][1], face[0][2],
 face[1][0], face[1][1], face[1][2],
 face[2][0], face[2][1], face[2][2],
 0
 ]
 self.fp.write(struct.pack(BINARY_FACET, *data))
def example():
 def get_triangles():
 p1 = (0, 0, 0)
 p2 = (1, 2, 3)
 p3 = (-5, -7, 4)
 p4 = (3, -2, 6)
 return [ [p1, p3, p2], [p2, p3, p4], [p4, p3, p1], [p4, p1, p2] ]
 filename = 'triangles.stl'
 with open(filename, 'wb') as fp:
 writer = ASCII_STL_Writer(fp)
 writer.add_faces(get_triangles())
 writer.close()
 print('Wrote ' + filename)
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