obj2stl.py

#!/usr/bin/env python
obj = open('surface.obj')
_, _, _, _, _, _, np = obj.readline().strip().split()
np = int(np)
vertices=[]
normals=[]
triangles=[]

# np vertices as (x,y,z)
min_x, min_y, min_z = 0, 0, 0
for i in range(np):
  x, y, z = map(float,obj.readline().strip().split()) 
  min_x, min_y, min_z = min(x,min_x), min(y,min_y), min(z,min_z)
  vertices.append((x, y, z))
# move object to the positive quadrant
for i in range(np): 
  x,y,z = vertices[i]
  vertices[i] = (x-min_x,y-min_y,z-min_z)

assert obj.readline().strip() == ""
# np normals as (x,y,z)
for i in range(np):
  normals.append(tuple(map(float,obj.readline().strip().split())))

assert obj.readline().strip() == ""
nt=int(obj.readline().strip().split()[0]) # number of triangles
_, _, _, _, _ = obj.readline().strip().split()
assert obj.readline().strip() == ""
# rest of the file is a list of numbers
points = map(int, "".join(obj.readlines()).strip().split())
points = points[nt:]  # ignore these.. (whatever they are)
for i in range(nt): 
  triangles.append((points.pop(0), points.pop(0), points.pop(0)))

print "solid surface"
for triangle in triangles: 
  x1, y1, z1 = vertices[triangle[0]]
  x2, y2, z2 = vertices[triangle[1]]
  x3, y3, z3 = vertices[triangle[2]]
  # normal = (v2 - v1)x(p3-p1)
  # normal = (  (y2-y1)*(z3-z1)-(y3-y1)*(z2-z1), 
  #            (z2-z1)*(x3-x1)-(x2-x1)*(z3-z1), 
  #            (x2-x1)*(y3-y1)-(x2-x1)*(y2-y1) )
  print "\tfacet normal {0} {1} {2}".format(0, 0, 0)
  print "\t\tvertex {0:e} {1:e} {2:e}".format(x1, y1, z1)
  print "\t\tvertex {0:e} {1:e} {2:e}".format(x2, y2, z2)
  print "\t\tvertex {0:e} {1:e} {2:e}".format(x3, y3, z3)
  print "\tendloop"
print "endfacet"