converted normals to unit vectors to fix #108

wolph · Aug 7, 2019 · dcbe8cd · dcbe8cd
1 parent 87101f8
commit dcbe8cd
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Showing 2 changed files with 10 additions and 4 deletions.
diff --git a/stl/base.py b/stl/base.py
@@ -315,7 +315,11 @@ def remove_empty_areas(cls, data):
 
     def update_normals(self):
         '''Update the normals for all points'''
-        self.normals[:] = numpy.cross(self.v1 - self.v0, self.v2 - self.v0)
+        normals = numpy.cross(self.v1 - self.v0, self.v2 - self.v0)
+        normal = numpy.linalg.norm(normals)
+        if normal:
+            normals /= normal
+        self.normals[:] = normals
 
     def update_min(self):
         self._min = self.vectors.min(axis=(0, 1))

diff --git a/tests/test_mesh.py b/tests/test_mesh.py
@@ -33,8 +33,10 @@ def test_units_2d():
     mesh = Mesh(data, remove_empty_areas=False)
     mesh.update_units()
 
-    assert numpy.allclose(mesh.areas, [.5, .5])
-    assert numpy.allclose(mesh.normals, [[0, 0, 1.], [0, 0, -1.]])
+    assert numpy.allclose(mesh.areas, [0.35355338, 0.35355338])
+    assert numpy.allclose(mesh.normals, [
+                          [0.0, 0.0, 0.70710677],
+                          [0.0, 0.0, -0.70710677]])
     assert numpy.allclose(mesh.units, [[0, 0, 1], [0, 0, -1]])
 
 
@@ -48,7 +50,7 @@ def test_units_3d():
     mesh.update_units()
 
     assert (mesh.areas - 2 ** .5) < 0.0001
-    assert numpy.allclose(mesh.normals, [0, -1, 1])
+    assert numpy.allclose(mesh.normals, [0.0, -0.70710677, 0.70710677])
 
     units = mesh.units[0]
     assert units[0] == 0