fix(face): Fix issue with duplicate Face3D vertices and tolerance

It seems that duplicate vertices with coordinate differences very close to Python floating point tolerance can cause the normal calculation to go haywire.  I am changing the normal calculation to ignore any vertices that are closer than a value that's a bit larger than floating point tolerance (1e-9) rather than using a ZeroDivisionError indicating a perfectly duplicate vertex.

I also realized that the remove_colinear_vertices method can accidentally remove both versions of a duplicate vertex, which is usually not the desired behavior as we want to leave one of them. I'm tweaking the method so that it corrects itself whenever it has already removed colinear vertices.

ladybug_geometry/geometry3d/face.py

@@ -704,7 +704,7 @@ def remove_colinear_vertices(self, tolerance):
             return self
         if not self.has_holes:  # we only need to evaluate one list of vertices
             new_vertices = self._remove_colinear(
-            self._vertices, self.polygon2d, tolerance)
+                self._vertices, self.polygon2d, tolerance)
             _new_face = Face3D(new_vertices, self.plane, enforce_right_hand=False)
             return _new_face
         # the face has holes
@@ -1738,11 +1738,15 @@ def _remove_colinear(self, pts_3d, pts_2d, tolerance):
         triangle formed by 3 vertices is less than the tolerance.
         """
         new_vertices = []
+        skip = 0
         for i, _v in enumerate(pts_2d):
-            _a = pts_2d[i - 2].determinant(pts_2d[i - 1]) + \
-                pts_2d[i - 1].determinant(_v) + _v.determinant(pts_2d[i - 2])
+            _a = pts_2d[i - 2 - skip].determinant(pts_2d[i - 1]) + \
+                pts_2d[i - 1].determinant(_v) + _v.determinant(pts_2d[i - 2 - skip])
             if abs(_a) >= tolerance:
                 new_vertices.append(pts_3d[i - 1])
+                skip = 0
+            else:
+                skip += 1
         return new_vertices
 
     def _is_sub_face(self, face):
@@ -1913,6 +1917,7 @@ def _plane_from_vertices(verts):
             normal = [x1 + x2, y1 + y2, z1 + z2]
             # walk around the whole shape to avoid colinear vertices
             for i in range(len(verts) - 2):
+                tri_verts = verts[i:i + 3]
                 x, y, z = Face3D._normal_from_3pts(*verts[i:i + 3])
                 normal[0] += x
                 normal[1] += y
@@ -1936,11 +1941,10 @@ def _normal_from_3pts(pt1, pt2, pt3):
         # normalize the vectors to make them unit vectors
         d1 = math.sqrt(v1[0] ** 2 + v1[1] ** 2 + v1[2] ** 2)
         d2 = math.sqrt(v2[0] ** 2 + v2[1] ** 2 + v2[2] ** 2)
-        try:
-            v1 = (v1[0] / d1, v1[1] / d1, v1[2] / d1)
-            v2 = (v2[0] / d2, v2[1] / d2, v2[2] / d2)
-        except ZeroDivisionError:  # duplicate vertices in triplet
+        if d1 < 1e-9 or d2 < 1e-9:  # effectively duplicate vertices in triplet
             return (0, 0, 0)
+        v1 = (v1[0] / d1, v1[1] / d1, v1[2] / d1)
+        v2 = (v2[0] / d2, v2[1] / d2, v2[2] / d2)
         # return the cross product
         return (v1[1] * v2[2] - v1[2] * v2[1],
                 -v1[0] * v2[2] + v1[2] * v2[0],

tests/face3d_test.py

@@ -602,6 +602,19 @@ def test_remove_colinear_vertices():
     assert len(face_2.remove_colinear_vertices(0.0001).vertices) == 4
 
 
+def test_remove_colinear_vertices_custom():
+    """Test the remove_colinear_vertices method with some custom geometry."""
+    geo_file = './tests/json/dup_vert_face.json'
+    with open(geo_file, 'r') as fp:
+        geo_dict = json.load(fp)
+    face_geo = Face3D.from_dict(geo_dict)
+
+    assert -1e-3 < face_geo.normal.z < 1e-3
+    assert len(face_geo.vertices) == 17
+
+    assert len(face_geo.remove_colinear_vertices(0.0001).vertices) == 16
+
+
 def test_triangulated_mesh_and_centroid():
     """Test the triangulation properties of Face3D."""
     pts_1 = (Point3D(0, 0, 2), Point3D(2, 0, 2), Point3D(2, 2, 2), Point3D(0, 2, 2))

tests/json/dup_vert_face.json

@@ -0,0 +1,90 @@
+{
+    "type": "Face3D", 
+    "boundary": [
+        [
+            -32.921611201331253, 
+            -412.66628343081106, 
+            1.5082130414885986
+        ], 
+        [
+            -32.92161450752139, 
+            -412.66628142228097, 
+            0.79654637483244661
+        ], 
+        [
+            -33.537845196710784, 
+            -413.8757310807286, 
+            0.79654582428383403
+        ], 
+        [
+            -33.537842348260362, 
+            -413.8757221976216, 
+            -0.0047076652449124547
+        ], 
+        [
+            -22.359531583272815, 
+            -391.95842979489032, 
+            -0.0044249400893101778
+        ], 
+        [
+            -22.359554793487792, 
+            -391.95850217769248, 
+            6.5244813094684488
+        ], 
+        [
+            -33.537865558475346, 
+            -413.87579458042376, 
+            6.5241985843128463
+        ], 
+        [
+            -33.537858287046141, 
+            -413.8757719039246, 
+            4.4787854075706282
+        ], 
+        [
+            -32.921597400939412, 
+            -412.66629181463094, 
+            4.4787859581113754
+        ], 
+        [
+            -32.921600013420004, 
+            -412.66629022753347, 
+            3.9164422081196832
+        ], 
+        [
+            -33.537856287918139, 
+            -413.87576566949343, 
+            3.9164416575777357
+        ], 
+        [
+            -33.537858044533692, 
+            -413.87576395490083, 
+            3.8528999909160246
+        ], 
+        [
+            -32.921600308615552, 
+            -412.66629004820044, 
+            3.8529005414539577
+        ], 
+        [
+            -32.921610906135705, 
+            -412.66628361014409, 
+            1.5717547081543268
+        ], 
+        [
+            -32.921610906135712, 
+            -412.66628361014409, 
+            1.5717547081543268
+        ], 
+        [
+            -33.537857160655768, 
+            -413.87573498333205, 
+            1.5717541576266509
+        ], 
+        [
+            -33.537847726680695, 
+            -413.87573897063021, 
+            1.5082124909415064
+        ]
+    ]
+}