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ifcopenshell.util.boundary: make face matrix robust against collinear first vertices

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_face_matrix_from_verts used only the first 3 vertices and sb.np_normal, which divides by zero when they are collinear. Triangulated meshes from generated spaces often start with collinear boundary vertices, producing NaN matrices and a shapely LinearRing error. Walk the polygon to find a non-degenerate normal and edge.

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CyrilWaechter
2026-08-02 06:48:36 +02:00
parent c8f8196b09
commit adf01be1d0
1 changed files with 24 additions and 6 deletions
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src/ifcopenshell-python/ifcopenshell/util/boundary.py
+24 -6
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@@ -261,7 +261,7 @@ def auto_generate_boundaries(
) )
space_face_normal_world = space_matrix_3x3 @ space_face_normal_local space_face_normal_world = space_matrix_3x3 @ space_face_normal_local
face_matrix = _face_matrix_from_verts(space_verts_l[:3]) face_matrix = _face_matrix_from_verts(space_verts_l)
face_matrix_inv = np.linalg.inv(face_matrix) face_matrix_inv = np.linalg.inv(face_matrix)
space_face_polygon = _verts_to_polygon(space_verts_l, face_matrix_inv, snap=1e-6) space_face_polygon = _verts_to_polygon(space_verts_l, face_matrix_inv, snap=1e-6)
if not space_face_polygon.is_valid: if not space_face_polygon.is_valid:
@@ -870,11 +870,29 @@ def _face_normal(verts: np.ndarray) -> Optional[np.ndarray]:
def _face_matrix_from_verts(verts3: np.ndarray) -> np.ndarray: def _face_matrix_from_verts(verts3: np.ndarray) -> np.ndarray:
"""Build a 4x4 face-local coordinate matrix from 3 vertices.""" """Build a 4x4 face-local coordinate matrix from a polygon's vertices.
p1, p2, p3 = verts3[0], verts3[1], verts3[2]
z = sb.np_normal([p1, p2, p3]) The first three vertices may be collinear in triangulated meshes, so the
x = sb.np_normalized(p2 - p1) normal is computed from the first non-degenerate triple and the X axis is
return ifcopenshell.util.placement.a2p(o=p1, z=z, x=x) taken from the first non-degenerate edge.
"""
p1 = np.asarray(verts3[0])
normal = _face_normal(verts3)
if normal is None:
raise ValueError("Cannot build face matrix from a degenerate polygon")
x = np.zeros(3)
for i in range(len(verts3) - 1):
edge = np.asarray(verts3[i + 1]) - np.asarray(verts3[i])
edge_norm = np.linalg.norm(edge)
if edge_norm > 1e-8:
x = edge / edge_norm
break
if np.linalg.norm(x) < 1e-8:
raise ValueError("Cannot find a non-degenerate edge for the face matrix")
return ifcopenshell.util.placement.a2p(o=p1, z=normal, x=x)
def _verts_to_polygon(verts: np.ndarray, face_matrix_inv: np.ndarray, snap: float = 0) -> shapely.Polygon: def _verts_to_polygon(verts: np.ndarray, face_matrix_inv: np.ndarray, snap: float = 0) -> shapely.Polygon: