Add space volume strategy detection

Detect whether a space can be built as a clipped extrusion or needs
a B-rep fallback, based on wall face orientation and top/bottom
bounding planes.

Generated with the assistance of an AI coding tool.

src/ifcopenshell-python/ifcopenshell/util/space.py

@@ -345,3 +345,60 @@ def get_vertical_bounding_planes(
         planes.append((anchor, mean_normal))
 
     return "EXTRUDE_CLIP", planes
+
+
+def detect_space_volume_strategy(
+    ifc_file: ifcopenshell.file,
+    shapes: dict,
+    tree: ifcopenshell.geom.tree,
+    space_polygon: shapely.Polygon,
+    base_z: float,
+    bounding_walls: list[ifcopenshell.entity_instance],
+    start_z: Optional[float] = None,
+) -> tuple[str, Optional[list], Optional[list]]:
+    """Decide whether a space can be represented as a clipped extrusion.
+
+    A space is "EXTRUDE_CLIP" when all bounding walls have vertical side faces
+    and the detected top/bottom bounding planes are few and piecewise-planar
+    (0-2 top planes, 0-1 bottom plane). Otherwise it is "BREP".
+
+    :param ifc_file: The IFC file.
+    :param shapes: Cached element shapes.
+    :param tree: Geometry tree with bounding elements.
+    :param space_polygon: Space footprint in world XY.
+    :param base_z: Base elevation in SI.
+    :param bounding_walls: List of wall elements bounding the space.
+    :param start_z: Ray-cast origin elevation (RL cut level) in SI.
+    :return: ("EXTRUDE_CLIP", top_planes, bottom_planes) or ("BREP", None, None).
+    """
+    tol = 0.02
+    for wall in bounding_walls:
+        shape_data = shapes.get(wall.id())
+        if not shape_data:
+            continue
+        verts = shape_data["verts"]
+        faces = shape_data["faces"]
+        if len(verts) == 0 or len(faces) == 0:
+            continue
+        v1 = verts[faces[:, 1]] - verts[faces[:, 0]]
+        v2 = verts[faces[:, 2]] - verts[faces[:, 0]]
+        normals = np.cross(v1, v2)
+        norms = np.linalg.norm(normals, axis=1)
+        normals = normals[norms > 1e-8]
+        if len(normals) == 0:
+            continue
+        normals = normals / np.linalg.norm(normals, axis=1)[:, np.newaxis]
+        side_mask = np.abs(normals[:, 2]) < 0.5
+        if np.any(side_mask) and np.mean(np.abs(normals[side_mask, 2])) > tol:
+            return "BREP", None, None
+
+    _, top_planes = get_vertical_bounding_planes(ifc_file, shapes, tree, space_polygon, base_z, "UP", start_z=start_z)
+
+    _, bottom_planes = get_vertical_bounding_planes(
+        ifc_file, shapes, tree, space_polygon, base_z, "DOWN", start_z=start_z
+    )
+
+    if len(top_planes) > 2 or len(bottom_planes) > 1:
+        return "BREP", None, None
+
+    return "EXTRUDE_CLIP", top_planes, bottom_planes

src/ifcopenshell-python/test/util/test_space.py

@@ -48,7 +48,7 @@ def _build_shapes_dict(ifc_file, elements):
     return shapes
 
 
-def _add_extruded_body(ifc_file, element, coords_2d, depth, z_offset=0.0):
+def _add_extruded_body(ifc_file, element, coords_2d, depth, z_offset=0.0, direction=(0.0, 0.0, 1.0)):
     """Add a body representation (extruded polyline) to an element."""
     if not ifc_file.by_type("IfcProject"):
         ifcopenshell.api.root.create_entity(ifc_file, ifc_class="IfcProject")
@@ -76,7 +76,7 @@ def _add_extruded_body(ifc_file, element, coords_2d, depth, z_offset=0.0):
         ifc_file.createIfcDirection((0.0, 0.0, 1.0)),
         ifc_file.createIfcDirection((1.0, 0.0, 0.0)),
     )
-    direction = ifc_file.createIfcDirection((0.0, 0.0, 1.0))
+    direction = ifc_file.createIfcDirection(direction)
     solid = ifc_file.createIfcExtrudedAreaSolid(profile, placement, direction, depth)
     rep = ifc_file.create_entity(
         "IfcShapeRepresentation",
@@ -221,3 +221,47 @@ class TestGetVerticalBoundingPlanes(test.bootstrap.IFC4):
         assert strategy == "EXTRUDE_CLIP"
         assert len(planes) == 1
         assert np.allclose(planes[0][0], [0.0, 0.0, 3.0], atol=0.1)
+
+
+class TestDetectSpaceVolumeStrategy(test.bootstrap.IFC4):
+    def test_vertical_walls_flat_slab_returns_extrude_clip(self):
+        wall = ifcopenshell.api.root.create_entity(self.file, ifc_class="IfcWall")
+        slab = ifcopenshell.api.root.create_entity(self.file, ifc_class="IfcSlab")
+        _add_extruded_body(self.file, wall, [[-5, -5], [5, -5], [5, 5], [-5, 5]], 3.0)
+        _add_extruded_body(self.file, slab, [[-5, -5], [5, -5], [5, 5], [-5, 5]], 0.3, z_offset=3.0)
+        shapes = _build_shapes_dict(self.file, [wall, slab])
+        tree = ifcopenshell.geom.tree(self.file)
+        tree.add_file(self.file, ifcopenshell.geom.settings())
+        strategy, top, bottom = subject.detect_space_volume_strategy(
+            self.file, shapes, tree, shapely.box(-5, -5, 5, 5), 0.0, [wall]
+        )
+        assert strategy == "EXTRUDE_CLIP"
+        assert len(top) == 1
+        assert len(bottom) == 0
+
+    def test_vertical_walls_flat_slab_returns_extrude_clip_from_rl_origin(self):
+        # Same as above but rays cast from an RL cut elevation (z=1.0).
+        wall = ifcopenshell.api.root.create_entity(self.file, ifc_class="IfcWall")
+        slab = ifcopenshell.api.root.create_entity(self.file, ifc_class="IfcSlab")
+        _add_extruded_body(self.file, wall, [[-5, -5], [5, -5], [5, 5], [-5, 5]], 3.0)
+        _add_extruded_body(self.file, slab, [[-5, -5], [5, -5], [5, 5], [-5, 5]], 0.3, z_offset=3.0)
+        shapes = _build_shapes_dict(self.file, [wall, slab])
+        tree = ifcopenshell.geom.tree(self.file)
+        tree.add_file(self.file, ifcopenshell.geom.settings())
+        strategy, top, bottom = subject.detect_space_volume_strategy(
+            self.file, shapes, tree, shapely.box(-5, -5, 5, 5), 0.0, [wall], start_z=1.0
+        )
+        assert strategy == "EXTRUDE_CLIP"
+        assert len(top) == 1
+        assert len(bottom) == 0
+
+    def test_sloped_wall_returns_brep(self):
+        wall = ifcopenshell.api.root.create_entity(self.file, ifc_class="IfcWall")
+        _add_extruded_body(self.file, wall, [[-5, -5], [5, -5], [5, 5], [-5, 5]], 6.0, direction=(0.0, 0.5, 1.0))
+        shapes = _build_shapes_dict(self.file, [wall])
+        tree = ifcopenshell.geom.tree(self.file)
+        tree.add_file(self.file, ifcopenshell.geom.settings())
+        strategy, _, _ = subject.detect_space_volume_strategy(
+            self.file, shapes, tree, shapely.box(-4, -4, 4, 4), 0.0, [wall]
+        )
+        assert strategy == "BREP"