ifc5d: measure openings in their real orientation on both take-off engines

See #6835. Qto_OpeningElementBaseQuantities came out axis-scrambled for
openings authored in a Z-up local frame (X along the voided wall, Y
through it, Z vertical), which is how Bonsai authors every wall opening:

- The IfcOpenShell engine mapped Height to the local Y extent and Depth
  to the local Z extent, so a 0.9 x 2.0 door opening with Bonsai's
  default 1.2m void depth reported Height 1.2 and Depth 2.0, and Area
  (max side area) picked the through-wall side, 2.4 instead of 1.8.
  This matches the wrong Height=1.2/Area=1.2 screenshots reported for a
  1x1 window opening in #6835.
- The Blender engine mapped opening Width to get_length, which returns
  the longest bounding box edge, i.e. the opening height for typical
  door openings (the same defect 4adaf0d fixed for IfcDoor Width), and
  get_opening_depth used min(x, y), which returns the opening width
  whenever the width is smaller than the void depth.

The IfcOpenShell engine now has opening-aware internal calculators
(get_opening_width/height/depth/area) that detect horizontal (slab
style) openings with the same heuristic as the Blender calculator, so
slab opening depths keep reporting the slab thickness. The Blender
ruleset uses get_x for opening Width, and get_opening_depth measures the
through-element Y extent for vertical openings.

Door and window quantities themselves are addressed separately: the
Blender engine door Width was fixed in 4adaf0d, and the remaining
door/window defects (door not quantified on the IfcOpenShell engine,
inflated areas) are fixed by the attribute-based calculators in #8389.

Generated with the assistance of an AI coding tool.

src/bonsai/bonsai/bim/module/qto/calculator.py

@@ -225,7 +225,7 @@ def get_opening_depth(obj: bpy.types.Object) -> float:
     if is_opening_horizontal(obj):
         return get_height(obj)
     else:
-        return get_width(obj)
+        return get_y(obj)
 
 
 def get_opening_mapping_area(obj: bpy.types.Object) -> float:

src/ifc5d/ifc5d/IFC4QtoBaseQuantities.json

@@ -383,11 +383,11 @@
             },
             "IfcOpeningElement": {
                 "Qto_OpeningElementBaseQuantities": {
-                    "Area": "gross_get_max_side_area",
+                    "Area": "gross_get_opening_area",
-                    "Depth": "gross_get_z",
+                    "Depth": "gross_get_opening_depth",
-                    "Height": "gross_get_y",
+                    "Height": "gross_get_opening_height",
                     "Volume": "gross_get_volume",
-                    "Width": "gross_get_x"
+                    "Width": "gross_get_opening_width"
                 }
             },
             "IfcOutlet": {

src/ifc5d/ifc5d/IFC4QtoBaseQuantitiesBlender.json

@@ -387,7 +387,7 @@
                     "Depth": "get_opening_depth",
                     "Height": "get_opening_height",
                     "Volume": "get_net_volume",
-                    "Width": "get_length"
+                    "Width": "get_x"
                 }
             },
             "IfcOutlet": {

src/ifc5d/ifc5d/IFC4X3QtoBaseQuantities.json

@@ -472,11 +472,11 @@
             },
             "IfcOpeningElement": {
                 "Qto_OpeningElementBaseQuantities": {
-                    "Area": "gross_get_max_side_area",
+                    "Area": "gross_get_opening_area",
-                    "Depth": "gross_get_z",
+                    "Depth": "gross_get_opening_depth",
-                    "Height": "gross_get_y",
+                    "Height": "gross_get_opening_height",
                     "Volume": "gross_get_volume",
-                    "Width": "gross_get_x"
+                    "Width": "gross_get_opening_width"
                 }
             },
             "IfcOutlet + IfcOutletType": {

src/ifc5d/ifc5d/IFC4X3QtoBaseQuantitiesBlender.json

@@ -476,7 +476,7 @@
                     "Depth": "get_opening_depth",
                     "Height": "get_opening_height",
                     "Volume": "get_net_volume",
-                    "Width": "get_length"
+                    "Width": "get_x"
                 }
             },
             "IfcOutlet + IfcOutletType": {

src/ifc5d/ifc5d/qto.py

@@ -254,6 +254,17 @@ class IfcOpenShell(QtoCalculator):
         "get_segment_length": Function(
             "IfcLengthMeasure", "Segment Length", "Intelligently guesses the length of flow segments"
         ),
+        "get_opening_width": Function(
+            "IfcLengthMeasure", "Opening Width", "The width of an opening, guessing the opening orientation"
+        ),
+        "get_opening_height": Function(
+            "IfcLengthMeasure", "Opening Height", "The height of an opening, guessing the opening orientation"
+        ),
+        "get_opening_depth": Function(
+            "IfcLengthMeasure",
+            "Opening Depth",
+            "The depth of an opening (through the voided element), guessing the opening orientation",
+        ),
         # IfcAreaMeasure
         "get_area": Function("IfcAreaMeasure", "Area", "The total surface area of the element"),
         "get_footprint_area": Function(
@@ -276,6 +287,9 @@ class IfcOpenShell(QtoCalculator):
             "Side area",
             "The side (non-projected) are of the shape as seen from the local Y-axis",
         ),
+        "get_opening_area": Function(
+            "IfcAreaMeasure", "Opening Area", "The area of an opening, guessing the opening orientation"
+        ),
         "get_top_area": Function(
             "IfcAreaMeasure",
             "Top area",
@@ -301,6 +315,10 @@ class IfcOpenShell(QtoCalculator):
     internal_functions = (
         "get_segment_length",
         "get_weight",
+        "get_opening_width",
+        "get_opening_height",
+        "get_opening_depth",
+        "get_opening_area",
     )
 
     @classmethod
@@ -365,6 +383,9 @@ class IfcOpenShell(QtoCalculator):
                                 value = cls.get_weight(element, geometry, calculation_type)
                                 if value is None:
                                     continue
+                            elif formula.startswith("get_opening_"):
+                                value = cls.get_opening_quantity(geometry, formula)
+                                value = cls.unit_converter.convert(value, IfcOpenShell.raw_functions[formula].measure)
                             else:
                                 value = formula_functions[formula](geometry)
                                 assert isinstance(value, (float, int))
@@ -389,6 +410,34 @@ class IfcOpenShell(QtoCalculator):
             )
         return iterators
 
+    @classmethod
+    def get_opening_quantity(cls, geometry: ifcopenshell.geom.ShapeType, formula: str) -> float:
+        """Get an opening dimension or area, guessing the opening orientation.
+
+        Vertical (wall) openings are measured in a Z-up local frame: X along
+        the voided element, Y through it, Z vertical. An opening is treated as
+        horizontal (e.g. voiding a slab) when its Z extent is smaller than
+        both X and Y, matching the Blender calculator's heuristic.
+
+        :param geometry: Geometry output calculated by IfcOpenShell
+        :param formula: One of the ``get_opening_*`` internal function names.
+        :return: The dimension or area in SI units.
+        """
+        x = ifcopenshell.util.shape.get_x(geometry)
+        y = ifcopenshell.util.shape.get_y(geometry)
+        z = ifcopenshell.util.shape.get_z(geometry)
+        is_horizontal = z < x and z < y
+        if formula == "get_opening_width":
+            return x
+        if formula == "get_opening_height":
+            return min(x, y) if is_horizontal else z
+        if formula == "get_opening_depth":
+            return z if is_horizontal else y
+        assert formula == "get_opening_area"
+        if is_horizontal:
+            return ifcopenshell.util.shape.get_footprint_area(geometry)
+        return ifcopenshell.util.shape.get_side_area(geometry)
+
     @classmethod
     def get_segment_length(cls, element: ifcopenshell.entity_instance) -> Union[float, None]:
         """Get segment length.

src/ifc5d/test/test_qto.py

@@ -0,0 +1,92 @@
+# Ifc5D - IFC costing utility
+# Copyright (C) 2026 Dion Moult <dion@thinkmoult.com>
+#
+# This file is part of Ifc5D.
+#
+# Ifc5D is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Lesser General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# Ifc5D is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public License
+# along with Ifc5D.  If not, see <http://www.gnu.org/licenses/>.
+
+# This file was generated with the assistance of an AI coding tool.
+
+import ifcopenshell
+import ifcopenshell.api.context
+import ifcopenshell.api.root
+import ifcopenshell.api.unit
+import pytest
+
+import ifc5d.qto
+
+
+class TestOpeningQuantities:
+    """Openings authored in a Z-up local frame, as produced by Bonsai (#6835)."""
+
+    def setup_method(self):
+        self.file = ifcopenshell.file(schema="IFC4X3")
+        ifcopenshell.api.root.create_entity(self.file, ifc_class="IfcProject", name="Test")
+        f = self.file
+        units = [
+            f.createIfcSIUnit(None, "LENGTHUNIT", None, "METRE"),
+            f.createIfcSIUnit(None, "AREAUNIT", None, "SQUARE_METRE"),
+            f.createIfcSIUnit(None, "VOLUMEUNIT", None, "CUBIC_METRE"),
+        ]
+        ifcopenshell.api.unit.assign_unit(self.file, units=units)
+        model = ifcopenshell.api.context.add_context(self.file, context_type="Model")
+        self.body = ifcopenshell.api.context.add_context(
+            self.file, context_type="Model", context_identifier="Body", target_view="MODEL_VIEW", parent=model
+        )
+
+    def create_opening(self, profile_x: float, profile_y: float, position, extrude_dir, depth: float):
+        f = self.file
+        opening = ifcopenshell.api.root.create_entity(f, ifc_class="IfcOpeningElement")
+        opening.ObjectPlacement = f.createIfcLocalPlacement(
+            None, f.createIfcAxis2Placement3D(f.createIfcCartesianPoint((0.0, 0.0, 0.0)), None, None)
+        )
+        profile = f.createIfcRectangleProfileDef("AREA", None, None, profile_x, profile_y)
+        solid = f.createIfcExtrudedAreaSolid(profile, position, f.createIfcDirection(extrude_dir), depth)
+        rep = f.createIfcShapeRepresentation(self.body, "Body", "SweptSolid", [solid])
+        opening.Representation = f.createIfcProductDefinitionShape(None, None, [rep])
+        return opening
+
+    def quantify(self, opening) -> dict[str, float]:
+        rules = ifc5d.qto.rules["IFC4X3QtoBaseQuantities"]
+        results = ifc5d.qto.quantify(self.file, {opening}, rules)
+        return results[opening]["Qto_OpeningElementBaseQuantities"]
+
+    def test_vertical_wall_opening(self):
+        # A 0.9 x 2.0 door opening voiding a wall along +Y, with Bonsai's
+        # oversized 1.2m void depth: local extents x=0.9, y=1.2, z=2.0.
+        f = self.file
+        position = f.createIfcAxis2Placement3D(
+            f.createIfcCartesianPoint((0.0, -0.6, 1.0)),
+            f.createIfcDirection((0.0, -1.0, 0.0)),
+            f.createIfcDirection((1.0, 0.0, 0.0)),
+        )
+        opening = self.create_opening(0.9, 2.0, position, (0.0, 0.0, -1.0), 1.2)
+        quantities = self.quantify(opening)
+        assert quantities["Width"] == pytest.approx(0.9)
+        assert quantities["Height"] == pytest.approx(2.0)
+        assert quantities["Depth"] == pytest.approx(1.2)
+        assert quantities["Area"] == pytest.approx(1.8)
+        assert quantities["Volume"] == pytest.approx(2.16)
+
+    def test_horizontal_slab_opening(self):
+        # A 1.0 x 0.5 opening voiding a 0.3 thick slab: extents x=1.0, y=0.5, z=0.3.
+        f = self.file
+        position = f.createIfcAxis2Placement3D(f.createIfcCartesianPoint((0.0, 0.0, 0.0)), None, None)
+        opening = self.create_opening(1.0, 0.5, position, (0.0, 0.0, -1.0), 0.3)
+        quantities = self.quantify(opening)
+        assert quantities["Width"] == pytest.approx(1.0)
+        assert quantities["Height"] == pytest.approx(0.5)
+        assert quantities["Depth"] == pytest.approx(0.3)
+        assert quantities["Area"] == pytest.approx(0.5)
+        assert quantities["Volume"] == pytest.approx(0.15)