get_top_area to calculate area for the roof #5899

src/ifc5d/ifc5d/IFC4QtoBaseQuantities.json

@@ -484,8 +484,8 @@
             },
             "IfcRoof": {
                 "Qto_RoofBaseQuantities": {
-                    "GrossArea": null,
-                    "NetArea": null,
+                    "GrossArea": "gross_get_top_area",
+                    "NetArea": "net_get_top_area",
                     "ProjectedArea": null
                 }
             },

src/ifc5d/ifc5d/qto.py

@@ -145,6 +145,11 @@ class IfcOpenShell:
             "Side area",
             "The side (non-projected) are of the shape as seen from the local Y-axis",
         ),
+        "get_top_area": Function(
+            "IfcAreaMeasure",
+            "Top area",
+            "The total surface area deviating by no more than 45 degrees from the local Z+ axis.",
+        ),
         # IfcVolumeMeasure
         "get_volume": Function("IfcVolumeMeasure", "Volume", "Calculates the volume of a manifold shape"),
     }

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

@@ -532,6 +532,10 @@ def get_max_side_area(geometry: ShapeType) -> float:
     return max(get_side_area(geometry, axis="X"), get_side_area(geometry, axis="Y"), get_side_area(geometry, axis="Z"))
 
 
+def get_top_area(geometry: ShapeType) -> float:
+    return get_side_area(geometry, axis="Z", angle=45)
+
+
 def get_footprint_area(
     geometry: ShapeType,
     axis: AXIS_LITERAL = "Z",