New formwork area calculation feature

src/blenderbim/blenderbim/bim/module/qto/helper.py

@@ -1,3 +1,4 @@
+import bpy
 import bmesh
 
 
@@ -11,3 +12,50 @@ def calculate_volume(obj):
     result = bm.calc_volume()
     bm.free()
     return result
+
+
+def calculate_formwork_area(objs):
+    """
+    Formwork is defined as the surface area required to cover all exposed
+    surfaces of one or more objects, excluding top surfaces (i.e. that have a
+    face normal with a significant Z component).
+    """
+    copied_objs = []
+    result = 0
+
+    for obj in objs:
+        new_obj = obj.copy()
+        new_obj.data = obj.data.copy()
+        new_obj.animation_data_clear()
+        bpy.context.collection.objects.link(new_obj)
+        copied_objs.append(new_obj)
+
+    context_override = {}
+    context_override["object"] = context_override["active_object"] = copied_objs[0]
+    context_override["selected_objects"] = context_override["selected_editable_objects"] = copied_objs
+    bpy.ops.object.join(context_override)
+
+    copied_objs[0].name = "Formwork"
+    copied_objs[0].BIMObjectProperties.ifc_definition_id = 0
+    modifier = copied_objs[0].modifiers.new("Formwork", "REMESH")
+    modifier.mode = "SHARP"
+    # This hardcoded value may be optimised through a better understanding of the octree division.
+    # These values are based off some trial and error heuristics I've learned through experience.
+    max_dim = max(copied_objs[0].dimensions)
+    if max_dim > 45:
+        modifier.octree_depth = 9
+    elif max_dim > 35:
+        modifier.octree_depth = 8
+    elif max_dim > 12:
+        modifier.octree_depth = 7
+    elif max_dim > 5:
+        modifier.octree_depth = 6
+    else:
+        modifier.octree_depth = 5
+
+    mesh = copied_objs[0].evaluated_get(bpy.context.evaluated_depsgraph_get()).to_mesh()
+    for polygon in mesh.polygons:
+        if polygon.normal.z > 0.5:
+            continue
+        result += polygon.area
+    return result

src/blenderbim/blenderbim/bim/module/qto/operator.py

@@ -69,6 +69,8 @@ class ExecuteQtoMethod(bpy.types.Operator):
         elif props.qto_methods == "VOLUME":
             for obj in bpy.context.selected_objects:
                 result += helper.calculate_volume(obj)
+        elif props.qto_methods == "FORMWORK":
+            result = helper.calculate_formwork_area(bpy.context.selected_objects)
         props.qto_result = str(round(result, 3))
         return {"FINISHED"}
 
@@ -88,6 +90,8 @@ class QuantifyObjects(bpy.types.Operator):
                 result = helper.calculate_height(obj)
             elif props.qto_methods == "VOLUME":
                 result = helper.calculate_volume(obj)
+            elif props.qto_methods == "FORMWORK":
+                result = helper.calculate_formwork_area([obj])
             if not result:
                 continue
             result = round(result, 3)