Create IFC Diff tool, showing added, removed, and modified.

It produces a JSON output of exactly what changed. It requires a patched version of the DeepDiff library, which I will provide.

src/ifcdiff/diff.py

@@ -0,0 +1,109 @@
+import ifcopenshell
+from deepdiff import DeepDiff
+import time
+import json
+
+class IfcDiff():
+    def __init__(self, old_file, new_file):
+        self.old_file = old_file
+        self.new_file = new_file
+        self.change_register = {}
+        self.representation_ids = []
+
+    def diff(self):
+        print('# IFC Diff')
+        self.load()
+
+        old_elements = set(e.GlobalId for e in self.old.by_type('IfcElement'))
+        new_elements = set(e.GlobalId for e in self.new.by_type('IfcElement'))
+
+        self.deleted_elements = old_elements - new_elements
+        self.added_elements = new_elements - old_elements
+        same_elements = new_elements - self.added_elements
+        total_same_elements = len(same_elements)
+
+        print(' - {} item(s) were deleted'.format(len(self.deleted_elements)))
+        print(' - {} item(s) were added'.format(len(self.added_elements)))
+        print(' - {} item(s) were retained between the old and new IFC file'.format(total_same_elements))
+
+        start = time.time()
+        total_diffed = 0
+
+        for global_id in same_elements:
+            total_diffed += 1
+            print('{}/{} diffed ...'.format(total_diffed, total_same_elements), end='\r', flush=True)
+            old_element = self.old.by_id(global_id)
+            new_element = self.new.by_id(global_id)
+            self.diff_element(old_element, new_element)
+
+            representation_id = self.get_representation_id(new_element)
+            if representation_id in self.representation_ids:
+                continue
+            self.representation_ids.append(representation_id)
+            self.diff_element_geometry(old_element, new_element)
+
+        print(' - {} item(s) were changed either geometrically or with data'.format(
+            len(self.change_register.keys())))
+        print('# Diff finished in {:.2f} seconds'.format(time.time() - start))
+
+    def load(self):
+        print('Loading old file ...')
+        self.old = ifcopenshell.open(self.old_file)
+        print('Loading new file ...')
+        self.new = ifcopenshell.open(self.new_file)
+
+    def diff_element(self, old_element, new_element):
+        diff = DeepDiff(old_element, new_element,
+            significant_digits=2, ignore_string_type_changes=True, ignore_numeric_type_changes=True,
+            exclude_regex_paths=[
+                r'root.*id$',
+                r'.*Representation.*',
+                r'.*OwnerHistory.*',
+                r'.*ObjectPlacement.*',
+                ])
+        if diff and new_element.GlobalId:
+            self.change_register.setdefault(new_element.GlobalId, {}).update(diff)
+
+    def diff_element_geometry(self, old_element, new_element):
+        try:
+            DeepDiff(old_element.ObjectPlacement, new_element.ObjectPlacement,
+                terminate_on_first=True,
+                significant_digits=2, ignore_string_type_changes=True, ignore_numeric_type_changes=True,
+                exclude_regex_paths=r'root.*id$')
+            DeepDiff(old_element.Representation, new_element.Representation,
+                terminate_on_first=True,
+                skip_after_n=1000, # Arbitrary value to "skim" check
+                significant_digits=2, ignore_string_type_changes=True, ignore_numeric_type_changes=True,
+                exclude_regex_paths=r'root.*id$')
+        except:
+            if new_element.GlobalId:
+                return self.change_register.setdefault(new_element.GlobalId, {}).update({'has_geometry_change': True})
+
+    def get_representation_id(self, element):
+        if not element.Representation:
+            return None
+        for representation in element.Representation.Representations:
+            if not representation.is_a('IfcShapeRepresentation'):
+                continue
+            if representation.RepresentationIdentifier == 'Body' \
+                and representation.RepresentationType != 'MappedRepresentation':
+                return representation.id()
+            elif representation.RepresentationIdentifier == 'Body':
+                return representation.Items[0].MappingSource.MappedRepresentation.id()
+
+ifc_diff = IfcDiff('old.ifc', 'new.ifc')
+ifc_diff.diff()
+
+class DiffEncoder(json.JSONEncoder):
+    def default(self, obj):
+        try:
+            return json.JSONEncoder.default(self, obj)
+        except:
+            return str(obj)
+
+with open('diff.json', 'w', encoding='utf-8') as diff_file:
+    json.dump({
+        'added': list(ifc_diff.added_elements),
+        'deleted': list(ifc_diff.deleted_elements),
+        'changed': ifc_diff.change_register,
+        }, diff_file, indent=4, cls=DiffEncoder)