Dissolve specifically IOS triangulated edges for meshes instead of generic Blender limited dissolve.

src/blenderbim/blenderbim/bim/import_ifc.py

@@ -1823,6 +1823,10 @@ class IfcImporter:
                 loop_total = [3] * num_loops
                 num_vertex_indices = len(geometry.faces)
 
+                # See bug 3546
+                # ios_edges holds true edges that aren't triangulated.
+                mesh["ios_edges"] = list(set(tuple(e) for e in grouped_edges))
+
                 mesh.vertices.add(num_vertices)
                 mesh.vertices.foreach_set("co", verts)
                 mesh.loops.add(num_vertex_indices)
@@ -1909,7 +1913,7 @@ class IfcImportSettings:
         self.should_merge_materials_by_colour = False
         self.should_load_geometry = True
         self.should_use_native_meshes = False
-        self.should_clean_mesh = True
+        self.should_clean_mesh = False
         self.should_cache = True
         self.is_coordinating = True
         self.deflection_tolerance = 0.001

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

@@ -1360,6 +1360,7 @@ class OverrideModeSetEdit(bpy.types.Operator):
                         should_sync_changes_first=False,
                         apply_openings=False,
                     )
+                tool.Geometry.dissolve_triangulated_edges(obj)
                 obj.data.BIMMeshProperties.mesh_checksum = tool.Geometry.get_mesh_checksum(obj.data)
             else:
                 obj.select_set(False)

src/blenderbim/blenderbim/bim/module/project/prop.py

@@ -151,7 +151,7 @@ class BIMProjectProperties(PropertyGroup):
     should_stream: BoolProperty(name="Stream Data From IFC-SPF (Only for advanced users)", default=False)
     should_load_geometry: BoolProperty(name="Load Geometry", default=True)
     should_use_native_meshes: BoolProperty(name="Native Meshes", default=False)
-    should_clean_mesh: BoolProperty(name="Clean Meshes", default=True)
+    should_clean_mesh: BoolProperty(name="Clean Meshes", default=False)
     should_cache: BoolProperty(name="Cache", default=False)
     is_coordinating: BoolProperty(name="For Coordination Only", default=False)
     deflection_tolerance: FloatProperty(name="Deflection Tolerance", default=0.001)

src/blenderbim/blenderbim/bim/ui.py

@@ -247,7 +247,7 @@ class BIM_ADDON_preferences(bpy.types.AddonPreferences):
         row.operator("bim.select_data_dir", icon="FILE_FOLDER", text="")
 
         row = self.layout.row(align=True)
-        row.prop(context.scene.BIMProperties, "psets_dir")
+        row.prop(context.scene.BIMProperties, "pset_dir")
         row = self.layout.row(align=True)
         row.prop(context.scene.DocProperties, "sheets_dir")
         row = self.layout.row(align=True)

src/blenderbim/blenderbim/tool/geometry.py

@@ -118,6 +118,21 @@ class Geometry(blenderbim.core.tool.Geometry):
         except:
             pass
 
+    @classmethod
+    def dissolve_triangulated_edges(cls, obj):
+        if obj.data and "ios_edges" in obj.data:
+            bm = bmesh.new()
+            bm.from_mesh(obj.data)
+            edges_to_keep = set(map(frozenset, obj.data["ios_edges"]))
+            edges_to_dissolve = []
+            for edge in bm.edges:
+                if frozenset([vert.index for vert in edge.verts]) not in edges_to_keep:
+                    edges_to_dissolve.append(edge)
+            bmesh.ops.dissolve_edges(bm, edges=edges_to_dissolve)
+            bm.to_mesh(obj.data)
+            bm.free()
+            del obj.data["ios_edges"]
+
     @classmethod
     def does_representation_id_exist(cls, representation_id):
         try: