Fix #6182. For convenience, precalculate scale value for projected CRS map unit map conversion

src/bonsai/bonsai/bim/prop.py

@@ -235,6 +235,11 @@ def update_is_null(self: "Attribute", context: bpy.types.Context) -> None:
             self.set_value(default)
         if self.is_null is not True:
             self.is_null = True
+    if self.update:
+        update = globals()
+        for name in self.update.split("."):
+            update = update[name] if isinstance(update, dict) else getattr(update, name)
+        update(self, context)
 
 
 def set_int_value(self: "Attribute", new_value: int) -> None:
@@ -322,6 +327,7 @@ class Attribute(PropertyGroup):
     value_max_constraint: BoolProperty(default=False, description="True if the numerical value has an upper bound")
     special_type: StringProperty(name="Special Value Type", default="")
     metadata: StringProperty(name="Metadata", description="For storing some additional information about the attribute")
+    update: StringProperty(name="Update", description="Custom update function to be executed")
 
     if TYPE_CHECKING:
         name: str

src/bonsai/bonsai/tool/georeference.py

@@ -58,6 +58,7 @@ class Georeference(bonsai.core.tool.Georeference):
                 )
                 if data["MapUnit"]:
                     new.enum_value = str(data["MapUnit"].id())
+                new.update = "tool.Georeference.update_map_unit"
                 return True
 
         props = bpy.context.scene.BIMGeoreferenceProperties
@@ -72,6 +73,21 @@ class Georeference(bonsai.core.tool.Georeference):
                 bonsai.bim.helper.import_attributes2(projected_crs, props.projected_crs, callback=callback)
                 return
 
+    @classmethod
+    def update_map_unit(cls, self, context) -> None:
+        if unit_id := self.get_value():
+            map_unit = tool.Ifc.get().by_id(int(unit_id))
+            project_unit = ifcopenshell.util.unit.get_project_unit(tool.Ifc.get(), "LENGTHUNIT")
+            if map_unit and project_unit:
+                result = ifcopenshell.util.unit.convert_unit(1, project_unit, map_unit)
+            else:
+                result = 1.0
+        else:
+            result = 1.0
+        for attribute in bpy.context.scene.BIMGeoreferenceProperties.coordinate_operation:
+            if attribute.name == "Scale":
+                attribute.set_value(str(result))
+
     @classmethod
     def import_coordinate_operation(cls) -> None:
         def callback(name, prop, data):