How to update a Blender scene when the FBX or OBJ model is revised

Why a revised model breaks your Blender scene

Visualization work usually starts with a model from someone else: an architect, a CAD or BIM team, a product designer. You import the FBX or OBJ and spend days on materials, modifiers and layout. Then a revised export arrives.

Importing the new file again gives you fresh objects with the importer's default materials, while the work you did sits on the old ones. Deleting the old scene throws that work away. Keeping both leaves you comparing two piles of objects by eye.

What decides whether a revision can be reconciled

The question is how the new file says which object is which.

• A stable ID per object. If the exporter writes the same unique ID on an object in every revision, as a text or integer property, objects can be matched even when they are moved or renamed. Not every CAD or BIM exporter writes one.
• Unique names. Without IDs, an exact and unique name is the fallback. It is weaker: a renamed object looks like one removed and one added.
• Unique material names. The source material names are how your material choices find the right slots on the updated object.

A manual workflow

1. Import the original model into its own collection and keep the unmodified source file.
2. When the revision arrives, import it into a separate collection instead of over the old objects.
3. Match objects by ID, or by exact name where there is no ID, and sort them into added, changed, unchanged and removed.
4. For each changed object, move your materials and modifiers onto the new geometry, matching material slots by the source material names.
5. Decide per object whether the source position or your local position wins, and check the parent relationships you added.
6. Save a versioned copy of the .blend before you replace anything, so you can go back.

Doing the same review with Karelia Revision

Karelia Revision is a Blender add-on that does this comparison for FBX and OBJ revisions, and asks before it changes anything.

• It imports your original model into an owned baseline collection. You finish the scene there.
• You stage the revised source file and review added, changed, unchanged, removed and blocked objects, with counts and reasons.
• Updated objects keep their local modifier stacks and material choices when the source material names are unique and the local slot count is unchanged.
• You apply only what you select, and you can export a JSON report of the preview first.
• The latest apply can be reversed from the Recovery section after you save and reopen the file.

Check your exporter first

Whether an ID survives depends on the exporter. If the field you configured is missing, Karelia Revision lists the text and integer property fields that were actually exported, so you can see what your exporter wrote. It does not silently pick another field.

Revit and Archicad exports do not all carry usable stable IDs, and the add-on does not assume they do. Karelia Revision is a beta, tested on Windows with Blender 4.5.14 LTS and synthetic FBX and OBJ revisions. Try it on a copy of your own files first.