BIMScript

Material-Aware Structured Scene Programs for BIM Ingestion

Prakash Kondibhau Naikade · Thomas B. Moeslund · Andreas Møgelmose

_{AI:Xpertise Lab · Visual Analysis and Perception Laboratory · CREATE, Aalborg University · Pioneer Centre for Artificial Intelligence, Denmark}

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📌 Contents

• Overview
• Highlights
• The output is a program
• Results
• Revit & IFC ingestion
• Code release
• Project page
• Citation
• License

🔎 Overview

BIMScript reconstructs an indoor scene as a short program of parametric commands. Each element carries not only geometry but the material and condition that a building model needs, and each command maps one-to-one onto a native Revit / IFC object. The paper answers three questions that stand between structured-language scene models (such as SceneScript) and automated BIM ingestion:

Question	Answer in BIMScript
What is the scene made of?	Per-element material= and condition= tokens, supervised by a VLM-distilled material passport over 1.9M elements in ~100k scenes
How fast can it be produced?	GraphStep, an output-exact CUDA-graph decoder (3.4× per step), plus SchemaDraft, grammar-parallel draft-and-verify
Exactly where is each element?	SubBin, a bounded sub-bin offset head that lifts coordinates off the 5 cm token grid

✨ Highlights

• 🧱 Material + condition per element. 14 materials and 5 conditions, predicted alongside geometry with no loss in layout accuracy.
• ⚡ 3.4× faster decoding. Decoding is bound by launch and sync overhead, not compute. GraphStep cuts 6.40 → 1.91 ms/step without retraining.
• 🎯 Sub-grid precision. SubBin roughly doubles F1@2 cm (0.034 → 0.071).
• 🏗️ Straight into BIM. A pyRevit add-in creates native walls, hosted doors and windows, and exports to IFC4.
• 🤖 LLM-ready. The output is plain language, so LLMs can reason over it for embodied carbon, LCA, circularity and reuse.

🧾 The output is a program

Real decoder output. Each line is an object with parameters, so it is readable, diffable, editable, and maps one-to-one onto a BIM element.

make_wall,   id=0, a_x=-5.922, a_y=8.741, a_z=-0.002, b_x=-1.907, b_y=8.757, b_z=-0.002,
             height=2.700, thickness=0.0, material=wood_paneling, condition=good
make_wall,   id=1, a_x=-1.907, a_y=8.757, a_z=-0.002, b_x=-1.875, b_y=1.616, b_z=-0.002,
             height=2.700, thickness=0.0, material=wallpaper,     condition=good
make_door,   id=1000, wall0_id=1, position_x=-1.891, position_y=5.186, position_z=1.012,
             width=0.920, height=2.024, material=composite,       condition=new
make_window, id=2000, wall0_id=0, position_x=-3.914, position_y=8.749, position_z=1.520,
             width=1.480, height=1.200, material=aluminum,        condition=good

📊 Results

1,000-scene held-out test split with one greedy decode per scene. Attributes are scored on elements matched within 10 cm. Latency is batch 1 with GraphStep on one L40S.

Model	F1@5cm	Avg F1	Coverage	Mat. acc.	Cond. acc.	Params	s / scene
SceneScript (public ckpt)	0.581	0.667	—	—	—	25.9M	1.47
BIMScript (40k)	0.577	0.676	0.701	0.629	0.842	58.4M	1.14
BIMScript+ (60k)	0.576	0.669	0.699	0.639	0.840	58.5M	1.12

Adding material and condition leaves geometry accuracy unchanged. BIMScript+ is a single checkpoint that supports plain decoding, draft-and-verify and sub-bin refinement.

🏗️ Revit & IFC ingestion

BIMScript	Revit API target	IFC entity / property set
make_wall	Wall.Create (curve, level, height)	IfcWall
make_door	hosted FamilyInstance on host wall	IfcDoor + IfcRelFillsElement
make_window	hosted FamilyInstance on host wall	IfcWindow + IfcRelFillsElement
material=…	wall/family-type material parameter	IfcMaterial / IfcMaterialLayerSet
condition=…	shared parameter (custom)	custom Pset (e.g. Pset_Condition)

📦 Code release

All repositories live in the BIMScriptWorld organization. The material-passport pipeline and the Revit add-in are released; the main training code is being prepared.

Repository	Contents	Status
BIMScript	Training, evaluation and decoding	🚧 Coming soon
ASE-Material-Passport	Material-passport extraction pipeline and corpus	✅ Available
BIMScript2Revit	pyRevit add-in and IFC4 export	✅ Available

⭐ Star or watch this repository to be notified when the training code is released.

🌐 Project page

The page source is in docs/ and is served by GitHub Pages at https://BIMScriptWorld.github.io/BIMScript/. To preview it locally:

cd docs && python -m http.server 8000   # then open http://localhost:8000

📖 Citation

If you find BIMScript useful, please cite:

@misc{naikade2026bimscript,
  title         = {BIMScript: Material-Aware Structured Scene Programs for BIM Ingestion},
  author        = {Naikade, Prakash Kondibhau and Moeslund, Thomas B. and M{\o}gelmose, Andreas},
  year          = {2026},
  eprint        = {2608.21447},
  archivePrefix = {arXiv},
  primaryClass  = {cs.CV},
  url           = {https://arxiv.org/abs/2608.21447}
}

📄 License

This repository is released under the MIT License. The project page template is adapted from Nerfies under CC BY-SA 4.0.