IFC to CityGML Conversion Using FME 2025

Automated BIM-to-GIS conversion pipeline — transform IFC building models into valid CityGML for use in 3D city platforms, digital twins, and urban analytics.

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🏗️ Overview

IFC2CITYGML is a workflow-based tool that bridges Building Information Modeling (BIM) and 3D Geospatial City Modeling by converting .ifc files into standards-compliant .gml (CityGML) format using Safe Software's FME 2025.

This project was developed during a BIM–GIS Interoperability Hackathon to demonstrate that IFC building data can be automatically translated into semantically rich CityGML outputs — without manual re-modeling.

Why does this matter?

• BIM tools (Revit, ArchiCAD, IFC-native) store detailed building geometry and metadata in IFC format.
• 3D City platforms (Cesium, 3DCityDB, QGIS, Esri) consume CityGML for urban simulation, digital twins, and smart city applications.
• There is no native bridge between these two ecosystems — this project provides one.

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✨ Features

• 🔄 Automated IFC → CityGML conversion using an FME workspace (.fmw)
• 🏢 Semantic preservation — building elements (walls, roofs, slabs, doors, windows) mapped to CityGML Building and BuildingPart modules
• 🌍 CRS / coordinate system reprojection — local IFC coordinates transformed to real-world geodetic reference systems
• 📐 LoD2 geometry output — surface-based building geometry suitable for 3D city viewers
• ✅ Valid GML output — tested against 3DCityDB import and Cesium ion tiling
• 🖼️ Visual workflow documentation — PDF screenshots of the full FME transformation pipeline

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📁 Repository Structure

IFC2CITYGML/
├── ifc-input/                # Sample IFC source files (.ifc)
├── fme-workflow/             # FME workspace file(s) (.fmw)
├── citygml-output/           # Generated CityGML output files (.gml / .xml)
├── IFC_TO_GMLscreenshots.pdf # Step-by-step FME pipeline screenshots
├── report.md                 # Detailed technical report on methodology
└── README.md

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🚀 Getting Started

Prerequisites

Tool	Version	Purpose
FME Desktop	2025+	Run the conversion workspace
An IFC file	IFC2x3 or IFC4	Your building model input
(Optional) 3DCityDB	4.x	Import and visualize CityGML output
(Optional) Cesium ion	—	Stream tiled 3D city output

Running the Conversion

1. Clone this repository

   git clone https://github.com/Sochukwumaobim/IFC2CITYGML.git
   cd IFC2CITYGML

2. Open the FME workspace

   • Launch FME Workbench 2025
   • Open fme-workflow/IFC_to_CityGML.fmw

3. Set your source IFC file

   • In the workspace, update the IFC Reader source path to your .ifc file (or use the provided sample in ifc-input/)

4. Configure the output path

   • Set the GML Writer destination to citygml-output/ or a path of your choice

5. Run the workspace

   • Click Run in FME Workbench
   • Output .gml files will be written to the configured destination

6. Validate the output (optional)

   • Import the .gml file into 3DCityDB Importer/Exporter to validate and visualize
   • Or upload to Cesium ion for web-based 3D viewing

For a detailed walkthrough of each FME transformer used, see IFC_TO_GMLscreenshots.pdf and report.md.

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🗺️ Workflow Architecture

┌─────────────┐     ┌───────────────────────┐     ┌──────────────────┐
│  IFC File   │────▶│   FME 2025 Workspace  │────▶│  CityGML (.gml)  │
│  (.ifc)     │     │                       │     │                  │
└─────────────┘     │ • IFC geometry parse  │     └──────────────────┘
                    │ • Semantic mapping    │              │
                    │ • CRS reprojection    │              ▼
                    │ • LoD2 surface gen    │     ┌──────────────────┐
                    │ • GML serialization   │     │  3DCityDB / Cesium│
                    └───────────────────────┘     │  / QGIS / ArcGIS │
                                                  └──────────────────┘

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📊 Output Format

The generated CityGML files conform to the OGC CityGML 2.0 standard and include:

• bldg:Building elements with semantic attributes from IFC IfcBuilding
• bldg:WallSurface, bldg:RoofSurface, bldg:FloorSurface geometry
• gml:Solid / gml:MultiSurface geometry representations at LoD2
• Coordinate system: configurable (default output tested with EPSG:25832 UTM zone 32N)

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🔬 Technical Report

A full technical report documenting:

• IFC schema analysis
• FME transformer selection rationale
• Geometry conversion challenges (non-planar faces, coordinate alignment)
• Validation results against CityGML schema

...is available in report.md.

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🎯 Use Cases

• Digital Twin development — feed converted building models into city-scale digital twins
• Urban planning — integrate BIM data into GIS platforms for urban analytics
• Smart city applications — enrich CityGML city models with BIM-level detail
• Academic research — BIM–GIS interoperability, semantic data translation, LoD conversion studies
• Infrastructure projects — connect design-phase BIM data with operational GIS systems

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🤝 Contributing

Contributions are welcome! If you've extended the FME workflow, added support for additional IFC element types, or improved CRS handling, please:

1. Fork the repository
2. Create a feature branch (git checkout -b feature/improve-lod3-support)
3. Commit your changes
4. Open a Pull Request with a clear description

Please see CONTRIBUTING.md if available, or open an Issue to discuss ideas first.

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📚 Related Resources

• OGC CityGML Standard
• BuildingSMART IFC Standard
• Safe Software FME Documentation
• 3DCityDB Open Source City Database
• Cesium ion Platform

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📄 License

This project is licensed under the MIT License — see the LICENSE file for details.

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🏆 Acknowledgements

Built during a BIM–GIS Interoperability Hackathon to demonstrate automated, standards-compliant conversion between IFC and CityGML using the FME platform.

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Keywords: IFC to CityGML, BIM GIS interoperability, FME IFC conversion, CityGML LoD2, 3DCityDB import, digital twin BIM, IFC GML transformation, building model conversion, urban digital twin, smart city GIS