IfcGref Web-Based Application

Overview

This Flask-based application serves the purpose of georeferencing IFC (Industry Foundation Classes) files, which are commonly used in the context of Building Information Modeling (BIM) data exchange. To accomplish georeferencing, the application leverages the IFCMapConversion entity in IFC4, which facilitates the updating of data and the conversion from a local Coordinate Reference System (CRS), often referred to as the engineering coordinate system, into the coordinate reference system of the underlying map (Projected CRS). It's accessible at https://ifcgref.bk.tudelft.nl.

Prerequisites

Before running the application, make sure you have the following prerequisites installed on your system:

• Python 3
• Flask
• ifcopenshell
• pyproj
• pint
• numpy
• scipy
• pandas
• shapely

You can install these dependencies using pip:

pip install Flask ifcopenshell pyproj pint numpy scipy pandas shapely

Supported IFC versions

Coordinate operations become accessible starting from IFC 4. For earlier versions like the widely utilized IFC2x3, the utilization of Property sets (Pset) is employed to enable georeferencing. The table below outlines the supported versions:

Version	Name
4.3.2.0	IFC 4.3 ADD2
4.0.2.0	IFC4 ADD2 TC1
4.0.2.1	IFC4 ADD2
4.0.2.0	IFC4 ADD1
4.0.0.0	IFC4
2.3.0.1	IFC2x3 TC1
2.3.0.0	IFC2x3

Usage

1. Clone this repository or download the application files to your local machine.

2. Navigate to the project directory in your terminal.

3. Run the Flask application:

python app.py

This will start the Flask development server.

4. Access the application in your web browser by going to http://localhost:5000/.
5. Follow the on-screen instructions to upload an IFC file and specify the target EPSG code.
6. The application will georeference the IFC file and provide details about the process.
7. You can then visualize the georeferenced IFC file on the map and download it.

Configuration

The application reads deployment settings from environment variables:

Variable	Default	Purpose
IFCGREF_SECRET_KEY	random per process	Flask session signing key. Set this in production so sessions survive restarts.
IFCGREF_DEBUG	off	Set to 1, true, yes, or on only for local debugging.
IFCGREF_MAX_UPLOAD_MB	250	Maximum IFC upload size in megabytes.
IFCGREF_WORKERS	2	Number of background IFC processing workers.
IFCGREF_UPLOAD_RETENTION_DAYS	30	Number of days to keep uploaded IFC files and model state. Use 0 to disable cleanup.
IFCGREF_JOB_RETENTION_DAYS	7	Number of days to keep background job status files. Use 0 to disable cleanup.
IFCGREF_MAPTILER_KEY	empty	Optional MapTiler API key used by the MapTiler layers.
IFCGREF_HOST	127.0.0.1	Host used when running python app.py.
IFCGREF_PORT	5000	Port used when running python app.py.
IFCGREF_DESKTOP	off	Enables local desktop mode. The desktop launcher sets this automatically.
IFCGREF_DATA_DIR	current directory	Desktop/local data directory. The desktop launcher defaults to %LOCALAPPDATA%\IfcGref.

For local development you can also put these values in a .env file next to app.py. The .env file is ignored by git and should be used for local keys such as IFCGREF_MAPTILER_KEY.

Desktop App

IfcGref can also be distributed as a desktop app that still runs in the user's browser. The desktop launcher starts the Flask tool on 127.0.0.1, opens the browser automatically, and stores uploads locally on the user's machine. In desktop mode there is no Flask upload size limit unless IFCGREF_MAX_UPLOAD_MB is explicitly set.

To run it locally:

python desktop_app.py

To build a Windows package:

.\desktop\build_windows.ps1 -Version 3.0

To build a native macOS package, run this on a Mac:

bash ./desktop/build_macos.sh 3.0

To build the portable macOS launcher package from any OS:

python desktop/build_macos_portable.py 3.0

The build scripts create platform zips in desktop_dist/. The home page has separate Windows and Mac download buttons; each button serves the newest package for that platform from desktop_dist/.

File Structure

• app.py: The main Flask application file.
• desktop_app.py: Local desktop-browser launcher.
• desktop/: Desktop packaging instructions and scripts.
• static/: Directory to store static files (e.g., GeoJSON output).
• templates/: HTML templates for the web interface.
• uploads/: Directory to temporarily store uploaded IFC files.
• envelop/: Directory to EnvelopExtractor exe files and temporary store shell produced files.

Workflow

HTTP request

For streamlined handling of incoming IFC files by developers, whether they are georeferenced or not, a specialized section called "devs" is available at https://ifcgref.bk.tudelft.nl/devs. Developers can engage with this section by submitting an HTTP request containing the IFC file, and in response, the server provides them with a corresponding response.

Sample of HTTP request from the devs section using a python script:

import requests

url = 'https://ifcgref.bk.tudelft.nl/devs'
file_path = './00.ifc'


data = {
    'file': ('00.ifc', open(file_path, 'rb'))
}


# Make a POST request to the /devs route with the data
response = requests.post(url, files=data)

# Print the response content
print(response.text)

Credits

• This application uses the Flask web framework for the user interface.
• It leverages the ifcopenshell library for working with IFC files.
• Georeferencing is performed using pyproj for coordinate transformations.
• The optimization is performed using SciPy and in particular scipy.optimize.least_squares function.
• For the vizualization feature IfcEnvelopeExtractor is used for generating the roof-print of the 3D BIM model.

Acknowledgments

This project has received funding from the European Union’s Horizon Europe programme under Grant Agreement No.101058559 (CHEK: Change toolkit for digital building permit).

References

BuildingSMART. IFC Specifications database. https://technical.buildingsmart.org/standards/ifc/ifc-schema-specifications/

BuildingSMART Australasia (2020). User Guide for Geo-referencing in IFC, version 2.0. https://www.buildingsmart.org/wp-content/uploads/2020/02/User-Guide-for-Geo-referencing-in-IFC-v2.0.pdf

https://github.com/stijngoedertier/georeference-ifc#readme