Overview

This IFC to gbXML converter is a result of research performed during my graduation project at the Eindhoven University of Technology. The converter aims to create an improved interoperability between BIM and whole-building energy analysis by translating the open exchange format IFC to a validated gbXML file format. Relationships between gbXML elements and corresponding IFC entities are created and linkages are established by iterating over multiple IFC entities.

• Author: Maarten Visschers
• Refactoring and IFC4 support: Bruno Postle

Using the converter

The current version of the converter is Python based without a GUI, with the script you are able to run the IFC-to-gbXML conversion. Supported are:

• The IFC2X3 and IFC4 schema;
• The gbXML 6.01 schema (http://www.gbxml.org/Schema_Current_GreenBuildingXML_gbXML).

Command-line usage:

ifcgbxml.py input.ifc output.xml

Python usage:

import ifcopenshell
from ifcgbxml import create_gbxml
ifc_file = ifcopenshell.open("/path/input.ifc")
root = create_gbxml(ifc_file)
root.writexml(open("/path/output.xml", "w"), indent="  ", addindent="  ", newl="\n")

What to do

The converter expects that the IFC file has sufficient data, ie:

• Each Site should have location attributes, ie. RefLatitude, RefLongitude, RefElevation and SiteAddress. RefLatitude must be correct.
• Each Building should have a BuildingAddress.
• Spatial Elements must be structured correctly, ie. a Space must be contained within a Building Storey, which must be contained within a Building, which must be contained within a Site.
• Each Space should have Qto_SpaceBaseQuantities/NetFloorArea and Qto_SpaceBaseQuantities/NetVolume quantities.
• Each Space must be bounded by 2nd Level Space Boundary relationships.
• Each Space Boundary must have a Related Building Element, planar Connection Geometry, and an Internal Or External Boundary attribute.
• Each Window and Door (or its Type) must have a U-value property in Pset_WindowCommon/ThermalTransmittance or Pset_DoorCommon/ThermalTransmittance.
• Each Window and Door (or its Type) should have a transmittance property in Pset_WindowCommon/GlazingAreaFraction or Pset_DoorCommon/GlazingAreaFraction.
• Each Building Element (or its Type) with a solid construction must have a U-value property (eg. Pset_WallCommon/ThermalTransmittance) or be constructed from a Material Layer Set with full thermal properties.
• Each Material Layer in a Material Layer Set construction must have a Thickness attribute, and each Material in a Material Layer must have an R-value property in Pset_MaterialEnergy/ThermalConductivityTemperatureDerivative.
• For metric projects, units for U-Values must be W/m²·K, and R-values must be m²·K/W. For imperial projects (ie. where the LENGTHUNIT is feet or inches), U-value units must be Btu/h·ft²·F, and R-values must be h·ft²·F/Btu.

Capabilities

• Process basic IFC building elements (e.g. walls and floors);
• Convert implicit to explicit geometric information (to comply with gbXML);
• Process IFC window and opening elements;
• Write valid information according to the official gbXML schema;
• Create gbXML files which are suitable for whole-building energy simulation in DesignBuilder;
• Include gbXML construction types with each their corresponding layer and materials;
• Include thermal properties (e.g. IFC analytical property sets);
• gbXML output is in SI units, project units are converted to SI units.

More information

For more information, please contact [email protected], or file an issue in the repository.