ifc-commit/docs/ifc-extract.md

IFC Extraction — Research Notes

How to extract parts from an IFC file, for use in the ifc-commit pipeline.

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1. Core Tools

IfcOpenShell (Python)

The main toolkit. Install via pip:

pip install ifcopenshell

Open a file and select elements by type:

import ifcopenshell

model = ifcopenshell.open("model.ifc")

# All products (geometric elements)
products = model.by_type("IfcProduct")

# Specific type
walls = model.by_type("IfcWall")

# Inspect attributes
for wall in walls:
    print(wall.get_info())

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2. Extract to a New IFC File

ifcpatch — ExtractElements recipe

The cleanest high-level API for extracting a subset of elements into a new file:

import ifcopenshell
import ifcpatch

model = ifcopenshell.open("input.ifc")

result = ifcpatch.execute({
    "input": "input.ifc",
    "file": model,
    "recipe": "ExtractElements",
    "arguments": ["IfcWall"]          # or "IfcWall, IfcSlab" for multiple types
})

ifcpatch.write(result, "walls-only.ifc")

Key parameters:

Parameter	Default	Description
query	"IfcWall"	IFC type(s) to extract, comma-separated
assume_asset_uniqueness_by_name	True	Deduplicate materials/profiles by name

The recipe preserves spatial hierarchy (add_spatial_structures) and handles assets (materials, styles, profiles) via append_asset.

ifcopenshell.file.add() — Low-level copy

Copies an entity and all its dependencies recursively into another file:

import ifcopenshell

source = ifcopenshell.open("source.ifc")
target = ifcopenshell.file(schema=source.schema)

for wall in source.by_type("IfcWall"):
    target.add(wall)    # recursive deep copy

target.write("extracted.ifc")

Note: produces a valid-ish file but may need cleanup (missing spatial structure, duplicate references).

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3. Extract by GlobalId (CLI)

Using IfcConvert to filter by specific element IDs and export to another format:

IfcConvert model.ifc out.glb \
  --include attribute GlobalId 1yETHMphv6LwABqR4Pbs5g \
  --include attribute GlobalId 2xETHMphv6LwABqR0Pbs5g

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4. Spatial Decomposition

To get all sub-elements of a spatial element (building, storey, space…):

from ifcopenshell.util.element import get_decomposition

storey = model.by_type("IfcBuildingStorey")[0]
elements = get_decomposition(storey)
# → all elements contained in that storey, their parts, openings, fills

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5. Relevance for ifc-commit

Operation	Tool	Notes
Extract by type	ifcpatch ExtractElements	cleanest API
Extract by ID	IfcConvert --include	CLI, good for scripting
Deep copy to new file	ifcopenshell.file.add()	low-level, needs post-processing
Traverse spatial tree	get_decomposition()	useful for bus routing logic

Next step: insert extracted parts into a target IFC file → see ifc-insert.md.

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Sources

• IfcOpenShell — parse IFC files with Python
• ifcpatch ExtractElements recipe
• IfcOpenShell code examples — OSArch Wiki
• Splitting an IFC file into parts — SourceForge discussion
• Extracting entities from IFC — SourceForge discussion
• IfcOpenShell code examples