IfcClash is both a CLI utility and library that lets you perform clash detection on one or more IFC models. Clashes are defined in terms of clash sets with filters using the IFC query syntax.

Source installation

  1. Install IfcOpenShell

  2. Install hppfcl

  3. Optionally install bcf (needed for BCF reports of results)

  4. Clone the source code.

  5. cd /path/to/IfcOpenShell/src/ifcclash

Here is a minimal example of how to use IfcPatch as a Python module or CLI utility:

$ python -m ifcclash -h

usage: __main__.py [-h] [-o OUTPUT] input

Clashes geometry between two IFC files

positional arguments:
  input                 A JSON dataset describing a series of clashsets

  -h, --help            show this help message and exit
  -o OUTPUT, --output OUTPUT
                        The JSON diff file to output. Defaults to output.json

Instructions on what clashes to perform are structured in terms of clash sets. Each clash set contains instructions of collisions that we want to perform, and can be named so it is easy to distinguish. A typical name would be “Structure and Pipes”, to describe that we are are detecting collisions between structural elements and pipes.

Each clash set may include two groups of objects, named A and B. This tells IfcClash to attempt to find collisions between any object in group A with any object in group B. Group A is mandatory, but group B is optional. If group B is not provided, IfcClash will detect all clashes within objects of group A.

Within group A or B, you may define one or more data sources of objects. A data source must include a path to the IFC file which the objects come from. You may also optionally provide a filter to only include or exclude certain objects. If no filter is provided, then all objects will be used to detect collisions.

Here’s a sample JSON description of a single clash set, with both groups defined with data sources.

        "name": "Clash Set A",
        "a": [
                "file": "/path/to/one.ifc"
        "b": [
                "file": "/path/to/two.ifc",
                "selector": ".IfcWall",
                "mode": "i"

Once your have your JSON description of your clashes, usage is like any other CLI app.

$ ifcclash clash_sets.json
$ cat output.json

Here is a minimal example of how to use IfcClash as a library:

import sys
import json
import logging
import ifcclash

settings = ClashSettings()
settings.output = "output.json"
settings.logger = logging.getLogger("Clash")
handler = logging.StreamHandler(sys.stdout)
ifc_clasher = Clasher(settings)
with open(args.input, "r") as clash_sets_file:
    ifc_clasher.clash_sets = json.loads(clash_sets_file.read())

You can also alias it to a command:

$ alias ifcclash='python -m ifcclash'

Alternatively, you can package it as an executable.

$ python make.py
$ ./dist/ifcclash