# IFC Extraction — Research Notes

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

---

## 1. Core Tools

### IfcOpenShell (Python)

The main toolkit. Install via pip:

```bash
pip install ifcopenshell
```

Open a file and select elements by type:

```python
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())
```

---

## 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:

```python
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:

```python
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).

---

## 3. Extract by GlobalId (CLI)

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

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

---

## 4. Spatial Decomposition

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

```python
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
```

---

## 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`.

---

## Sources

- [IfcOpenShell — parse IFC files with Python](https://thinkmoult.com/using-ifcopenshell-parse-ifc-files-python.html)
- [ifcpatch ExtractElements recipe](https://docs.ifcopenshell.org/autoapi/ifcpatch/recipes/ExtractElements/index.html)
- [IfcOpenShell code examples — OSArch Wiki](https://wiki.osarch.org/index.php?title=IfcOpenShell_code_examples)
- [Splitting an IFC file into parts — SourceForge discussion](https://sourceforge.net/p/ifcopenshell/discussion/1782718/thread/1290d16904/)
- [Extracting entities from IFC — SourceForge discussion](https://sourceforge.net/p/ifcopenshell/discussion/1782717/thread/72b5297e51/)
- [IfcOpenShell code examples](https://docs.ifcopenshell.org/ifcopenshell-python/code_examples.html)