bonsai-impl-clash

name	bonsai-impl-clash
description	Use when performing clash detection, interference checking, or spatial coordination in BIM models using Bonsai and IfcClash. Prevents the common mistake of running clash detection without proper element group filters (testing everything against everything). Covers clash set definition, element filtering, smart grouping of results, and BCF integration for issue tracking. Keywords: clash detection, IfcClash, interference, collision, spatial coordination, clash set, element filter, BCF integration, clash report, find collisions, elements overlap, pipes through walls.
license	MIT
compatibility	Designed for Claude Code. Requires Blender with Bonsai addon.
metadata	{"author":"OpenAEC-Foundation","version":"1.0"}

Bonsai Clash Detection Implementation

Version: Bonsai v0.8.x | IfcClash (from IfcOpenShell v0.8.x) | Blender 4.2.0+ | Python 3.11 Module path: bonsai.bim.module.clash — NEVER blenderbim.bim.module.clash Engine: IfcClash — frontend for FCL (Flexible Collision Library)

Critical Warnings

1. ALWAYS save IFC files to disk BEFORE running clash detection. IfcClash reads files from disk, NOT from Blender's in-memory model.
2. ALWAYS define BOTH Group A and Group B in every clash set, even for intra-model checks (e.g., structural vs. MEP in the same file).
3. ALWAYS use filter_groups to limit clash scope. Unfiltered detection on large models produces excessive runtime and noise.
4. ALWAYS use bim.smart_clash_group for result sets exceeding 50 clashes. Manual review of hundreds of individual clashes is impractical.
5. NEVER expect real-time clash checking. Clash detection is a batch operation — there is NO live monitoring.
6. NEVER use collision mode with allow_touching=True for detecting hard overlaps — this generates false positives where elements share surfaces. Use intersection mode instead.
7. ALWAYS specify an output path (.bcf or .json) before executing clash detection.
8. ALWAYS use bonsai.* imports. NEVER use blenderbim.* — renamed in 2024 (v0.8.0+).

---

Decision Tree: Clash Detection Mode Selection

What type of geometric conflict are you detecting?
│
├── Physical overlap (pipe through wall, duct through beam)?
│   └── Use mode = "intersection"
│       └── tolerance = 0.001 (1mm) for architectural
│       └── tolerance = 0.0001 (0.1mm) for mechanical
│
├── Surface contact (elements touching)?
│   └── Use mode = "collision"
│       └── allow_touching = False (default) for strict contact detection
│       └── allow_touching = True ONLY when surface sharing is acceptable
│
└── Proximity clearance (maintenance access, fire safety)?
    └── Use mode = "clearance"
        └── clearance = required_distance_in_meters
        └── Example: clearance = 0.3 for 300mm maintenance gap

Decision Tree: Output Format Selection

What will you do with clash results?
│
├── Share with external stakeholders (Navisworks, Solibri, BIMcollab)?
│   └── Export as .bcf
│       └── Each clash becomes a BCF topic with viewpoint
│       └── Set should_create_clash_snapshots = True for visual context
│
├── Programmatic analysis or custom reporting?
│   └── Export as .json
│       └── Contains coordinates, GlobalIds, distances
│       └── Parseable by any JSON library
│
└── Internal review within Bonsai?
    └── Export as .json
        └── Load with bim.select_ifc_clash_results
        └── Navigate clashes in 3D viewport

---

Essential Patterns

Pattern 1: Define a Clash Set

# Bonsai v0.8.x: Create and configure a clash set
import bpy

props = bpy.context.scene.BIMClashProperties

# Create a new clash set
bpy.ops.bim.add_clash_set()
clash_set = props.clash_sets[props.active_clash_set_index]

# Set detection mode
clash_set.mode = "intersection"    # "intersection" | "collision" | "clearance"
clash_set.tolerance = 0.002        # Default: 0.002m (2mm)

# Add Group A source
bpy.ops.bim.add_clash_source(group="a")
clash_set.a[0].name = "/path/to/structural.ifc"
clash_set.a[0].mode = "i"  # "a"=all, "i"=include filtered, "e"=exclude filtered

# Add Group B source
bpy.ops.bim.add_clash_source(group="b")
clash_set.b[0].name = "/path/to/mep.ifc"
clash_set.b[0].mode = "i"

Pattern 2: Run Clash Detection

# Bonsai v0.8.x: Execute clash detection
import bpy

props = bpy.context.scene.BIMClashProperties

# Set output path BEFORE execution
props.export_path = "/path/to/results.json"

# Execute clash detection
bpy.ops.bim.execute_ifc_clash()

# For BCF output with snapshots
props.should_create_clash_snapshots = True
props.export_path = "/path/to/results.bcf"
bpy.ops.bim.execute_ifc_clash()

Pattern 3: Review Clash Results

# Bonsai v0.8.x: Load and navigate clash results
import bpy

props = bpy.context.scene.BIMClashProperties

# Load results from JSON file
props.clash_results_path = "/path/to/results.json"
bpy.ops.bim.select_ifc_clash_results()

# Navigate to a specific clash (highlights pair, positions viewport)
bpy.ops.bim.select_clash(index=0)

# Access clash data
clash_set = props.clash_sets[props.active_clash_set_index]
for i, clash in enumerate(clash_set.clashes):
    print(f"Clash {i}: {clash.a_name} vs {clash.b_name}")
    print(f"  A GlobalId: {clash.a_global_id}")
    print(f"  B GlobalId: {clash.b_global_id}")
    print(f"  Type: {clash.clash_type}")

# Remove clash visualization overlay
bpy.ops.bim.hide_clash()

Pattern 4: Use IfcClash Standalone (Without Bonsai)

# IfcClash standalone: Bonsai v0.8.x / IfcOpenShell v0.8.x
import ifcclash
import json
import logging

# Configure settings
settings = ifcclash.ClashSettings()
settings.output = "/path/to/results.json"
settings.logger = logging.getLogger("IfcClash")
settings.logger.setLevel(logging.INFO)

# Define clash sets
clash_sets = [
    {
        "name": "Structural vs MEP",
        "a": [{"file": "/path/to/structural.ifc", "mode": "i", "selector": "IfcBeam"}],
        "b": [{"file": "/path/to/mep.ifc", "mode": "i", "selector": "IfcFlowSegment"}],
        "tolerance": 0.001,
        "mode": "intersection",
    }
]

# Run clash detection
clasher = ifcclash.Clasher(settings)
clasher.clash_sets = clash_sets
clasher.clash()
clasher.export()

---

Common Operations

Filter Configuration

Element filters control which elements participate in clash detection. Each ClashSource has a mode and optional filter_groups:

Filter Mode	Value	Behavior
All Elements	"a"	Include every element from the IFC file
Include	"i"	Include ONLY elements matching the selector/filter
Exclude	"e"	Include all elements EXCEPT those matching the selector/filter

Standalone IfcClash selector syntax uses IFC class names as filters:

{
    "file": "/path/to/model.ifc",
    "mode": "i",
    "selector": "IfcWall"
}

Bonsai UI filter groups use BIMFilterGroup collections on ClashSource.filter_groups for more granular control (filter by class, property, attribute).

Smart Grouping

Smart grouping clusters spatially proximate clashes using the OPTICS algorithm to reduce noise and identify systemic patterns:

# Bonsai v0.8.x: Smart clash grouping
import bpy

props = bpy.context.scene.BIMClashProperties

# Set maximum clustering distance (meters, default: 3)
props.smart_clash_grouping_max_distance = 3

# Run grouping (requires clash_results_path to be set)
bpy.ops.bim.smart_clash_group()

# Load smart groups for the active clash set
bpy.ops.bim.load_smart_groups_for_active_clash_set()

# Navigate to a specific group (selects all elements, frames viewport)
bpy.ops.bim.select_smart_group(group_index=0)

# Access group data
for group in props.smart_clash_groups:
    print(f"Group {group.number}: {len(group.global_ids)} elements")

BCF Integration

Clash results integrate directly with BCF (BIM Collaboration Format) for issue tracking:

# Bonsai v0.8.x: Clash-to-BCF workflow
import bpy

props = bpy.context.scene.BIMClashProperties

# Step 1: Run clash detection with BCF output
props.export_path = "/path/to/clashes.bcf"
props.should_create_clash_snapshots = True
bpy.ops.bim.execute_ifc_clash()

# Step 2: Load BCF results in Bonsai BCF panel
bpy.ops.bim.load_bcf_project(filepath="/path/to/clashes.bcf")

# Each clash becomes a BCF topic containing:
# - Viewpoint positioned at the clash location
# - Component references for both clashing elements (GlobalIds)
# - Metadata: clash type, severity classification

Export and Import Clash Set Configurations

# Bonsai v0.8.x: Save/restore clash set definitions
import bpy

# Export current clash set configuration to JSON
bpy.ops.bim.export_clash_sets()

# Import clash set configuration from JSON
bpy.ops.bim.import_clash_sets()

Clash Visualization in 3D Viewport

The ClashDecorator renders clash points as a viewport overlay:

• Two colored points at P1 and P2 (clash contact endpoints)
• Connecting line between P1 and P2 (when points differ)
• Text label at midpoint with clash identification
• Colors configurable via addon preferences (selected/unselected/special)
• Uses GPU shaders (UNIFORM_COLOR, POLYLINE_UNIFORM_COLOR)

# Bonsai v0.8.x: Clash visualization properties
props = bpy.context.scene.BIMClashProperties

# P1 and P2 coordinates (set by select_clash operator)
print(f"P1: {tuple(props.p1)}")
print(f"P2: {tuple(props.p2)}")
print(f"Label: {props.active_clash_text}")

---

Workflow: Complete Clash Detection Pipeline

1. Prepare Models
   ├── Save all IFC files to disk
   └── Verify file paths are absolute

2. Define Clash Sets
   ├── bpy.ops.bim.add_clash_set()
   ├── Configure mode (intersection/collision/clearance)
   ├── Set tolerance/clearance values
   ├── Add Group A sources with filters
   └── Add Group B sources with filters

3. Execute Detection
   ├── Set export_path (.json or .bcf)
   ├── Set should_create_clash_snapshots (for BCF)
   └── bpy.ops.bim.execute_ifc_clash()

4. Review Results
   ├── Load results: bpy.ops.bim.select_ifc_clash_results()
   ├── Navigate: bpy.ops.bim.select_clash(index=N)
   └── Hide overlay: bpy.ops.bim.hide_clash()

5. Group and Analyze
   ├── bpy.ops.bim.smart_clash_group()
   ├── bpy.ops.bim.load_smart_groups_for_active_clash_set()
   └── bpy.ops.bim.select_smart_group(group_index=N)

6. Report (optional)
   ├── BCF export for external collaboration
   └── JSON export for programmatic analysis

---

Operator Quick Reference

Operator	bl_idname	Purpose
AddClashSet	bim.add_clash_set	Create new clash set
RemoveClashSet	bim.remove_clash_set	Delete clash set by index
AddClashSource	bim.add_clash_source	Add IFC source to group (a/b)
RemoveClashSource	bim.remove_clash_source	Remove source from group
SelectClashSource	bim.select_clash_source	File picker for IFC source
ExecuteIfcClash	bim.execute_ifc_clash	Run clash detection engine
SelectIfcClashResults	bim.select_ifc_clash_results	Load clash results from JSON
SelectClash	bim.select_clash	Navigate to individual clash
HideClash	bim.hide_clash	Remove clash visualization
SmartClashGroup	bim.smart_clash_group	Group clashes by proximity
LoadSmartGroupsForActiveClashSet	bim.load_smart_groups_for_active_clash_set	Load saved smart groups
SelectSmartGroup	bim.select_smart_group	Select elements in smart group
ExportClashSets	bim.export_clash_sets	Export configuration to JSON
ImportClashSets	bim.import_clash_sets	Import configuration from JSON
SelectClashResults	bim.select_clash_results	Set clash results file path
SelectSmartGroupedClashesPath	bim.select_smart_grouped_clashes_path	Set smart groups file path

---

Property Reference

BIMClashProperties (on bpy.context.scene)

Property	Type	Default	Description
clash_sets	Collection[ClashSet]	—	All defined clash sets
active_clash_set_index	Int	0	Currently selected clash set
active_clash_index	Int	0	Currently selected clash
export_path	String	""	Output path for .bcf or .json
clash_results_path	String	""	Path to loaded results file
should_create_clash_snapshots	Bool	False	Generate BCF viewpoint snapshots
smart_clash_groups	Collection[SmartClashGroup]	—	Grouped clash results
active_smart_group_index	Int	0	Currently selected smart group
smart_clash_grouping_max_distance	Int	3	Max clustering distance (meters)
p1	FloatVector	(0,0,0)	First clash contact point
p2	FloatVector	(0,0,0)	Second clash contact point
active_clash_text	String	""	Label text for active clash

---

Dependencies

• bonsai-core-architecture — Three-layer architecture, IfcStore, operator pattern
• bonsai-syntax-elements — IFC element access via tool.Ifc, entity↔object mapping

Reference Links

• Complete API Signatures — All method signatures for Bonsai clash module and IfcClash engine
• Working Code Examples — End-to-end clash detection workflow examples
• Anti-Patterns — What NOT to do when implementing clash detection

Sources

• Bonsai source: src/bonsai/bonsai/bim/module/clash/ (operators, props, UI, decorator)
• Bonsai source: src/bonsai/bonsai/tool/clash.py (tool layer implementation)
• IfcClash source: src/ifcclash/ifcclash/ifcclash.py (engine)
• IfcClash docs: https://docs.ifcopenshell.org/ifcclash.html
• Bonsai docs: https://docs.bonsaibim.org