Model Comparison

Compare different versions of a model and automatically detect changes.

Overview

Model comparison analyzes two models and detects changes in geometry and properties. Results are displayed with color coding in the 3D viewer.

Starting a Comparison

1. Load at least two models into the project
2. Click on → "Model Comparison" in the toolbar
3. The comparison dialog opens
4. Select:
   • Reference Model (Base) - Older version/original model
   • Comparison Model (Current) - Newer version/modified model
5. Optional: Adjust the tolerance (default: 10mm)
6. Click "Start Comparison"

Model Naming

Name your models with clear version numbers (e.g., "Architecture_v1.ifc", "Architecture_v2.ifc") for easier identification.

Tolerance Settings

The tolerance determines when a geometry change is detected:

• 1mm - Very strict, detects smallest changes
• 10mm - Standard, detects relevant changes
• 50mm - Tolerant, only larger changes
• 100mm - Very tolerant, only significant changes

AABB-based

The comparison is based on Axis-Aligned Bounding Boxes (AABB). Small detail changes within the AABB may not be detected.

Comparison Results

After the comparison, the system shows:

Color Coding in Viewer

Differences are color-coded in the 3D viewer:

Color	Icon	Meaning
Green		Added - new in the current model
Red		Removed - no longer present
Yellow		Modified - geometry or properties changed
Orange		Both - present in both models
Gray		Unchanged - no modifications

Results List

The list shows all changes with:

• Element Name - Name of the element
• IFC Type - Classification (IfcWall, IfcSlab, etc.)
• GUID - Unique ID
• Change Type - Added/Removed/Modified
• Category - Type of change:
  • AABB - Geometry change only (size/position)
  • Properties - Property change only (attributes)
  • Both - Geometry and properties changed

Viewing Change Details

Click on an element in the list:

1. The element is highlighted in the viewer
2. The camera zooms to it (fly-to animation)
3. The properties panel shows details

For Modified Elements

For modified elements you can see:

Geometry Changes:

• Position moved (X/Y/Z delta)
• Size changed (bounding box difference)
• Shape modified

Property Changes:

• New properties added
• Properties removed
• Values changed (Before → After)

The view shows a Before/After comparison with:

• Old Value (from reference model)
• New Value (from comparison model)
• Property Set Name (e.g., Pset_LILASp)
• Property Key (e.g., ComponentName)

Filtering by Change Type

In the comparison dialog, you can filter results by change type:

• ✅ Added - Show only new elements
• ✅ Removed - Show only deleted elements
• ✅ Modified - Show only modified elements
• ✅ Unchanged - Also show unchanged elements

Additional Filter Options

Use the Explorer (left panel) for detailed filtering by IFC type, element name, or GlobalId. See Explorer Panel.

Spatial Matching

When an element has a new GUID but is at the same position:

• The system recognizes this as "Modified" instead of "Removed + Added"
• The old GUID is stored
• In the details dialog you will see: GUID changed: [old-GUID] → [new-GUID]

This is useful when:

• The model was re-exported
• GUIDs changed due to a software update
• Elements were replaced (same position)

Closing the Comparison

To exit comparison mode:

1. Click "End Comparison"
2. Or in the toolbar: → (click again)
3. The color coding is removed
4. The viewer returns to normal mode

Best Practices

Consistent Models

• Only compare models with the same basis (e.g., both from Revit)
• Use consistent export settings
• Ensure matching coordinate systems

Performance

For very large models (>10,000 elements):

• Limit the comparison to specific floors
• Use a higher tolerance (50-100mm)
• Hide unimportant element types (e.g., IfcSpace)

Limitations

• Comparison is based on AABB (Axis-Aligned Bounding Box)
• Very fine detail changes may not be detected
• Pure rotations without position change are difficult to detect

Use Cases

Tracking Planning Iterations

1. Compare Version 1 with Version 2
2. See which walls were moved
3. Check if windows were added/removed

Quality Control

1. Compare discipline models (Architecture vs. MEP)
2. Verify that changes were correctly incorporated
3. Identify missing or additional elements

Change Management

1. Document all changes
2. Export reports for stakeholders
3. Use the data for impact analyses

See Also

• Manage Models - Upload model versions
• 3D Viewer - Navigation and filtering
• Collision Detection - Detect intersections
• Advanced Filters - Filter results by type