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MarkupConstraints Slicer Module

Key Investigators

• David Allemang (Kitware Inc.)
• Jean-Christophe Fillion-Robin (Kitware Inc.)
• Lucia Cevidanes (University of Michigan)
• Maxime Gillot (University of Michigan)
• Baptiste Baquero (University of Michigan)

Acknowledgements

• Kyle Sunderland (PerkLab)

Project Description

MarkupConstraints is a Slicer module intended for Slicer extension developers to constrain and synchronize markups and control points of different nodes.

The module has been developed to support Q3DCExtension, however I intend to expand it further for reuse in other interactive tools.

Objective

1. Robust constraints between control points in different vtkMRMLMarkupNode instances
   • Support for constraining points between for example a line and fiducial markup is very limited
2. Detect dependency cycles and provide meaningful error messages
   • Slicer freezes indefinitely when updating constraints with cycles
3. Robust constraints from control points to other node types
   • Project a point to the surface of a model
4. Support saving/loading a markup node or MRML scene while preserving constraints
5. Determine the best mode of distribution and publish
   • Likely will be published on the Extension Index in “Developer Tools”
6. Create a simple interactive UI for debugging/testing purposes
   • Should allow viewing or editing existing constraints in the scene

Progress

• Created a Slicer module and logic with appropriate observers for applying constraints
• Began refining API to support arbitrary constraints and dependencies (as means to resolve #1)
• Fully resolved #1 with a robust API to define arbitrary constraints.
• Created architecture documentation and API documentation for build constraint functions.
• Created unittest suite for primary features.

Thanks to Kyle Sunderland (PerkLab) for his advice and inspiration!

Next Steps

• Implement more adaptors to enable constraints against arbitrary node types, not just control points.
• Use adaptors and node parameters/references to enable serialization with scene.
• Implement graph analysis to detect cycles and deadlocks.
• Expand constraint interface using abstract class for more extensibility.

Illustrations

Background and References

Source code is hosted in SlicerMarkupConstraints.