ELK SPOrE Compaction

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Identifier: org.eclipse.elk.sporeCompaction
Meta Data Provider: options.SporeMetaDataProvider


ShrinkTree is a compaction algorithm that maintains the topology of a layout. The relocation of diagram elements is based on contracting a spanning tree.

Additional Documentation

The algorithm uses the programmatic structure of SPOrE, which stands for Structure, Processing Order, and Execution.

The Three Phases

  1. The structure phase extracts geometric information from the given layout to capture the topology that should be preserved during the subsequent adjustment of the layout.

    For this purpose, a Delaunay triangulation is implemented, which captures proximity information.

  2. Now, the processing order for the last phase is determined and represented by a tree.

  3. The execution phase traverses the previously constructed tree and applies an algorithm specific operation to each node.

The ShrinkTree Approach

The functional principle is based on a modification of an overlap removal algorithm presented by Nachmanson et al. in “Node overlap removal by growing a tree”. First, the set of vertices corresponding to the nodes’ centers is Delaunay triangulated. Second, a spanning tree of the triangulation edges is constructed. Third, the spanning tree is shrunk pulling the nodes closer together.

Use Case

Compacting the inclusion tree of a hierarchical Ptolemy model:

Supported Options

Option Default Value
Compaction Strategy CompactionStrategy.DEPTH_FIRST
Cost Function for Spanning Tree SpanningTreeCostFunction.CIRCLE_UNDERLAP
Debug Mode false
Node Spacing 8
Orthogonal Compaction false
Padding new ElkPadding(8)
Root node for spanning tree construction null
Root selection for spanning tree RootSelection.CENTER_NODE
Structure Extraction Strategy StructureExtractionStrategy.DELAUNAY_TRIANGULATION
Tree Construction Strategy TreeConstructionStrategy.MINIMUM_SPANNING_TREE
Underlying Layout Algorithm <not defined>