Revamp DCEL ghost edge algorithm #673
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peterstace
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The previous spanning tree approach connected arbitrary points from each component, which could create ghost lines that interfered with the geometry in problematic ways. The new algorithm: - Identifies connected components and their rightmost points - Casts horizontal rays rightward to find the closest intersection - Connects components that don't hit anything via a common vertical line This fixes several edge cases in set operations where ghost lines caused invalid DCEL construction.
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Pull request overview
This PR revamps the DCEL ghost edge algorithm by replacing the previous spanning tree approach with a new ray-casting algorithm. The new implementation is more robust and prevents ghost lines from interfering with geometries in problematic ways.
Key Changes
- Replaced spanning tree ghost line construction with a ray-casting approach that finds connected components and links them using horizontal rays
- Updated test infrastructure to support pre-noded geometries with explicit ghost lines
- Fixed several geometry operation test cases that now produce different (more accurate) results due to the improved algorithm
Reviewed changes
Copilot reviewed 8 out of 8 changed files in this pull request and generated 2 comments.
Show a summary per file
| File | Description |
|---|---|
| geom/dcel_ghosts.go | Complete rewrite of ghost line generation using ray-casting instead of spanning tree |
| geom/dcel.go | Refactored to separate geometry preparation from DCEL construction |
| geom/dcel_internal_test.go | Updated test infrastructure to accept explicit ghost lines via new input structure |
| geom/dcel_ghosts_internal_test.go | Replaced spanning tree tests with new component representative and geometry preparation tests |
| geom/internal_test.go | Added new test helper functions for internal testing |
| geom/alg_set_op_test.go | Updated expected results for set operations and added new test cases |
| internal/cmprefimpl/cmpgeos/checks.go | Removed workarounds for previously failing cases |
| CHANGELOG.md | Documented the improvement |
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peterstace
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Co-authored-by: Copilot <[email protected]>
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Description
Improves robustness of set operations (
Union,Intersection,Difference,SymmetricDifference) by revamping ghost line construction. The previousspanning tree approach could produce ghost lines that interfered with the
geometry in problematic ways. The new ray casting approach is more robust.