Improve polygonize performance: single-pass tracing, JIT merge helpers, batch shapely#1010
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…s, batch shapely (#1008) Replace the two-pass _follow with a single-pass implementation using a dynamically-grown buffer. This eliminates retracing every polygon boundary a second time, which was the dominant cost for rasters with many small regions. Add @ngjit to _point_in_ring, _simplify_ring, and _signed_ring_area so the dask chunk-merge path runs compiled instead of interpreted. Use shapely.polygons() batch constructor for hole-free polygons in _to_geopandas (shapely 2.0+, with fallback for older versions).
- Buffer growth: snake-shaped polygon with >64 boundary points - JIT merge helpers: direct tests of _simplify_ring, _signed_ring_area, _point_in_ring - Dask merge: checkerboard pattern forcing many boundary merges - Geopandas batch: mixed hole-free and holed polygons through the shapely.polygons() batch path
…1008) Benchmarks showed the single-pass _follow was 15-30% slower than the original two-pass version. The buffer growth check in the inner loop adds overhead that numba doesn't optimize away, and the two-pass approach benefits from the data being in cache on the second pass. Reverted _follow to the original two-pass implementation. The JIT merge helpers (2.3-2.6x dask speedup) and batch shapely construction (1.3-1.6x geopandas speedup) are kept.
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Summary
Two internal performance changes to
polygonize. No API changes._simplify_ring,_signed_ring_area, and_point_in_ringwere plain Python loops in the dask chunk-merge path. Added@ngjitso they compile with numba._to_geopandasnow batch-constructs hole-free polygons viashapely.linearrings()+shapely.polygons()on shapely 2.0+. Polygons with holes and older shapely fall back to the scalar constructor.(An earlier commit tried replacing the two-pass
_followwith a single-pass buffer-growth approach. Benchmarks showed it was 15-30% slower -- numba already optimizes the two-pass loop well, and the buffer growth check added inner-loop overhead. Reverted.)Benchmarks
_point_in_ring10k pts_simplify_ring5k ptsTest plan
_simplify_ring,_signed_ring_area,_point_in_ringCloses #1008