Add geodesic coverage mode to polygonToCellsExperimental#1178
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Adds geodesic (great-circle) polygon-to-cells support to the polygonToCellsExperimental API via a FLAG_GEODESIC_MASK flag bit. Squashed from 39 commits on geodesic_coverage branch for clean rebase onto upstream/master.
gcc -O2 inlines _ijkToHex2d and sees the uninitialized read. Initialize to zero like the non-pentagon counterpart already does.
The docs stated that only FULL and OVERLAPPING are valid when the geodesic flag is set. This contradicts the public API, which permits CENTER as well: h3api.h.in documents it, validatePolygonFlags accepts it (polygon.c), geodesicIteratorStep implements it (geodesicIterator.c), and testGeodesicPolygonToCellsExperimental.c exercises it. Only OVERLAPPING_BBOX is invalid in geodesic mode. Update the umbrella statement and all per-binding sections (Java, JavaScript, Python, Go, DuckDB) to list CENTER as valid.
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Continuation of PR #1052 |
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@ajfriend this took some time, but here we are, should be good to merge |
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coverage: 98.662% (-0.5%) from 99.176% — holoskii:geodesic_coverage into uber:master |
isaacbrodsky
requested review from
ajfriend,
dfellis,
dmitryzv,
isaacbrodsky and
nrabinowitz
July 1, 2026 16:26
dfellis
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Jul 3, 2026
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| // If the axis is nearly aligned with the normal, there's no unique | ||
| // extremum to find. | ||
| if (extremum_mag_sq < EPSILON * EPSILON) { |
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Is Epsilon squared a value above 0? I am wondering if this branch runs at all.
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Yes, far above minimum positive double value DBL_MIN = ~2.2e-308. So there can be a tiny arc exercising this branch. I created a small UT to verify it, but there is not enough value to commit it
- Fix copyright years on new files (benchmark + fuzzer geodesic) - Clarify fuzzer duplicate-run skip comment - Promote sideEps to file-scope SIDE_EPS constant in geodesicPolygon.c Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Addressed all of @dfellis commits |
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Introduce a geodesic flag for polygonToCellsExperimental that interprets
polygon edges as great-circle arcs instead of planar segments. This is
critical for accurate coverage of very large polygons spanning hundreds
or thousands of kilometers, where planar interpolation diverges
significantly from the true spherical geometry.
The implementation operates entirely on the unit sphere using 3D
Cartesian coordinates, with sphere-cap and AABB acceleration structures
for efficient cell pruning. Supports CONTAINMENT_CENTER, CONTAINMENT_FULL,
and CONTAINMENT_OVERLAPPING modes. This mode is slower than the planar
algorithm, so lower resolutions are recommended.
Note: geodesic mode rejects polygons that don't fit within a hemisphere
Key changes:
Developed at FloeDB and contributed upstream