[GH-2527] Implement GeoPandas concave_hull

[chay0112]

Did you read the Contributor Guide?

• Yes, I have read the Contributor Rules and Contributor Development Guide

Is this PR related to a ticket?

• Yes, and the PR name follows the format [GH-XXX] my subject. Closes Geopandas: Implement concave_hull #2527

What changes were proposed in this PR?

• Implement concave_hull functionality

How was this patch tested?

• Included unit and parity tests

Did this PR include necessary documentation updates?

• Yes, I have updated the documentation.

[chay0112]

Hi @petern48

I'm encountering a test failure in our Sedona/GeoPandas parity suite for concave_hull(Passing in my local). The error is due to the vertex order of polygons returned by Sedona and GeoPandas being different, even though the polygons are geometrically identical. Our current comparison uses equals_exact(assert_geometry_almost_equal), which might be sensitive to vertex order:

=========================== short test summary info ============================ FAILED tests/geopandas/test_match_geopandas_series.py::TestMatchGeopandasSeries::test_concave_hull - ValueError: Geometry equality check failed for POLYGON ((1 4, 3 4, 4 4, 3 1, 4 0, 0 0, 1 1, 0 4, 1 4)) and POLYGON ((1 4, 3 4, 4 4, 4 0, 3 1, 0 0, 1 1, 0 4, 1 4))

https://github.com/apache/sedona/actions/runs/19687051539/job/56394868966?pr=2529

Would it be acceptable to change our comparison from equals_exact to equals for polygons, so that we check geometric equality rather than strict vertex order? Or is there a recommended workaround for this situation, or something I might be missing in our test setup?

Thank you for your guidance!

[petern48]

Would it be acceptable to change our comparison from equals_exact to equals for polygons, so that we check geometric equality rather than strict vertex order? Or is there a recommended workaround for this situation, or something I might be missing in our test setup?

The issue is not whether we're using equals_exact() or equals(). If you give it a try, you'll see that the comparison fails either way. Despite the name, equals_exact is actually more lenient, since it supports a tolerance parameter.

Script to test using equals instead

import shapely
geom1 = shapely.wkt.loads("POLYGON ((1 4, 3 4, 4 4, 3 1, 4 0, 0 0, 1 1, 0 4, 1 4))")
geom2 = shapely.wkt.loads("POLYGON ((1 4, 3 4, 4 4, 4 0, 3 1, 0 0, 1 1, 0 4, 1 4))")
print(geom1.equals(geom2))  # False
print(geom1.equals_exact(geom2, 0.000001))  # False

Images to visualize the different results

As you can see above, these geometries actually are different. Why this is happening, I'm not sure. It could either be a bug in Sedona's function or a difference in algorithms or edge case behaviors. If it's a significant bug, we may want to hold off. If it's a reasonable difference in behavior that's still correct, we can add a note in the docs and merge this anyway. Either way, we need to understand what's happening before merging. I encourage you to investigate, though you're not obligated to, of course, and can continue with something else instead.

[Copilot]

Pull request overview

Implements and hardens concave_hull parity for the Sedona GeoPandas API by refining Python-side typing/docs and expanding unit/parity test coverage (including allow_holes=True cases) to better match GeoPandas behavior.

Changes:

• Expanded GeoPandas parity tests to cover multiple ratio values and an allow_holes=True fixture designed to avoid JTS/GEOS triangulation tie ambiguity.
• Added a deterministic allow_holes=True concave hull expectation in GeoSeries unit tests.
• Added a return type annotation for GeoSeries.concave_hull and improved end-user docstring content.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
python/tests/geopandas/test_match_geopandas_series.py	Extends parity tests for concave_hull across ratio values and validates allow_holes=True behavior.
python/tests/geopandas/test_geoseries.py	Adds a dedicated allow_holes=True concave hull assertion with an asymmetric point set.
python/sedona/spark/geopandas/geoseries.py	Adds GeoSeries return type annotation for concave_hull.
python/sedona/spark/geopandas/base.py	Updates concave_hull docstring (but currently contains a misleading algorithm/parameter explanation).

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