[GH-2830] Adds Geography dual-dispatch to ST_Centroid

[zhangfengcdt]

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 #<issue_number>

What changes were proposed in this PR?

• Adds Geography dual-dispatch to ST_Centroid — returns a Geography point for Geography inputs (planar centroid, computed in projected lon/lat space, not on the sphere).
• Use S2-spherical dispatcher S2 returns weighted (non-unit) centroids; final step normalizes via S2PAoint.normalize. Returns null if the centroid is undefined (empty input or vectors that cancel).

How was this patch tested?

• mvn clean test -pl common -am -Dtest=FunctionTest
• New Spark SQL case in GeographyFunctionTest
• mvn spotless:apply run before commit; no format violations remain.

Did this PR include necessary documentation updates?

• Yes, I have updated the documentation.

[Copilot]

Pull request overview

Adds Geography support for ST_Centroid via dual-dispatch so Geography inputs return a Geography point (planar centroid computed in projected lon/lat space), aligning Spark SQL behavior with the new common geography function set introduced in the Geography workstream.

Changes:

• Add org.apache.sedona.common.geography.Functions.centroid(Geography) and corresponding unit tests.
• Update Spark SQL ST_Centroid expression to dual-dispatch between Geometry and Geography implementations.
• Add Spark SQL integration coverage + new Geography SQL docs entry for ST_Centroid.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
spark/common/src/main/scala/org/apache/spark/sql/sedona_sql/expressions/Functions.scala	Adds Geography overload to ST_Centroid via InferredExpression dual-dispatch.
common/src/main/java/org/apache/sedona/common/geography/Functions.java	Introduces Geography centroid implementation (JTS getCentroid() + wrap to WKBGeography).
common/src/test/java/org/apache/sedona/common/Geography/FunctionTest.java	Adds unit tests for Geography centroid behavior and null handling.
spark/common/src/test/scala/org/apache/sedona/sql/geography/GeographyFunctionTest.scala	Adds Spark SQL integration test for Geography centroid (currently uses an incompatible formatter).
docs/api/sql/geography/Geography-Functions/ST_Centroid.md	Adds Geography SQL doc page for ST_Centroid (example currently uses an incompatible formatter).
docs/api/sql/geography/Geography-Functions.md	Adds ST_Centroid to the Geography functions index table.

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[jiayuasu]

@zhangfengcdt Are you sure this should go back to JTS and use planar geometry to get the centroid? Does S2 have something spherical?

[zhangfengcdt]

@zhangfengcdt Are you sure this should go back to JTS and use planar geometry to get the centroid? Does S2 have something spherical?

Yes, you're right! I switched it to S2, need a bit more work on that though - S2 returns a non-unit weighted vector, so the result is normalized via S2Point.normalize before being wrapped as SinglePointGeography.