From cd88fbc181437f6c7288317b4d9bb34c84e19386 Mon Sep 17 00:00:00 2001
From: Jia Yu <jiayu@apache.org>
Date: Fri, 24 Jul 2026 21:09:51 -0700
Subject: [PATCH] [GH-3161] Fix RT90 transform accuracy

---
 pom.xml                                            |  2 +-
 .../apache/sedona/sql/CRSTransformProj4Test.scala  | 14 ++++++++++++++
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/pom.xml b/pom.xml
index 9f6f2af8b7d..c1484b9f3e8 100644
--- a/pom.xml
+++ b/pom.xml
@@ -96,7 +96,7 @@
         <scala-collection-compat.version>2.5.0</scala-collection-compat.version>
         <geoglib.version>1.52</geoglib.version>
         <caffeine.version>2.9.2</caffeine.version>
-        <proj4sedona.version>0.1.2</proj4sedona.version>
+        <proj4sedona.version>0.1.3</proj4sedona.version>
 
         <geotools.scope>provided</geotools.scope>
         <!-- Because it's not in Maven central, make it provided by default -->
diff --git a/spark/common/src/test/scala/org/apache/sedona/sql/CRSTransformProj4Test.scala b/spark/common/src/test/scala/org/apache/sedona/sql/CRSTransformProj4Test.scala
index 1159ebc6adc..10bec670113 100644
--- a/spark/common/src/test/scala/org/apache/sedona/sql/CRSTransformProj4Test.scala
+++ b/spark/common/src/test/scala/org/apache/sedona/sql/CRSTransformProj4Test.scala
@@ -83,6 +83,20 @@ class CRSTransformProj4Test extends TestBaseScala {
       assertEquals(4180998.88, result.getCoordinate.y, COORD_TOLERANCE)
     }
 
+    it("should apply the RT90 datum shift for EPSG:3021 to EPSG:3006 (GH-3161)") {
+      val result = sparkSession
+        .sql("SELECT ST_Transform(ST_Point(1272691.622, 6404578.16), 'epsg:3021', 'epsg:3006')")
+        .first()
+        .getAs[Geometry](0)
+
+      assertNotNull(result)
+      assertEquals(3006, result.getSRID)
+      // PostGIS reference reported in GH-3161. proj4sedona uses the proj4js
+      // RT90 Helmert parameters, so sub-metre differences from PROJ are expected.
+      assertEquals(320728.44351324334, result.getCoordinate.x, COORD_TOLERANCE)
+      assertEquals(6400228.104394391, result.getCoordinate.y, COORD_TOLERANCE)
+    }
+
     it("should transform using PROJ string") {
       val projString =
         "+proj=merc +a=6378137 +b=6378137 +lat_ts=0 +lon_0=0 +x_0=0 +y_0=0 +k=1 +units=m +no_defs"