Fix centroid calculation for points around the antimeridian

README.md

@@ -14,9 +14,10 @@ Please note that [geo_shape data type](https://www.elastic.co/guide/en/elasticse
 
 ## Usage
 ### Install
+Currently supported Elasticsearch version is 8.x. 
 
 Install plugin with:
-`./bin/elasticsearch-plugin install https://github.com/opendatasoft/elasticsearch-aggregation-geoclustering/releases/download/v8.19.6.1/geopoint-clustering-aggregation-8.19.6.1.zip`
+`./bin/elasticsearch-plugin install https://github.com/opendatasoft/elasticsearch-aggregation-geoclustering/releases/download/v8.19.6.2/geopoint-clustering-aggregation-8.19.6.2.zip`
 
 
 ### Quickstart

gradle.properties

@@ -1,2 +1,2 @@
 es_version = 8.19.6
-plugin_version = 8.19.6.1
+plugin_version = 8.19.6.2

src/main/java/com/opendatasoft/elasticsearch/search/aggregations/bucket/geopointclustering/InternalGeoPointClustering.java

@@ -381,8 +381,12 @@ private void computeDistance(Bucket bucket, Bucket potentialNeighbor, List<Bucke
             // Compute new weighted centroid
             double newCentroidLat = (bucket.centroid.getLat() * bucket.docCount + potentialNeighbor.centroid.getLat()
                 * potentialNeighbor.docCount) / mergedDocCount;
-            double newCentroidLon = (bucket.centroid.getLon() * bucket.docCount + potentialNeighbor.centroid.getLon()
-                * potentialNeighbor.docCount) / mergedDocCount;
+            double newCentroidLon = computeWeightedCentroidLon(
+                bucket.centroid.getLon(),
+                bucket.docCount,
+                potentialNeighbor.centroid.getLon(),
+                potentialNeighbor.docCount
+            );
             bucket.centroid = new GeoPoint(newCentroidLat, newCentroidLon);
 
             // Update document count and reduce sub-aggregations
@@ -401,6 +405,37 @@ else if (revisit != null && ratio > 0 && neighborDistance / fixedRadius < ratio)
         }
     }
 
+    /**
+     * Computes the weighted centroid longitude, handling the antimeridian (±180°) correctly.
+     * When points are on opposite sides of the antimeridian, a simple average would place
+     * the centroid on the wrong side of the globe. This method detects such cases and
+     * adjusts the calculation accordingly.
+     */
+    private static double computeWeightedCentroidLon(double lon1, long weight1, double lon2, long weight2) {
+        long totalWeight = weight1 + weight2;
+
+        // Check if points are on opposite sides of the antimeridian
+        // If the difference is greater than 180°, they cross the antimeridian
+        double lonDiff = Math.abs(lon1 - lon2);
+        if (lonDiff > 180) {
+            // Normalize longitudes to [0, 360) for calculation
+            double normalizedLon1 = lon1 < 0 ? lon1 + 360 : lon1;
+            double normalizedLon2 = lon2 < 0 ? lon2 + 360 : lon2;
+
+            // Compute weighted average in normalized space
+            double weightedLon = (normalizedLon1 * (double) weight1 + normalizedLon2 * (double) weight2) / (double) totalWeight;
+
+            // Convert back to [-180, 180] range
+            if (weightedLon > 180) {
+                weightedLon -= 360;
+            }
+            return weightedLon;
+        } else {
+            // Standard weighted average when not crossing antimeridian
+            return ((lon1 * (double) weight1 + lon2 * (double) weight2) / (double) totalWeight);
+        }
+    }
+
     @Override
     public XContentBuilder doXContentBody(XContentBuilder builder, Params params) throws IOException {
         builder.startArray(CommonFields.BUCKETS.getPreferredName());

src/yamlRestTest/resources/rest-api-spec/test/GeoPointClusteringAggregation/20_geo_clustering.yml

@@ -346,3 +346,92 @@ setup:
   - match: { aggregations.gc.buckets.0.doc_count: 3 }
   - match: { aggregations.gc.buckets.0.centroid.lat: 48.84307164698839 }
   - match: { aggregations.gc.buckets.0.centroid.lon: 2.3428986221551895 }
+
+---
+"Test that that centroid calculation with points around the antimeridian is correct (negative result)":
+  - do:
+      indices.create:
+        index: antimeridian_index
+        body:
+          mappings:
+            "properties":
+              "point":
+                "type": "geo_point"
+
+  - do:
+      index:
+        index: antimeridian_index
+        id: 1
+        body: { "point": [-179.685, 66.138] }
+
+  - do:
+      index:
+        index: antimeridian_index
+        id: 2
+        body: { "point": [179.89293, 66.138] }
+
+  - do:
+      indices.refresh:
+        index: antimeridian_index
+
+  - do:
+      search:
+        index: antimeridian_index
+        body:
+          size: 0
+          aggs:
+            gc:
+              geo_point_clustering:
+                field: point
+                zoom: 1
+
+  - match: { aggregations.gc.buckets.0.centroid.lat: 66.13799999468029 }
+  - match: { aggregations.gc.buckets.0.centroid.lon: -179.8960350221023 }
+
+
+---
+"Test that that centroid calculation with points around the antimeridian is correct (positive result)":
+  - do:
+      indices.create:
+        index: antimeridian_index
+        body:
+          mappings:
+            "properties":
+              "point":
+                "type": "geo_point"
+
+  - do:
+      index:
+        index: antimeridian_index
+        id: 1
+        body: { "point": [-179.685, 66.138] }
+
+  - do:
+      index:
+        index: antimeridian_index
+        id: 2
+        body: { "point": [179.89293, 66.138] }
+
+  - do:
+      index:
+        index: antimeridian_index
+        id: 3
+        body: { "point": [179.5, 66.138] }
+
+  - do:
+      indices.refresh:
+        index: antimeridian_index
+
+  - do:
+      search:
+        index: antimeridian_index
+        body:
+          size: 0
+          aggs:
+            gc:
+              geo_point_clustering:
+                field: point
+                zoom: 1
+
+  - match: { aggregations.gc.buckets.0.centroid.lat: 66.13799999468029 }
+  - match: { aggregations.gc.buckets.0.centroid.lon: 179.9026433005929 }