Handle more than one centerline for a lake (#139)

planetiler-basemap/src/main/java/com/onthegomap/planetiler/basemap/layers/WaterName.java

@@ -111,7 +111,13 @@ public class WaterName implements
       try {
         // multiple threads call this concurrently
         synchronized (this) {
-          lakeCenterlines.put(osmId, feature.worldGeometry());
+          // if we already have a centerline for this OSM_ID, then merge the existing one with this one
+          var newGeometry = feature.worldGeometry();
+          var oldGeometry = lakeCenterlines.get(osmId);
+          if (oldGeometry != null) {
+            newGeometry = GeoUtils.combine(oldGeometry, newGeometry);
+          }
+          lakeCenterlines.put(osmId, newGeometry);
         }
       } catch (GeometryException e) {
         e.log(stats, "omt_water_name_lakeline", "Bad lake centerline: " + feature);

planetiler-basemap/src/test/java/com/onthegomap/planetiler/basemap/layers/WaterNameTest.java

@@ -13,6 +13,7 @@ import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import org.junit.jupiter.api.Test;
+import org.locationtech.jts.geom.Geometry;
 
 public class WaterNameTest extends AbstractLayerTest {
 
@@ -89,6 +90,56 @@ public class WaterNameTest extends AbstractLayerTest {
     )));
   }
 
+  @Test
+  public void testWaterNameMultipleLakelines() {
+    assertFeatures(11, List.of(), process(SimpleFeature.create(
+      newLineString(0, 0, 1, 1),
+      new HashMap<>(Map.<String, Object>of(
+        "OSM_ID", -10
+      )),
+      LAKE_CENTERLINE_SOURCE,
+      null,
+      0
+    )));
+    assertFeatures(11, List.of(), process(SimpleFeature.create(
+      newLineString(2, 2, 3, 3),
+      new HashMap<>(Map.<String, Object>of(
+        "OSM_ID", -10
+      )),
+      LAKE_CENTERLINE_SOURCE,
+      null,
+      0
+    )));
+    assertFeatures(10, List.of(Map.of(
+      "_layer", "water"
+    ), Map.of(
+      "name", "waterway",
+      "name:es", "waterway es",
+
+      "_layer", "water_name",
+      "_geom",
+      new TestUtils.NormGeometry(
+        GeoUtils.latLonToWorldCoords(GeoUtils.JTS_FACTORY.createGeometryCollection(new Geometry[]{
+          newLineString(0, 0, 1, 1),
+          newLineString(2, 2, 3, 3)
+        }))),
+      "_minzoom", 9,
+      "_maxzoom", 14,
+      "_minpixelsize", "waterway".length() * 6d
+    )), process(SimpleFeature.create(
+      GeoUtils.worldToLatLonCoords(rectangle(0, Math.sqrt(1))),
+      new HashMap<>(Map.<String, Object>of(
+        "name", "waterway",
+        "name:es", "waterway es",
+        "natural", "water",
+        "water", "pond"
+      )),
+      OSM_SOURCE,
+      null,
+      10
+    )));
+  }
+
   @Test
   public void testMarinePoint() {
     assertFeatures(11, List.of(), process(SimpleFeature.create(

planetiler-core/src/main/java/com/onthegomap/planetiler/geo/GeoUtils.java

@@ -480,6 +480,23 @@ public class GeoUtils {
     }
   }
 
+  /** Combines multiple geometries into one {@link GeometryCollection}. */
+  public static Geometry combine(Geometry... geometries) {
+    List<Geometry> innerGeometries = new ArrayList<>();
+    // attempt to flatten out nested geometry collections
+    for (var geom : geometries) {
+      if (geom instanceof GeometryCollection collection) {
+        for (int i = 0; i < collection.getNumGeometries(); i++) {
+          innerGeometries.add(collection.getGeometryN(i));
+        }
+      } else {
+        innerGeometries.add(geom);
+      }
+    }
+    return innerGeometries.size() == 1 ? innerGeometries.get(0) :
+      JTS_FACTORY.createGeometryCollection(innerGeometries.toArray(Geometry[]::new));
+  }
+
   /** Helper class to sort polygons by area of their outer shell. */
   private record PolyAndArea(Polygon poly, double area) implements Comparable<PolyAndArea> {
 

planetiler-core/src/test/java/com/onthegomap/planetiler/TestUtils.java

@@ -384,7 +384,8 @@ public class TestUtils {
     result.put("_labelgrid_limit", feature.getPointLabelGridLimitAtZoom(zoom));
     result.put("_labelgrid_size", feature.getPointLabelGridPixelSizeAtZoom(zoom));
     result.put("_minpixelsize", feature.getMinPixelSizeAtZoom(zoom));
-    result.put("_type", geom instanceof Puntal ? "point" : geom instanceof Lineal ? "line" : "polygon");
+    result.put("_type", geom instanceof Puntal ? "point" : geom instanceof Lineal ? "line" :
+      geom instanceof Polygonal ? "polygon" : geom.getClass().getSimpleName());
     result.put("_numpointsattr", feature.getNumPointsAttr());
     return result;
   }

planetiler-core/src/test/java/com/onthegomap/planetiler/geo/GeoUtilsTest.java

@@ -300,4 +300,40 @@ public class GeoUtilsTest {
       }
     }
   }
+
+  @Test
+  public void testCombineEmpty() {
+    assertEquals(EMPTY_GEOMETRY, GeoUtils.combine());
+  }
+
+  @Test
+  public void testCombineOne() {
+    assertEquals(newLineString(0, 0, 1, 1), GeoUtils.combine(newLineString(0, 0, 1, 1)));
+  }
+
+  @Test
+  public void testCombineTwo() {
+    assertEquals(GeoUtils.JTS_FACTORY.createGeometryCollection(new Geometry[]{
+      newLineString(0, 0, 1, 1),
+      newLineString(2, 2, 3, 3)
+    }), GeoUtils.combine(
+      newLineString(0, 0, 1, 1),
+      newLineString(2, 2, 3, 3)
+    ));
+  }
+
+  @Test
+  public void testCombineNested() {
+    assertEquals(GeoUtils.JTS_FACTORY.createGeometryCollection(new Geometry[]{
+      newLineString(0, 0, 1, 1),
+      newLineString(2, 2, 3, 3),
+      newLineString(4, 4, 5, 5)
+    }), GeoUtils.combine(
+      GeoUtils.combine(
+        newLineString(0, 0, 1, 1),
+        newLineString(2, 2, 3, 3)
+      ),
+      newLineString(4, 4, 5, 5)
+    ));
+  }
 }