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

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);

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(