Fix buffer union unbuffer exceptions

planetiler-core/src/main/java/com/onthegomap/planetiler/FeatureMerge.java

@@ -29,6 +29,7 @@
 import org.locationtech.jts.geom.Polygon;
 import org.locationtech.jts.geom.Polygonal;
 import org.locationtech.jts.geom.TopologyException;
+import org.locationtech.jts.geom.util.GeometryFixer;
 import org.locationtech.jts.index.strtree.STRtree;
 import org.locationtech.jts.operation.buffer.BufferOp;
 import org.locationtech.jts.operation.buffer.BufferParameters;
@@ -323,7 +324,7 @@ public static List<VectorTile.Feature> mergeNearbyPolygons(List<VectorTile.Featu
             // spinning for a very long time on very dense tiles.
             // TODO use some heuristic to choose bufferUnbuffer vs. bufferUnionUnbuffer based on the number small
             //      polygons in the group?
-            merged = bufferUnionUnbuffer(buffer, polygonGroup);
+            merged = bufferUnionUnbuffer(buffer, polygonGroup, stats);
           } else {
             merged = buffer(buffer, GeoUtils.createGeometryCollection(polygonGroup));
           }
@@ -411,7 +412,7 @@ public static Collection<List<VectorTile.Feature>> groupByAttrs(
    * Merges nearby polygons by expanding each individual polygon by {@code buffer}, unioning them, and contracting the
    * result.
    */
-  private static Geometry bufferUnionUnbuffer(double buffer, List<Geometry> polygonGroup) throws GeometryException {
+  static Geometry bufferUnionUnbuffer(double buffer, List<Geometry> polygonGroup, Stats stats) {
     /*
      * A simpler alternative that might initially appear faster would be:
      *
@@ -433,10 +434,11 @@ private static Geometry bufferUnionUnbuffer(double buffer, List<Geometry> polygo
     try {
       merged = union(merged);
     } catch (TopologyException e) {
-      throw new GeometryException("buffer_union_failure", "Error unioning buffered polygons", e)
-        .addGeometryDetails("original", GeoUtils.createGeometryCollection(polygonGroup))
-        .addDetails(() -> "buffer: " + buffer)
-        .addGeometryDetails("buffered", GeoUtils.createGeometryCollection(buffered));
+      // buffer result is sometimes invalid, which makes union throw so fix
+      // it and try again (see #700)
+      stats.dataError("buffer_union_unbuffer_union_failed");
+      merged = GeometryFixer.fix(merged);
+      merged = union(merged);
     }
     merged = unbuffer(buffer, merged);
     return merged;

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

@@ -10,7 +10,9 @@
 import com.onthegomap.planetiler.geo.GeometryException;
 import com.onthegomap.planetiler.geo.GeometryType;
 import com.onthegomap.planetiler.mbtiles.Mbtiles;
+import com.onthegomap.planetiler.stats.Stats;
 import java.io.IOException;
+import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
 import java.util.Map;
@@ -20,11 +22,14 @@
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.CsvSource;
+import org.junit.jupiter.params.provider.ValueSource;
 import org.locationtech.jts.geom.Geometry;
 import org.locationtech.jts.geom.GeometryCollection;
 import org.locationtech.jts.geom.LineString;
 import org.locationtech.jts.geom.Point;
 import org.locationtech.jts.geom.Polygon;
+import org.locationtech.jts.io.ParseException;
+import org.locationtech.jts.io.WKBReader;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -853,4 +858,27 @@ void removePointsOutsideBufferMultiPoints() throws GeometryException {
       )
     );
   }
+
+  @ParameterizedTest
+  @ValueSource(strings = {
+    "/issue_700/exception_1.wkb",
+    "/issue_700/exception_2.wkb",
+    "/issue_700/exception_3.wkb",
+    "/issue_700/exception_4.wkb",
+    "/issue_700/exception_5.wkb",
+    "/issue_700/exception_6.wkb",
+    "/issue_700/exception_7.wkb",
+    "/issue_700/exception_8.wkb",
+    "/issue_700/exception_9.wkb",
+  })
+  void testIssue700BufferUnionUnbufferFailure(String path) throws IOException, ParseException {
+    try (var is = getClass().getResource(path).openStream()) {
+      GeometryCollection collection = (GeometryCollection) new WKBReader().read(is.readAllBytes());
+      List<Geometry> geometries = new ArrayList<>();
+      for (int i = 0; i < collection.getNumGeometries(); i++) {
+        geometries.add(collection.getGeometryN(i));
+      }
+      FeatureMerge.bufferUnionUnbuffer(0.5, geometries, Stats.inMemory());
+    }
+  }
 }