use VW when rendering lines/polygons

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

@@ -6,6 +6,7 @@
 import com.onthegomap.planetiler.geo.GeoUtils;
 import com.onthegomap.planetiler.geo.GeometryException;
 import com.onthegomap.planetiler.geo.GeometryType;
+import com.onthegomap.planetiler.geo.SimplifyStrategy;
 import com.onthegomap.planetiler.reader.SourceFeature;
 import com.onthegomap.planetiler.reader.Struct;
 import com.onthegomap.planetiler.render.FeatureRenderer;
@@ -502,6 +503,9 @@ public final class Feature implements WithZoomRange<Feature>, WithAttrs<Feature>
     private double pixelToleranceAtMaxZoom = config.simplifyToleranceAtMaxZoom();
     private ZoomFunction<Number> pixelTolerance = null;
 
+    private SimplifyStrategy defaultSimplifyStrategy = SimplifyStrategy.DOUGLAS_PEUCKER;
+    private ZoomFunction<SimplifyStrategy> simplifyStrategy = null;
+
     private String numPointsAttr = null;
     private List<OverrideCommand> partialOverrides = null;
 
@@ -714,6 +718,28 @@ public double getPixelToleranceAtZoom(int zoom) {
         ZoomFunction.applyAsDoubleOrElse(pixelTolerance, zoom, defaultPixelTolerance);
     }
 
+    /**
+     * Sets the fallback line and polygon simplify method when not overriden by
+     * {@link #setSimplifyStrategyOverrides(ZoomFunction)}.
+     */
+    public FeatureCollector.Feature setSimplifyStrategy(SimplifyStrategy strategy) {
+      defaultSimplifyStrategy = strategy;
+      return this;
+    }
+
+    /** Set simplify strategy to use at different zoom levels. */
+    public FeatureCollector.Feature setSimplifyStrategyOverrides(ZoomFunction<SimplifyStrategy> overrides) {
+      simplifyStrategy = overrides;
+      return this;
+    }
+
+    /**
+     * Returns the simplification strategy for lines and polygons in tile pixels at {@code zoom}.
+     */
+    public SimplifyStrategy getSimplifyStrategyAtZoom(int zoom) {
+      return ZoomFunction.applyOrElse(simplifyStrategy, zoom, defaultSimplifyStrategy);
+    }
+
     /**
      * Sets the simplification tolerance for lines and polygons in tile pixels below the maximum zoom-level of the map.
      * <p>

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

@@ -0,0 +1,10 @@
+package com.onthegomap.planetiler.geo;
+
+public enum SimplifyStrategy {
+  RETAIN_IMPORTANT_POINTS,
+  RETAIN_EFFECTIVE_AREAS,
+  RETAIN_WEIGHTED_EFFECTIVE_AREAS;
+
+  public static final SimplifyStrategy DOUGLAS_PEUCKER = RETAIN_IMPORTANT_POINTS;
+  public static final SimplifyStrategy VISVALINGAM_WHYATT = RETAIN_EFFECTIVE_AREAS;
+}

planetiler-core/src/main/java/com/onthegomap/planetiler/render/FeatureRenderer.java

@@ -6,8 +6,10 @@
 import com.onthegomap.planetiler.geo.DouglasPeuckerSimplifier;
 import com.onthegomap.planetiler.geo.GeoUtils;
 import com.onthegomap.planetiler.geo.GeometryException;
+import com.onthegomap.planetiler.geo.SimplifyStrategy;
 import com.onthegomap.planetiler.geo.TileCoord;
 import com.onthegomap.planetiler.geo.TileExtents;
+import com.onthegomap.planetiler.geo.VWSimplifier;
 import com.onthegomap.planetiler.stats.Stats;
 import java.io.Closeable;
 import java.io.IOException;
@@ -203,14 +205,23 @@ private void renderLineOrPolygonGeometry(FeatureCollector.Feature feature, Geome
     int z, double minSize, boolean area) {
     double scale = 1 << z;
     double tolerance = feature.getPixelToleranceAtZoom(z) / 256d;
+    SimplifyStrategy strategy = feature.getSimplifyStrategyAtZoom(z);
     double buffer = feature.getBufferPixelsAtZoom(z) / 256;
     TileExtents.ForZoom extents = config.bounds().tileExtents().getForZoom(z);
 
     // TODO potential optimization: iteratively simplify z+1 to get z instead of starting with original geom each time
     // simplify only takes 4-5 minutes of wall time when generating the planet though, so not a big deal
     Geometry scaled = AffineTransformation.scaleInstance(scale, scale).transform(input);
     TiledGeometry sliced;
-    Geometry geom = DouglasPeuckerSimplifier.simplify(scaled, tolerance);
+    // TODO replace with geometry pipeline when available
+    Geometry geom = switch (strategy) {
+      case RETAIN_IMPORTANT_POINTS -> DouglasPeuckerSimplifier.simplify(scaled, tolerance);
+      // Douglas Peucker tolerance is distance off the line, and VW tolerance is area, so square what the user entered
+      // to convert from DP to VW tolerance
+      case RETAIN_EFFECTIVE_AREAS -> new VWSimplifier().setTolerance(tolerance * tolerance).transform(scaled);
+      case RETAIN_WEIGHTED_EFFECTIVE_AREAS ->
+        new VWSimplifier().setWeight(0.7).setTolerance(tolerance * tolerance).transform(scaled);
+    };
     List<List<CoordinateSequence>> groups = GeometryCoordinateSequences.extractGroups(geom, minSize);
     try {
       sliced = TiledGeometry.sliceIntoTiles(groups, buffer, area, z, extents);

planetiler-core/src/main/java/com/onthegomap/planetiler/util/ZoomFunction.java

@@ -45,6 +45,15 @@ static int applyAsIntOrElse(ZoomFunction<? extends Number> fn, int zoom, int def
     return result == null ? defaultValue : result.intValue();
   }
 
+  /** Invoke a function at a zoom level and returns {@code defaultValue} if the function or result were null. */
+  static <T> T applyOrElse(ZoomFunction<T> fn, int zoom, T defaultValue) {
+    if (fn == null) {
+      return defaultValue;
+    }
+    T result = fn.apply(zoom);
+    return result == null ? defaultValue : result;
+  }
+
   /**
    * Returns a zoom function that returns the value from the next higher key in {@code thresholds} or {@code null} if
    * over the max key.

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

@@ -18,6 +18,7 @@
 import com.onthegomap.planetiler.files.ReadableFilesArchive;
 import com.onthegomap.planetiler.geo.GeoUtils;
 import com.onthegomap.planetiler.geo.GeometryException;
+import com.onthegomap.planetiler.geo.SimplifyStrategy;
 import com.onthegomap.planetiler.geo.TileCoord;
 import com.onthegomap.planetiler.geo.TileOrder;
 import com.onthegomap.planetiler.mbtiles.Mbtiles;
@@ -429,26 +430,37 @@ void testLabelGridLimit() throws Exception {
   }
 
   @ParameterizedTest
-  @ValueSource(booleans = {false, true})
-  void testLineString(boolean anyGeom) throws Exception {
+  @CsvSource({
+    "false,RETAIN_IMPORTANT_POINTS",
+    "false,RETAIN_EFFECTIVE_AREAS",
+    "false,RETAIN_WEIGHTED_EFFECTIVE_AREAS",
+    "true,RETAIN_IMPORTANT_POINTS",
+  })
+  void testLineString(boolean anyGeom, SimplifyStrategy simplifyStrategy) throws Exception {
     double x1 = 0.5 + Z14_WIDTH / 2;
     double y1 = 0.5 + Z14_WIDTH / 2;
     double x2 = x1 + Z14_WIDTH;
     double y2 = y1 + Z14_WIDTH;
+    double ymid = (y1 + y2) / 2;
+    double xmid = (x1 + x2) / 2;
     double lat1 = GeoUtils.getWorldLat(y1);
     double lng1 = GeoUtils.getWorldLon(x1);
+    double latMid = GeoUtils.getWorldLat(ymid);
+    double lngMid = GeoUtils.getWorldLon(xmid);
     double lat2 = GeoUtils.getWorldLat(y2);
     double lng2 = GeoUtils.getWorldLon(x2);
 
     var results = runWithReaderFeatures(
       Map.of("threads", "1"),
       List.of(
-        newReaderFeature(newLineString(lng1, lat1, lng2, lat2), Map.of(
+        newReaderFeature(newLineString(lng1, lat1, lngMid, latMid, lng2, lat2), Map.of(
           "attr", "value"
         ))
       ),
       (in, features) -> (anyGeom ? features.anyGeometry("layer") : features.line("layer"))
         .setZoomRange(13, 14)
+        .setPixelTolerance(1)
+        .setSimplifyStrategy(simplifyStrategy)
         .setBufferPixels(4)
     );
 
@@ -2549,8 +2561,13 @@ void testBoundFilters() throws Exception {
     assertEquals(bboxResult.tiles, polyResult.tiles);
   }
 
-  @Test
-  void testSimplePolygon() throws Exception {
+  @ParameterizedTest
+  @CsvSource({
+    "RETAIN_IMPORTANT_POINTS",
+    "RETAIN_EFFECTIVE_AREAS",
+    "RETAIN_WEIGHTED_EFFECTIVE_AREAS",
+  })
+  void testSimplePolygon(SimplifyStrategy strategy) throws Exception {
     List<Coordinate> points = z14PixelRectangle(0, 40);
 
     var results = runWithReaderFeatures(
@@ -2561,6 +2578,8 @@ void testSimplePolygon() throws Exception {
       (in, features) -> features.polygon("layer")
         .setZoomRange(0, 14)
         .setBufferPixels(0)
+        .setPixelTolerance(1)
+        .setSimplifyStrategy(strategy)
         .setMinPixelSize(10) // should only show up z14 (40) z13 (20) and z12 (10)
     );