min zoom for pixel size

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

@@ -703,6 +703,27 @@ public Feature setAttrWithMinzoom(String key, Object value, int minzoom) {
       return setAttr(key, ZoomFunction.minZoom(minzoom, value));
     }
 
+    /**
+     * Sets the value for {@code key} only at zoom levels where the feature is at least {@code minPixelSize} pixels in
+     * size.
+     */
+    public Feature setAttrWithMinSize(String key, Object value, double minPixelSize) {
+      return setAttrWithMinzoom(key, value, getMinZoomForPixelSize(minPixelSize));
+    }
+
+    /**
+     * Sets the value for {@code key} so that it always shows when {@code zoom_level >= minZoomToShowAlways} but only
+     * shows when {@code minZoomIfBigEnough <= zoom_level < minZoomToShowAlways} when it is at least
+     * {@code minPixelSize} pixels in size.
+     * <p>
+     * If you need more flexibility, use {@link #getMinZoomForPixelSize(double)} directly.
+     */
+    public Feature setAttrWithMinSize(String key, Object value, double minPixelSize, int minZoomIfBigEnough,
+      int minZoomToShowAlways) {
+      return setAttrWithMinzoom(key, value,
+        Math.clamp(getMinZoomForPixelSize(minPixelSize), minZoomIfBigEnough, minZoomToShowAlways));
+    }
+
     /**
      * Inserts all key/value pairs in {@code attrs} into the set of attribute to emit on the output feature at or above
      * {@code minzoom}.
@@ -766,9 +787,20 @@ public double getSourceFeaturePixelSizeAtZoom(int zoom) {
       try {
         return source.size() * (256 << zoom);
       } catch (GeometryException e) {
-        e.log(stats, "point_get_size_failure", "Error getting min size for point from geometry " + source.id());
+        e.log(stats, "source_feature_pixel_size_at_zoom_failure",
+          "Error getting source feature pixel size at zoom from geometry " + source.id());
         return 0;
       }
     }
+
+    /** Returns the minimum zoom level at which this feature is at least {@code pixelSize} pixels large. */
+    public int getMinZoomForPixelSize(double pixelSize) {
+      try {
+        return GeoUtils.minZoomForPixelSize(source.size(), pixelSize);
+      } catch (GeometryException e) {
+        e.log(stats, "min_zoom_for_size_failure", "Error getting min zoom for size from geometry " + source.id());
+        return config.maxzoom();
+      }
+    }
   }
 }

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

@@ -1,6 +1,7 @@
 package com.onthegomap.planetiler.geo;
 
 import com.onthegomap.planetiler.collection.LongLongMap;
+import com.onthegomap.planetiler.config.PlanetilerConfig;
 import com.onthegomap.planetiler.stats.Stats;
 import java.util.ArrayList;
 import java.util.List;
@@ -51,6 +52,7 @@ public class GeoUtils {
   public static final double WORLD_CIRCUMFERENCE_METERS = Math.PI * 2 * WORLD_RADIUS_METERS;
   private static final double RADIANS_PER_DEGREE = Math.PI / 180;
   private static final double DEGREES_PER_RADIAN = 180 / Math.PI;
+  private static final double LOG2 = Math.log(2);
   /**
    * Transform web mercator coordinates where top-left corner of the planet is (0,0) and bottom-right is (1,1) to
    * latitude/longitude coordinates.
@@ -534,6 +536,18 @@ public static Geometry combine(Geometry... geometries) {
       JTS_FACTORY.createGeometryCollection(innerGeometries.toArray(Geometry[]::new));
   }
 
+  /**
+   * For a feature of size {@code worldGeometrySize} (where 1=full planet), determine the minimum zoom level at which
+   * the feature appears at least {@code minPixelSize} pixels large.
+   * <p>
+   * The result will be clamped to the range [0, {@link PlanetilerConfig#MAX_MAXZOOM}].
+   */
+  public static int minZoomForPixelSize(double worldGeometrySize, double minPixelSize) {
+    double worldPixels = worldGeometrySize * 256;
+    return Math.clamp((int) Math.ceil(Math.log(minPixelSize / worldPixels) / LOG2), 0,
+      PlanetilerConfig.MAX_MAXZOOM);
+  }
+
   /** 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/PlanetilerTests.java

@@ -87,6 +87,8 @@ class PlanetilerTests {
   private static final double Z13_WIDTH = 1d / Z13_TILES;
   private static final int Z12_TILES = 1 << 12;
   private static final double Z12_WIDTH = 1d / Z12_TILES;
+  private static final int Z11_TILES = 1 << 11;
+  private static final double Z11_WIDTH = 1d / Z11_TILES;
   private static final int Z4_TILES = 1 << 4;
   private static final Polygon WORLD_POLYGON = newPolygon(
     worldCoordinateList(
@@ -2434,6 +2436,74 @@ void testCentroidWithLineMinSize() throws Exception {
     ), results.tiles);
   }
 
+  @Test
+  void testAttributeMinSizeLine() throws Exception {
+    List<Coordinate> points = z14CoordinatePixelList(0, 4, 40, 4);
+
+    var results = runWithReaderFeatures(
+      Map.of("threads", "1"),
+      List.of(
+        newReaderFeature(newLineString(points), Map.of())
+      ),
+      (in, features) -> features.line("layer")
+        .setZoomRange(11, 14)
+        .setBufferPixels(0)
+        .setAttrWithMinSize("a", "1", 10)
+        .setAttrWithMinSize("b", "2", 20)
+        .setAttrWithMinSize("c", "3", 40)
+        .setAttrWithMinSize("d", "4", 40, 0, 13) // should show up at z13 and above
+    );
+
+    assertEquals(Map.ofEntries(
+      newTileEntry(Z11_TILES / 2, Z11_TILES / 2, 11, List.of(
+        feature(newLineString(0, 0.5, 5, 0.5), Map.of())
+      )),
+      newTileEntry(Z12_TILES / 2, Z12_TILES / 2, 12, List.of(
+        feature(newLineString(0, 1, 10, 1), Map.of("a", "1"))
+      )),
+      newTileEntry(Z13_TILES / 2, Z13_TILES / 2, 13, List.of(
+        feature(newLineString(0, 2, 20, 2), Map.of("a", "1", "b", "2", "d", "4"))
+      )),
+      newTileEntry(Z14_TILES / 2, Z14_TILES / 2, 14, List.of(
+        feature(newLineString(0, 4, 40, 4), Map.of("a", "1", "b", "2", "c", "3", "d", "4"))
+      ))
+    ), results.tiles);
+  }
+
+  @Test
+  void testAttributeMinSizePoint() throws Exception {
+    List<Coordinate> points = z14CoordinatePixelList(0, 4, 40, 4);
+
+    var results = runWithReaderFeatures(
+      Map.of("threads", "1"),
+      List.of(
+        newReaderFeature(newLineString(points), Map.of())
+      ),
+      (in, features) -> features.centroid("layer")
+        .setZoomRange(11, 14)
+        .setBufferPixels(0)
+        .setAttrWithMinSize("a", "1", 10)
+        .setAttrWithMinSize("b", "2", 20)
+        .setAttrWithMinSize("c", "3", 40)
+        .setAttrWithMinSize("d", "4", 40, 0, 13) // should show up at z13 and above
+    );
+
+    assertEquals(Map.ofEntries(
+      newTileEntry(Z11_TILES / 2, Z11_TILES / 2, 11, List.of(
+        feature(newPoint(2.5, 0.5), Map.of())
+      )),
+      newTileEntry(Z12_TILES / 2, Z12_TILES / 2, 12, List.of(
+        feature(newPoint(5, 1), Map.of("a", "1"))
+      )),
+      newTileEntry(Z13_TILES / 2, Z13_TILES / 2, 13, List.of(
+        feature(newPoint(10, 2), Map.of("a", "1", "b", "2", "d", "4"))
+      )),
+      newTileEntry(Z14_TILES / 2, Z14_TILES / 2, 14, List.of(
+        feature(newPoint(20, 4), Map.of("a", "1", "b", "2", "c", "3", "d", "4"))
+      ))
+    ), results.tiles);
+  }
+
   @Test
   void testBoundFiltersFill() throws Exception {
     var polyResultz8 = runForBoundsTest(8, 8, "polygon", TestUtils.pathToResource("bottomrightearth.poly").toString());

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

@@ -447,4 +447,30 @@ void testSnapAndFixIssue546_3() throws GeometryException, ParseException {
     assertTrue(result.isValid());
     assertFalse(result.contains(point));
   }
+
+  @ParameterizedTest
+  @CsvSource({
+    "1,0,0",
+    "1,10,0",
+    "1,255,0",
+
+    "0.5,0,0",
+    "0.5,128,0",
+    "0.5,129,1",
+    "0.5,256,1",
+
+    "0.25,0,0",
+    "0.25,128,1",
+    "0.25,129,2",
+    "0.25,256,2",
+  })
+  void minZoomForPixelSize(double worldGeometrySize, double minPixelSize, int expectedMinZoom) {
+    assertEquals(expectedMinZoom, GeoUtils.minZoomForPixelSize(worldGeometrySize, minPixelSize));
+  }
+
+  @Test
+  void minZoomForPixelSizesAtZ9_10() {
+    assertEquals(10, GeoUtils.minZoomForPixelSize(3.1 / (256 << 10), 3));
+    assertEquals(9, GeoUtils.minZoomForPixelSize(6.1 / (256 << 10), 3));
+  }
 }