planetiler-openmaptiles/src/main/java/org/openmaptiles/layers/Landcover.java

/*
Copyright (c) 2021, MapTiler.com & OpenMapTiles contributors.
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  list of conditions and the following disclaimer.

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AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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Design license: CC-BY 4.0

See https://github.com/openmaptiles/openmaptiles/blob/master/LICENSE.md for details on usage
*/
package org.openmaptiles.layers;

import com.onthegomap.planetiler.FeatureCollector;
import com.onthegomap.planetiler.FeatureMerge;
import com.onthegomap.planetiler.VectorTile;
import com.onthegomap.planetiler.config.PlanetilerConfig;
import com.onthegomap.planetiler.expression.MultiExpression;
import com.onthegomap.planetiler.geo.GeometryException;
import com.onthegomap.planetiler.reader.SourceFeature;
import com.onthegomap.planetiler.stats.Stats;
import com.onthegomap.planetiler.util.Translations;
import com.onthegomap.planetiler.util.ZoomFunction;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.Set;
import org.openmaptiles.OpenMapTilesProfile;
import org.openmaptiles.generated.OpenMapTilesSchema;
import org.openmaptiles.generated.Tables;

/**
 * Defines the logic for generating map elements for natural land cover polygons like ice, sand, and forest in the
 * {@code landcover} layer from source features.
 * <p>
 * This class is ported to Java from
 * <a href="https://github.com/openmaptiles/openmaptiles/tree/master/layers/landcover">OpenMapTiles landcover sql
 * files</a>.
 */
public class Landcover implements
  OpenMapTilesSchema.Landcover,
  OpenMapTilesProfile.NaturalEarthProcessor,
  Tables.OsmLandcoverPolygon.Handler,
  OpenMapTilesProfile.FeaturePostProcessor {

  /*
   * Large ice areas come from natural earth and the rest come from OpenStreetMap at higher zoom
   * levels. At render-time, postProcess() merges polygons into larger connected area based
   * on the number of points in the original area.  Since postProcess() only has visibility into
   * features on a single tile, process() needs to pass the number of points the original feature
   * had through using a temporary "_numpoints" attribute.
   */

  public static final ZoomFunction<Number> MIN_PIXEL_SIZE_THRESHOLDS = ZoomFunction.fromMaxZoomThresholds(Map.of(
    13, 8,
    10, 4,
    9, 2
  ));
  private static final String TEMP_NUM_POINTS_ATTR = "_numpoints";
  private static final Set<String> WOOD_OR_FOREST = Set.of(
    FieldValues.SUBCLASS_WOOD,
    FieldValues.SUBCLASS_FOREST
  );
  private final MultiExpression.Index<String> classMapping;

  public Landcover(Translations translations, PlanetilerConfig config, Stats stats) {
    this.classMapping = FieldMappings.Class.index();
  }

  private String getClassFromSubclass(String subclass) {
    return subclass == null ? null : classMapping.getOrElse(Map.of(Fields.SUBCLASS, subclass), null);
  }

  @Override
  public void processNaturalEarth(String table, SourceFeature feature,
    FeatureCollector features) {
    record LandcoverInfo(String subclass, int minzoom, int maxzoom) {}
    LandcoverInfo info = switch (table) {
      case "ne_110m_glaciated_areas" -> new LandcoverInfo(FieldValues.SUBCLASS_GLACIER, 0, 1);
      case "ne_50m_glaciated_areas" -> new LandcoverInfo(FieldValues.SUBCLASS_GLACIER, 2, 4);
      case "ne_10m_glaciated_areas" -> new LandcoverInfo(FieldValues.SUBCLASS_GLACIER, 5, 6);
      case "ne_50m_antarctic_ice_shelves_polys" -> new LandcoverInfo("ice_shelf", 2, 4);
      case "ne_10m_antarctic_ice_shelves_polys" -> new LandcoverInfo("ice_shelf", 5, 6);
      default -> null;
    };
    if (info != null) {
      String clazz = getClassFromSubclass(info.subclass);
      if (clazz != null) {
        features.polygon(LAYER_NAME).setBufferPixels(BUFFER_SIZE)
          .setAttr(Fields.CLASS, clazz)
          .setAttr(Fields.SUBCLASS, info.subclass)
          .setZoomRange(info.minzoom, info.maxzoom);
      }
    }
  }

  @Override
  public void process(Tables.OsmLandcoverPolygon element, FeatureCollector features) {
    String subclass = element.subclass();
    String clazz = getClassFromSubclass(subclass);
    if (clazz != null) {
      features.polygon(LAYER_NAME).setBufferPixels(BUFFER_SIZE)
        .setMinPixelSizeOverrides(MIN_PIXEL_SIZE_THRESHOLDS)
        .setAttr(Fields.CLASS, clazz)
        .setAttr(Fields.SUBCLASS, subclass)
        .setNumPointsAttr(TEMP_NUM_POINTS_ATTR)
        .setMinZoom(7);
    }
  }

  @Override
  public List<VectorTile.Feature> postProcess(int zoom, List<VectorTile.Feature> items) throws GeometryException {
    if (zoom < 7 || zoom > 13) {
      for (var item : items) {
        item.attrs().remove(TEMP_NUM_POINTS_ATTR);
      }
      return items;
    } else { // z7-13
      // merging only merges polygons with the same attributes, so use this temporary key
      // to separate features into layers that will be merged separately
      String tempGroupKey = "_group";
      List<VectorTile.Feature> result = new ArrayList<>();
      List<VectorTile.Feature> toMerge = new ArrayList<>();
      for (var item : items) {
        Map<String, Object> attrs = item.attrs();
        Object numPointsObj = attrs.remove(TEMP_NUM_POINTS_ATTR);
        Object subclassObj = attrs.get(Fields.SUBCLASS);
        if (numPointsObj instanceof Number num && subclassObj instanceof String subclass) {
          long numPoints = num.longValue();
          if (zoom >= 10) {
            if (WOOD_OR_FOREST.contains(subclass) && numPoints < 300) {
              attrs.put(tempGroupKey, "<300");
              toMerge.add(item);
            } else { // don't merge
              result.add(item);
            }
          } else if (zoom >= 8 && zoom <= 9) {
            if (WOOD_OR_FOREST.contains(subclass)) {
              attrs.put(tempGroupKey, numPoints < 300 ? "<300" : ">300");
              toMerge.add(item);
            } else { // don't merge
              result.add(item);
            }
          } else { // zoom 7
            toMerge.add(item);
          }
        } else {
          result.add(item);
        }
      }
      var merged = FeatureMerge.mergeOverlappingPolygons(toMerge, 4);
      for (var item : merged) {
        item.attrs().remove(tempGroupKey);
      }
      result.addAll(merged);
      return result;
    }
  }
}