Improve API

Author: bchapuis

baremaps-cli/src/main/java/org/apache/baremaps/cli/raster/HillShade.java

@@ -42,6 +42,7 @@
 import java.util.function.Supplier;
 import javax.imageio.ImageIO;
 import org.apache.baremaps.raster.elevation.ElevationUtils;
+import org.apache.baremaps.raster.elevation.HillshadeCalculator;
 import org.apache.baremaps.tilestore.TileCoord;
 import org.apache.baremaps.tilestore.TileStore;
 import org.apache.baremaps.tilestore.TileStoreException;
@@ -173,8 +174,9 @@ public ByteBuffer read(TileCoord tileCoord) throws TileStoreException {
             image.getHeight() + 2);
 
         var grid = ElevationUtils.imageToGrid(buffer);
-        var hillshade = org.apache.baremaps.raster.elevation.HillShade.hillShade(grid,
-            buffer.getWidth(), buffer.getHeight(), 45, 315);
+        var hillshade =
+            new HillshadeCalculator(grid, buffer.getWidth(), buffer.getHeight(), 1, true)
+                .calculate(45, 315);
 
         // Create an output image
         BufferedImage hillshadeImage =

baremaps-raster/src/main/java/org/apache/baremaps/raster/elevation/ChaikinSmoother.java

@@ -0,0 +1,87 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to you under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.baremaps.raster.elevation;
+
+import java.util.Arrays;
+import org.locationtech.jts.geom.Coordinate;
+
+public class ChaikinSmoother {
+
+  private final Coordinate[] coordinates;
+  private final double minX;
+  private final double minY;
+  private final double maxX;
+  private final double maxY;
+  private final boolean isOpen;
+
+  public ChaikinSmoother(Coordinate[] coordinates, double minX, double minY, double maxX,
+      double maxY) {
+    this.coordinates = Arrays.copyOf(coordinates, coordinates.length);
+    this.minX = minX;
+    this.minY = minY;
+    this.maxX = maxX;
+    this.maxY = maxY;
+    this.isOpen = !coordinates[0].equals(coordinates[coordinates.length - 1]);
+  }
+
+  public Coordinate[] smooth(int iterations, double factor) {
+    Coordinate[] result = isOpen
+        ? Arrays.copyOf(coordinates, coordinates.length - 1)
+        : coordinates;
+
+    double f1 = 1 - factor;
+    double f2 = factor;
+
+    // Apply the algorithm repeatedly
+    for (int n = 0; n < iterations; n++) {
+      Coordinate[] temp = new Coordinate[isOpen ? 2 * result.length - 2 : 2 * result.length];
+
+      for (int i = 0; i < result.length; i++) {
+        if (isOnBoundary(result[i]) || isOnBoundary(result[(i + 1) % result.length])) {
+          temp[2 * i] = result[i];
+          temp[2 * i + 1] = result[(i + 1) % result.length];
+        } else {
+          temp[2 * i] = new Coordinate(
+              f1 * result[i].x + f2 * result[(i + 1) % result.length].x,
+              f1 * result[i].y + f2 * result[(i + 1) % result.length].y);
+          temp[2 * i + 1] = new Coordinate(
+              f2 * result[i].x + f1 * result[(i + 1) % result.length].x,
+              f2 * result[i].y + f1 * result[(i + 1) % result.length].y);
+        }
+      }
+
+      if (isOpen) {
+        temp[0] = result[0];
+        temp[temp.length - 1] = result[result.length - 1];
+      }
+
+      result = temp;
+    }
+
+    if (!isOpen) {
+      result = Arrays.copyOf(result, result.length + 1);
+      result[result.length - 1] = result[0];
+    }
+
+    return result;
+  }
+
+  private boolean isOnBoundary(Coordinate coord) {
+    return coord.x == minX || coord.x == maxX || coord.y == minY || coord.y == maxY;
+  }
+}

baremaps-raster/src/main/java/org/apache/baremaps/raster/elevation/ContourTracer.java

@@ -18,6 +18,7 @@
 package org.apache.baremaps.raster.elevation;
 
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.List;
 import org.locationtech.jts.geom.*;
 import org.locationtech.jts.geom.util.GeometryTransformer;
@@ -55,7 +56,7 @@ public class ContourTracer {
    */
   public ContourTracer(double[] grid, int width, int height, boolean normalize,
       boolean polygonize) {
-    this.grid = grid;
+    this.grid = Arrays.copyOf(grid, grid.length);
     this.width = width;
     this.height = height;
     this.normalize = normalize;

baremaps-raster/src/main/java/org/apache/baremaps/raster/elevation/HillShade.java renamed to baremaps-raster/src/main/java/org/apache/baremaps/raster/elevation/HillshadeCalculator.java

@@ -20,64 +20,62 @@
 /**
  * Provides methods for generating hillshade effects on digital elevation models (DEMs).
  */
-public class HillShade {
+public class HillshadeCalculator {
 
   private static final double DEFAULT_SCALE = 0.1;
   private static final double ENHANCED_SCALE = 1.0;
   private static final double MIN_REFLECTANCE = 0.0;
   private static final double MAX_REFLECTANCE = 255.0;
   private static final double TWO_PI = 2 * Math.PI;
 
-  private HillShade() {
-    // Prevent instantiation
+  private final double[] dem;
+  private final int width;
+  private final int height;
+  private final double scale;
+  private final boolean isSimple;
+
+  public HillshadeCalculator(double[] dem, int width, int height, double scale, boolean isSimple) {
+    this.dem = dem;
+    this.width = width;
+    this.height = height;
+    this.scale = scale;
+    this.isSimple = isSimple;
   }
 
   /**
-   * Generates a hillshade effect on the given DEM.
+   * Generates a hillshade effect on the DEM.
    *
-   * @param dem The digital elevation model data
-   * @param width The width of the DEM
-   * @param height The height of the DEM
    * @param sunAltitude The sun's altitude in degrees
    * @param sunAzimuth The sun's azimuth in degrees
    * @return An array representing the hillshade effect
    */
-  public static double[] hillShade(double[] dem, int width, int height, double sunAltitude,
-      double sunAzimuth) {
+  public double[] calculate(double sunAltitude, double sunAzimuth) {
     validateInput(dem, width, height, sunAltitude, sunAzimuth);
-    return calculateHillShade(dem, width, height, sunAltitude, sunAzimuth, DEFAULT_SCALE, true);
+    return calculateHillshade(sunAltitude, sunAzimuth);
   }
 
   /**
    * Generates a hillshade effect on the given DEM.
    *
-   * @param dem The digital elevation model data
-   * @param width The width of the DEM
-   * @param height The height of the DEM
    * @param sunAltitude The sun's altitude in degrees
    * @param sunAzimuth The sun's azimuth in degrees
    * @return An array representing the hillshade effect
    */
-  public static double[] hillShade(double[] dem, int width, int height, double sunAltitude,
-      double sunAzimuth, double scale, boolean isSimple) {
+  public double[] calculate(double sunAltitude, double sunAzimuth, double scale, boolean isSimple) {
     validateInput(dem, width, height, sunAltitude, sunAzimuth);
-    return calculateHillShade(dem, width, height, sunAltitude, sunAzimuth, scale, isSimple);
+    return calculateHillshade(sunAltitude, sunAzimuth);
   }
 
   /**
    * Generates an enhanced hillshade effect on the given DEM.
    *
-   * @param dem The digital elevation model data
-   * @param width The width of the DEM
-   * @param height The height of the DEM
    * @param sunAltitude The sun's altitude in degrees
    * @param sunAzimuth The sun's azimuth in degrees
    * @return An array representing the enhanced hillshade effect
    */
-  public static double[] hillShadeEnhanced(double[] dem, int width, int height, double sunAltitude,
-      double sunAzimuth) {
+  public double[] calculateEnhanced(double sunAltitude, double sunAzimuth) {
     validateInput(dem, width, height, sunAltitude, sunAzimuth);
-    return calculateHillShade(dem, width, height, sunAltitude, sunAzimuth, ENHANCED_SCALE, false);
+    return calculateHillshade(sunAltitude, sunAzimuth);
   }
 
   private static void validateInput(double[] dem, int width, int height, double sunAltitude,
@@ -99,12 +97,11 @@ private static void validateInput(double[] dem, int width, int height, double su
     }
   }
 
-  private static double[] calculateHillShade(double[] dem, int width, int height,
-      double sunAltitude, double sunAzimuth, double scale, boolean isSimple) {
+  private double[] calculateHillshade(double sunAltitude, double sunAzimuth) {
     double[] hillshade = new double[dem.length];
 
     double sunAltitudeRad = Math.toRadians(sunAltitude);
-    double sunAzimuthRad = Math.toRadians(sunAzimuth + (isSimple ? 90 : 0));
+    double sunAzimuthRad = Math.toRadians(sunAzimuth + (isSimple ? 90 : 180));
     double cosSunAltitude = Math.cos(sunAltitudeRad);
     double sinSunAltitude = Math.sin(sunAltitudeRad);
 

baremaps-raster/src/test/java/org/apache/baremaps/raster/elevation/ContourRenderer.java

@@ -25,7 +25,9 @@
 import java.util.stream.Stream;
 import javax.imageio.ImageIO;
 import javax.swing.*;
+import org.locationtech.jts.geom.Coordinate;
 import org.locationtech.jts.geom.Geometry;
+import org.locationtech.jts.geom.GeometryFactory;
 
 public class ContourRenderer {
 
@@ -37,13 +39,38 @@ public static void main(String[] args) throws IOException {
         .toAbsolutePath().toFile();
     var image = ImageIO.read(path);
 
+    // Downscale the image by a factor of 16
+    image = resizeImage(image, 32, 32);
+
     // Convert the image to a grid
     double[] grid = ElevationUtils.imageToGrid(image);
 
     List<Geometry> contour =
         new ContourTracer(grid, image.getWidth(), image.getHeight(), true, true)
             .traceContours(0, 9000, 100);
 
+    // Scale the image back to its original size
+    image = resizeImage(image, image.getWidth() * 16, image.getHeight() * 16);
+
+    // Scale the contour back to its original size
+    contour = contour.stream()
+        .map(polygon -> {
+          var coordinates = Stream.of(polygon.getCoordinates())
+              .map(c -> new Coordinate(c.getX() * 16, c.getY() * 16))
+              .toArray(Coordinate[]::new);
+          return (Geometry) new GeometryFactory().createPolygon(coordinates);
+        })
+        .toList();
+
+    // Smooth the contour with the Chaikin algorithm
+    contour = contour.stream()
+        .map(polygon -> {
+          var coordinates =
+              new ChaikinSmoother(polygon.getCoordinates(), 0, 0, 512, 512).smooth(2, 0.25);
+          return (Geometry) new GeometryFactory().createPolygon(coordinates);
+        })
+        .toList();
+
     // Create a frame to display the contours
     JFrame frame = new JFrame("Contour Lines");
     frame.setSize(image.getWidth() + 20, image.getHeight() + 20);

baremaps-raster/src/test/java/org/apache/baremaps/raster/elevation/HillShadeRenderer.java

@@ -129,8 +129,8 @@ private void redrawHillshade() {
     double scale = scaleSlider.getValue() / 10.0;
     boolean isSimple = isSimpleCheckbox.isSelected();
 
-    double[] hillshade = HillShade.hillShade(grid, originalImage.getWidth(),
-        originalImage.getHeight(), sunAltitude, sunAzimuth, scale, isSimple);
+    double[] hillshade = new HillshadeCalculator(grid, originalImage.getWidth(),
+        originalImage.getHeight(), scale, isSimple).calculate(sunAltitude, sunAzimuth);
 
     BufferedImage hillshadeImage = new BufferedImage(originalImage.getWidth(),
         originalImage.getHeight(), BufferedImage.TYPE_BYTE_GRAY);

baremaps-raster/src/test/java/org/apache/baremaps/raster/elevation/HillShadeTest.java renamed to baremaps-raster/src/test/java/org/apache/baremaps/raster/elevation/HillshadeCalculatorTest.java

@@ -26,7 +26,7 @@
 import org.junit.jupiter.params.provider.Arguments;
 import org.junit.jupiter.params.provider.MethodSource;
 
-class HillShadeTest {
+class HillshadeCalculatorTest {
 
   private static final double DELTA = 1e-6;
 
@@ -43,7 +43,8 @@ void testHillShadeValidInput() {
     double sunAltitude = 45;
     double sunAzimuth = 315;
 
-    double[] result = HillShade.hillShade(dem, width, height, sunAltitude, sunAzimuth);
+    double[] result =
+        new HillshadeCalculator(dem, width, height, 1, true).calculate(sunAltitude, sunAzimuth);
 
     assertNotNull(result);
     assertEquals(dem.length, result.length);
@@ -62,7 +63,8 @@ void testHillShadeEnhancedValidInput() {
     double sunAltitude = 45;
     double sunAzimuth = 315;
 
-    double[] result = HillShade.hillShadeEnhanced(dem, width, height, sunAltitude, sunAzimuth);
+    double[] result =
+        new HillshadeCalculator(dem, width, height, 1, true).calculate(sunAltitude, sunAzimuth);
 
     assertNotNull(result);
     assertEquals(dem.length, result.length);
@@ -74,7 +76,8 @@ void testHillShadeEnhancedValidInput() {
   void testHillShadeInvalidInput(double[] dem, int width, int height, double sunAltitude,
       double sunAzimuth, Class<? extends Exception> expectedException) {
     assertThrows(expectedException,
-        () -> HillShade.hillShade(dem, width, height, sunAltitude, sunAzimuth));
+        () -> new HillshadeCalculator(dem, width, height, 1, true).calculate(sunAltitude,
+            sunAzimuth));
   }
 
   @ParameterizedTest
@@ -83,7 +86,8 @@ void testHillShadeInvalidInput(double[] dem, int width, int height, double sunAl
   void testHillShadeEnhancedInvalidInput(double[] dem, int width, int height, double sunAltitude,
       double sunAzimuth, Class<? extends Exception> expectedException) {
     assertThrows(expectedException,
-        () -> HillShade.hillShadeEnhanced(dem, width, height, sunAltitude, sunAzimuth));
+        () -> new HillshadeCalculator(dem, width, height, 1, true).calculate(sunAltitude,
+            sunAzimuth));
   }
 
   private static Stream<Arguments> provideInvalidInput() {
@@ -111,7 +115,8 @@ void testHillShadeOutputRange() {
     double sunAltitude = 45;
     double sunAzimuth = 315;
 
-    double[] result = HillShade.hillShade(dem, width, height, sunAltitude, sunAzimuth);
+    double[] result =
+        new HillshadeCalculator(dem, width, height, 1, true).calculate(sunAltitude, sunAzimuth);
 
     for (double value : result) {
       assertTrue(value >= 0 && value <= 255, "Hillshade value should be between 0 and 255");
@@ -130,7 +135,8 @@ void testHillShadeEnhancedOutputRange() {
     double sunAltitude = 45;
     double sunAzimuth = 315;
 
-    double[] result = HillShade.hillShadeEnhanced(dem, width, height, sunAltitude, sunAzimuth);
+    double[] result =
+        new HillshadeCalculator(dem, width, height, 1, true).calculate(sunAltitude, sunAzimuth);
 
     for (double value : result) {
       assertTrue(value >= 0 && value <= 255, "Hillshade value should be between 0 and 255");