Add CubicBezierCurve control point generation

Author: dr-jts

modules/app/src/main/java/org/locationtech/jtstest/function/CreateShapeFunctions.java

@@ -364,6 +364,22 @@ public static Geometry bezierCurveControl(Geometry geom, Geometry controlPoints)
     return CubicBezierCurve.bezierCurve(geom, controlPoints);
   }
 
+  @Metadata(description="Get the generated control points for a Bezier curve")
+  public static Geometry bezierControl(Geometry geom, 
+      @Metadata(title="Alpha (curveness)")
+      double alpha) {
+    return CubicBezierCurve.controlPoints(geom, alpha);
+  }
+  
+  @Metadata(description="Get the generated control points for a Bezier curve with a skew")
+  public static Geometry bezierControlSkew(Geometry geom, 
+      @Metadata(title="Alpha (curveness)")
+      double alpha,
+    @Metadata(title="Skew factor")
+    double skew) {
+    return CubicBezierCurve.controlPoints(geom, alpha, skew);
+  }
+  
   public static Geometry nGon(Geometry g, 
       @Metadata(title="Num sides")
       int sides) {

modules/core/src/main/java/org/locationtech/jts/shape/CubicBezierCurve.java

@@ -68,6 +68,37 @@ public static Geometry bezierCurve(Geometry geom, double alpha, double skew) {
     return curve.getResult();
   }
 
+  /**
+   * Gets a linear geometry containing the generated control points 
+   * for the Bezier curve defined by the segments of the input and a parameter
+   * controlling how curved the result should be, with a skew factor
+   * affecting the curve shape at each vertex.
+   * 
+   * @param geom the geometry defining the curve
+   * @param alpha curvedness parameter (0 is linear, 1 is round, >1 is increasingly curved)
+   * @return the line(s) containing the control points
+   */
+  public static Geometry controlPoints(Geometry geom, double alpha) {
+    CubicBezierCurve curve = new CubicBezierCurve(geom, alpha);
+    return curve.getControlPoints();
+  }
+  
+  /**
+   * Gets a linear geometry containing the generated control points 
+   * for the Bezier curve defined by the segments of the input and a parameter
+   * controlling how curved the result should be, with a skew factor
+   * affecting the curve shape at each vertex.
+   * 
+   * @param geom the geometry defining the curve
+   * @param alpha curvedness parameter (0 is linear, 1 is round, >1 is increasingly curved)
+   * @param skew the skew parameter (0 is none, positive skews towards longer side, negative towards shorter
+   * @return the line(s) containing the control points
+   */
+  public static Geometry controlPoints(Geometry geom, double alpha, double skew) {
+    CubicBezierCurve curve = new CubicBezierCurve(geom, alpha, skew);
+    return curve.getControlPoints();
+  }
+  
   /**
    * Creates a geometry of linearized Cubic Bezier Curves
    * defined by the segments of the input
@@ -157,7 +188,7 @@ public static Geometry bezierCurve(Geometry geom, Geometry controlPoints) {
    */
   public Geometry getResult() {
     bezierCurvePts = new Coordinate[numVerticesPerSegment];
-    interpolationParam = computeIterpolationParameters(numVerticesPerSegment);
+    interpolationParam = computeInterpolationParameters(numVerticesPerSegment);
 
     return GeometryMapper.flatMap(inputGeom, 1, new GeometryMapper.MapOp() {
 
@@ -175,6 +206,35 @@ public Geometry map(Geometry geom) {
     });
   }
 
+  /**
+   * Gets the computed control points for the Bezier curve.
+   * 
+   * @return a linear geometry holding the control points
+   */
+  public Geometry getControlPoints() {
+    bezierCurvePts = new Coordinate[numVerticesPerSegment];
+    interpolationParam = computeInterpolationParameters(numVerticesPerSegment);
+
+    return GeometryMapper.flatMap(inputGeom, 1, new GeometryMapper.MapOp() {
+      
+      @Override
+      public Geometry map(Geometry geom) {
+        if (geom instanceof LineString) {
+          Coordinate[] control = controlPoints(geom.getCoordinates(), false);
+          return geom.getFactory().createLineString(control);
+        }
+        if (geom instanceof Polygon ) {
+          Polygon poly = (Polygon) geom;
+          Coordinate[] control = controlPoints(poly.getExteriorRing().getCoordinates(), true);
+          //TODO: include holes as well
+          return geom.getFactory().createLineString(control);
+        } 
+        //-- Points
+        return geom.copy();
+      }
+    });
+  }
+  
   private LineString bezierLine(LineString ls) {
     //-- can't curve a single segment
     if (ls.getNumPoints() <= 2)
@@ -278,7 +338,7 @@ private void addCurve(Coordinate p0, Coordinate p1,
    * @param alpha determines the curviness
    * @return the control point array
    */
-  private Coordinate[] controlPoints(Coordinate[] coords, boolean isRing, double alpha, double skew) {
+  private static Coordinate[] controlPoints(Coordinate[] coords, boolean isRing, double alpha, double skew) {
     int N = coords.length;
     int start = 1; 
     int end = N - 1;
@@ -351,7 +411,7 @@ private Coordinate[] controlPoints(Coordinate[] coords, boolean isRing, double a
    * @param coords
    * @param ctrl
    */
-  private void setLineEndControlPoints(Coordinate[] coords, Coordinate[] ctrl) {
+  private static void setLineEndControlPoints(Coordinate[] coords, Coordinate[] ctrl) {
     int N = ctrl.length;
     ctrl[0] = mirrorControlPoint(ctrl[1], coords[1], coords[0]);
     ctrl[N - 1] = mirrorControlPoint(ctrl[N - 2], 
@@ -436,7 +496,7 @@ private void cubicBezier(final Coordinate p0,
    * @param n number of vertices
    * @return array of double[4] holding the parameter values
    */
-  private static double[][] computeIterpolationParameters(int n) {
+  private static double[][] computeInterpolationParameters(int n) {
     double[][] param = new double[n][4];
     for (int i = 0; i < n; i++) {
       double t = (double) i / (n - 1);

modules/core/src/test/java/org/locationtech/jts/shape/CubicBezierCurveTest.java

@@ -46,6 +46,11 @@ public void testAlphaRightAngle() {
         "LINESTRING (30 40, 30.1 41.1, 30.2 42.1, 30.5 43.1, 30.9 44, 31.4 44.9, 32 45.8, 32.7 46.6, 33.4 47.3, 34.2 48, 35.1 48.6, 36 49.1, 36.9 49.5, 37.9 49.8, 38.9 49.9, 40 50, 41.1 49.9, 42.1 49.8, 43.1 49.5, 44 49.1, 44.9 48.6, 45.8 48, 46.6 47.3, 47.3 46.6, 48 45.8, 48.6 44.9, 49.1 44, 49.5 43.1, 49.8 42.1, 49.9 41.1, 50 40)");
   }
 
+  public void testAlphaRightAngleControl() {
+    checkControl("LINESTRING (30 40, 40 50, 50 40)", 1,
+        "LINESTRING (30 45.3, 34.7 50, 45.3 50, 50 45.3)");
+  }
+
   public void testAlphaRightZigzag() {
     checkCurve("LINESTRING (10 10, 20 19, 30 10, 40 20)", 1,
         "LINESTRING (10 10, 10.2 11, 10.4 11.9, 10.8 12.9, 11.2 13.7, 11.7 14.6, 12.3 15.3, 13 16, 13.7 16.7, 14.5 17.3, 15.3 17.8, 16.2 18.2, 17.1 18.5, 18 18.8, 19 18.9, 20 19, 20.9 18.9, 21.8 18.6, 22.5 18.1, 23.1 17.4, 23.7 16.6, 24.2 15.8, 24.8 14.9, 25.2 14, 25.8 13.1, 26.3 12.3, 26.9 11.5, 27.5 10.9, 28.2 10.4, 29.1 10.1, 30 10, 31 10.1, 32 10.3, 33 10.6, 33.9 11, 34.8 11.5, 35.7 12.1, 36.5 12.8, 37.2 13.5, 37.9 14.3, 38.5 15.2, 39 16.1, 39.4 17, 39.7 18, 39.9 19, 40 20)");
@@ -69,6 +74,20 @@ private void checkCurve(String wkt, double alpha, String wktExpected) {
     checkEqual(expected, actual, 0.5);
   }
 
+  private void checkControl(String wkt, double alpha, String wktExpected) {
+    Geometry geom = read(wkt);
+    Geometry actual = CubicBezierCurve.controlPoints(geom, alpha);
+    Geometry expected = read(wktExpected);
+    checkEqual(expected, actual, 0.5);
+  }
+  
+  private void checkControl(String wkt, double alpha, double skew, String wktExpected) {
+    Geometry geom = read(wkt);
+    Geometry actual = CubicBezierCurve.controlPoints(geom, alpha, skew);
+    Geometry expected = read(wktExpected);
+    checkEqual(expected, actual, 0.5);
+  }
+  
   private void checkCurve(String wkt, String wktCtrl, String wktExpected) {
     Geometry geom = read(wkt);
     Geometry ctrl = read(wktCtrl);