Shamos-Hoey simple polygon detection bug fix

Author: bosborn

src/main/java/mil/nga/sf/Point.java

@@ -218,6 +218,42 @@ public boolean isSimple() {
 		return true;
 	}
 
+	/**
+	 * Indicates if x values are equal
+	 * 
+	 * @param point
+	 *            point to compare
+	 * @return true if x is equal
+	 * @since 2.2.1
+	 */
+	public boolean equalsX(Point point) {
+		return Double.doubleToLongBits(x) == Double.doubleToLongBits(point.x);
+	}
+
+	/**
+	 * Indicates if y values are equal
+	 * 
+	 * @param point
+	 *            point to compare
+	 * @return true if y is equal
+	 * @since 2.2.1
+	 */
+	public boolean equalsY(Point point) {
+		return Double.doubleToLongBits(y) == Double.doubleToLongBits(point.y);
+	}
+
+	/**
+	 * Indicates if x and y values are equal
+	 * 
+	 * @param point
+	 *            point to compare
+	 * @return true if x and y are equal
+	 * @since 2.2.1
+	 */
+	public boolean equalsXY(Point point) {
+		return equalsX(point) && equalsY(point);
+	}
+
 	/**
 	 * {@inheritDoc}
 	 */
@@ -252,9 +288,7 @@ public boolean equals(Object obj) {
 				return false;
 		} else if (!m.equals(other.m))
 			return false;
-		if (Double.doubleToLongBits(x) != Double.doubleToLongBits(other.x))
-			return false;
-		if (Double.doubleToLongBits(y) != Double.doubleToLongBits(other.y))
+		if (!equalsXY(other))
 			return false;
 		if (z == null) {
 			if (other.z != null)

src/main/java/mil/nga/sf/util/sweep/ShamosHoey.java

@@ -110,12 +110,21 @@ public static boolean simplePolygon(List<LineString> rings) {
 			if (ringCopyPoints.size() >= 3) {
 				Point first = ringCopyPoints.get(0);
 				Point last = ringCopyPoints.get(ringCopyPoints.size() - 1);
-				if (first.getX() == last.getX()
-						&& first.getY() == last.getY()) {
+				if (first.equalsXY(last)) {
 					ringCopyPoints.remove(ringCopyPoints.size() - 1);
 				}
 			}
 
+			// Remove duplicate consecutive points
+			for (int j = 0; j < ringCopyPoints.size() - 1; j++) {
+				Point point = ringCopyPoints.get(j);
+				Point next = ringCopyPoints.get(j + 1);
+				if (point.equalsXY(next)) {
+					ringCopyPoints.remove(j + 1);
+					j--;
+				}
+			}
+
 			// Verify enough ring points
 			if (ringCopyPoints.size() < 3) {
 				simple = false;

src/main/java/mil/nga/sf/util/sweep/SweepLine.java

@@ -23,50 +23,56 @@ public class SweepLine {
 	 */
 	private class SegmentComparator implements Comparator<Segment> {
 
-		/**
-		 * Current sweep x value
-		 */
-		private double x;
-
-		/**
-		 * Set the current sweep x value
-		 * 
-		 * @param x
-		 *            x value
-		 */
-		public void setX(double x) {
-			this.x = x;
-		}
-
 		/**
 		 * {@inheritDoc}
 		 */
 		@Override
 		public int compare(Segment segment1, Segment segment2) {
 
-			double y1 = yValueAtX(segment1, x);
-			double y2 = yValueAtX(segment2, x);
-
-			int compare;
-			if (y1 < y2) {
-				compare = -1;
-			} else if (y2 < y1) {
-				compare = 1;
-			} else if (segment1.getRing() < segment2.getRing()) {
-				compare = -1;
-			} else if (segment2.getRing() < segment1.getRing()) {
-				compare = 1;
-			} else if (segment1.getEdge() < segment2.getEdge()) {
-				compare = -1;
-			} else if (segment2.getEdge() < segment1.getEdge()) {
-				compare = 1;
-			} else {
-				compare = 0;
+			int compare = 0;
+
+			if (segment1 != segment2) {
+
+				Point lp1 = segment1.getLeftPoint();
+				Point rp1 = segment1.getRightPoint();
+				Point lp2 = segment2.getLeftPoint();
+				Point rp2 = segment2.getRightPoint();
+
+				if (lp1.getX() <= lp2.getX()) {
+					double s = isLeft(segment1, lp2);
+					if (s != 0) {
+						compare = comparison(s > 0);
+					} else {
+						if (lp1.equalsX(rp1)) { // Vertical line
+							compare = comparison(lp1.getY() < lp2.getY());
+						} else {
+							compare = comparison(isLeft(segment1, rp2) > 0);
+						}
+					}
+				} else {
+					double s = isLeft(segment2, lp1);
+					if (s != 0) {
+						compare = comparison(s < 0);
+					} else {
+						compare = comparison(isLeft(segment2, rp1) < 0);
+					}
+				}
 			}
 
 			return compare;
 		}
 
+		/**
+		 * Get the comparison value
+		 * 
+		 * @param left
+		 *            left comparison result
+		 * @return -1 if left, 1 if right
+		 */
+		private int comparison(boolean left) {
+			return left ? -1 : 1;
+		}
+
 	}
 
 	/**
@@ -111,23 +117,16 @@ public Segment add(Event event) {
 		Segment segment = createSegment(event);
 
 		// Add to the tree
-		comparator.setX(event.getPoint().getX());
 		tree.add(segment);
 
 		// Update the above and below pointers
 		Segment next = tree.higher(segment);
-		if (next == null) {
-			next = tree.first();
-		}
 		Segment previous = tree.lower(segment);
-		if (previous == null) {
-			previous = tree.last();
-		}
-		if (next != segment) {
+		if (next != null) {
 			segment.setAbove(next);
 			next.setBelow(segment);
 		}
-		if (previous != segment) {
+		if (previous != null) {
 			segment.setBelow(previous);
 			previous.setAbove(segment);
 		}
@@ -200,7 +199,7 @@ public boolean intersect(Segment segment1, Segment segment2) {
 
 		boolean intersect = false;
 
-		if (segment1 != null && segment2 != null && segment1 != segment2) {
+		if (segment1 != null && segment2 != null) {
 
 			int ring1 = segment1.getRing();
 			int ring2 = segment2.getRing();
@@ -244,7 +243,6 @@ public void remove(Segment segment) {
 
 		boolean removed = tree.remove(segment);
 		if (!removed) {
-			comparator.setX(segment.getLeftPoint().getX());
 			removed = tree.remove(segment);
 		}
 
@@ -264,28 +262,6 @@ public void remove(Segment segment) {
 
 	}
 
-	/**
-	 * Get the segment y value at the x location by calculating the line slope
-	 * 
-	 * @param segment
-	 *            segment
-	 * @param x
-	 *            current point x value
-	 * @return segment y value
-	 */
-	private double yValueAtX(Segment segment, double x) {
-
-		Point left = segment.getLeftPoint();
-		Point right = segment.getRightPoint();
-
-		double m = (right.getY() - left.getY()) / (right.getX() - left.getX());
-		double b = left.getY() - (m * left.getX());
-
-		double y = (m * x) + b;
-
-		return y;
-	}
-
 	/**
 	 * XY order of two points
 	 *