--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gnv-artifacts/src/main/java/de/intevation/gnv/math/L1Comparator.java	Fri Sep 28 12:14:00 2012 +0200
@@ -0,0 +1,78 @@
+/*
+ * Copyright (c) 2010 by Intevation GmbH
+ *
+ * This program is free software under the LGPL (>=v2.1)
+ * Read the file LGPL.txt coming with the software for details
+ * or visit http://www.gnu.org/licenses/ if it does not exist.
+ */
+
+package de.intevation.gnv.math;
+
+import com.vividsolutions.jts.geom.Coordinate;
+
+import java.util.Comparator;
+
+/**
+ * Compares two coordinates a and b by their L1(Manhattan) distance
+ * relative to a reference point r.
+ * da = L1(a, r)<br>
+ * db = L1(b, r)<br>
+ * -1 if da &lt; db, +1 if da &gt; db, 0 else.
+ * @author <a href="mailto:sascha.teichmann@intevation.de">Sascha L. Teichmann</a>
+ */
+public  class L1Comparator
+implements    Comparator
+{
+    private Coordinate ref;
+
+    /**
+     * Default constructor.
+     */
+    public L1Comparator() {
+    }
+
+    /**
+     * Constructor to create a L1Comparator with a given reference point.
+     * @param ref The reference point.
+     */
+    public L1Comparator(Coordinate ref) {
+        this.ref = ref;
+    }
+
+    /**
+     * Explicitly sets the reference point.
+     * @param ref The reference point.
+     */
+    public void setReference(Coordinate ref) {
+        this.ref = ref;
+    }
+
+    /**
+     * Compares to coordinate by their L1 distance to the reference point.
+     * @param a The first coordinate.
+     * @param b The second coordinate.
+     * @return -1 if L1(a, ref) &lt; L1(b, ref),
+     * +1 if L1(a, ref) &gt; L1(b, ref), 0 else.
+     */
+    public int compare(Object a, Object b) {
+        Coordinate pa = (Coordinate)a;
+        Coordinate pb = (Coordinate)b;
+        double da = L1(ref, pa);
+        double db = L1(ref, pb);
+        if (da < db) return -1;
+        if (da > db) return +1;
+        return 0;
+    }
+
+    /**
+     * Computes the L1 distance between two points a and b:<br>
+     * L1(a, b) = abs(a.x - b.x) + abs(a.y - b.y)
+     * @param a The first point.
+     * @param b The second point.
+     * @return The L1 distance.
+     */
+    public static double L1(Coordinate a, Coordinate b) {
+        return Math.abs(a.x - b.x) + Math.abs(a.y - b.y);
+    }
+}
+// vim:set ts=4 sw=4 si et sta sts=4 fenc=utf8 :