Mercurial > dive4elements > gnv-client

annotate gnv-artifacts/src/main/java/de/intevation/gnv/math/L1Comparator.java @ 1051:8f836fb6f592

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Introduced an epsilon (750ms) to be more tolerant while comparing two data objects (issue286). gnv-artifacts/trunk@1125 c6561f87-3c4e-4783-a992-168aeb5c3f6f
author Ingo Weinzierl <ingo.weinzierl@intevation.de>
date Tue, 25 May 2010 17:46:28 +0000
parents a645bd23c1c8
children f953c9a559d8
rev   line source
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1 package de.intevation.gnv.math;
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2
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3 import com.vividsolutions.jts.geom.Coordinate;
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4
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5 import java.util.Comparator;
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6
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7 /**
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8 * Compares two coordinates a and b by their L1(Manhattan) distance
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9 * relative to a reference point r.
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10 * da = L1(a, r)<br>
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11 * db = L1(b, r)<br>
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12 * -1 if da &lt; db, +1 if da &gt; db, 0 else.
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13 * @author <a href="mailto:sascha.teichmann@intevation.de">Sascha L. Teichmann</a>
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14 */
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15 public class L1Comparator
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16 implements Comparator
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17 {
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18 private Coordinate ref;
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19
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20 /**
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21 * Default constructor.
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22 */
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23 public L1Comparator() {
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24 }
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25
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26 /**
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27 * Constructor to create a L1Comparator with a given reference point.
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28 * @param ref The reference point.
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29 */
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30 public L1Comparator(Coordinate ref) {
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31 this.ref = ref;
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32 }
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33
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34 /**
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35 * Explicitly sets the reference point.
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36 * @param ref The reference point.
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37 */
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38 public void setReference(Coordinate ref) {
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39 this.ref = ref;
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40 }
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42 /**
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43 * Compares to coordinate by their L1 distance to the reference point.
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44 * @param a The first coordinate.
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45 * @param b The second coordinate.
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46 * @return -1 if L1(a, ref) &lt; L1(b, ref),
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47 * +1 if L1(a, ref) &gt; L1(b, ref), 0 else.
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48 */
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49 public int compare(Object a, Object b) {
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50 Coordinate pa = (Coordinate)a;
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51 Coordinate pb = (Coordinate)b;
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52 double da = L1(ref, pa);
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53 double db = L1(ref, pb);
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54 if (da < db) return -1;
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55 if (da > db) return +1;
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56 return 0;
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57 }
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58
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59 /**
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60 * Computes the L1 distance between two points a and b:<br>
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61 * L1(a, b) = abs(a.x - b.x) + abs(a.y - b.y)
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62 * @param a The first point.
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63 * @param b The second point.
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64 * @return The L1 distance.
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65 */
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66 public static double L1(Coordinate a, Coordinate b) {
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67 return Math.abs(a.x - b.x) + Math.abs(a.y - b.y);
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68 }
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69 }
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70 // vim:set ts=4 sw=4 si et sta sts=4 fenc=utf8 :
http://dive4elements.wald.intevation.org