added method to compute difference between bearings

java/com.sap.sailing.domain.test/src/com/sap/sailing/domain/test/PositionTest.java

@@ -136,4 +136,27 @@ public class PositionTest {
         assertEquals(123+345-360, sum.getDegrees(), 0.000000001);
     }
 
+    @Test
+    public void bearingDifferenceTest() {
+        Bearing b1 = new DegreeBearingImpl(340);
+        Bearing b2 = new DegreeBearingImpl(350);
+        Bearing b3 = new DegreeBearingImpl(0);
+        Bearing b4 = new DegreeBearingImpl(10);
+        Bearing b5 = new DegreeBearingImpl(20);
+        Bearing b6 = new DegreeBearingImpl(180);
+        
+        assertEquals(10., b1.getDifferenceTo(b2).getDegrees(), 0.000000001);
+        assertEquals(10., b2.getDifferenceTo(b3).getDegrees(), 0.000000001);
+        assertEquals(10., b3.getDifferenceTo(b4).getDegrees(), 0.000000001);
+        assertEquals(10., b4.getDifferenceTo(b5).getDegrees(), 0.000000001);
+
+        assertEquals(20., b2.getDifferenceTo(b4).getDegrees(), 0.000000001);
+        assertEquals(-20., b4.getDifferenceTo(b2).getDegrees(), 0.000000001);
+        assertEquals(40., b1.getDifferenceTo(b5).getDegrees(), 0.000000001);
+        assertEquals(-40., b5.getDifferenceTo(b1).getDegrees(), 0.000000001);
+
+        assertEquals(180., b3.getDifferenceTo(b6).getDegrees(), 0.000000001);
+        assertEquals(-180., b6.getDifferenceTo(b3).getDegrees(), 0.000000001);
+    }
+
 }

java/com.sap.sailing.domain/src/com/sap/sailing/domain/base/impl/AbstractBearing.java

@@ -23,6 +23,17 @@ public abstract class AbstractBearing implements Bearing {
         return new DegreeBearingImpl(newDeg);
     }
 
+    @Override
+    public Bearing getDifferenceTo(Bearing b) {
+        double diff = b.getDegrees() - getDegrees();
+        if (diff < -180) {
+            diff += 360;
+        } else if (diff > 180) {
+            diff -= 360;
+        }
+        return new DegreeBearingImpl(diff);
+    }
+
     @Override
     public String toString() {
         return ""+getDegrees()+"°";