add gyro-based compass

mobile/src/com/cradle/iitc_mobile/compass/Compass.java

@@ -1,22 +1,37 @@
 package com.cradle.iitc_mobile.compass;
 
+import android.content.Context;
+import android.hardware.Sensor;
+import android.hardware.SensorManager;
+
 import java.util.ArrayList;
 
 public abstract class Compass
 {
+    public static Compass getDefaultCompass(final Context context) {
+        final Sensor gyro = ((SensorManager) context.getSystemService(Context.SENSOR_SERVICE))
+                .getDefaultSensor(Sensor.TYPE_GYROSCOPE);
+
+        if (gyro != null)
+            return new GyroCompass(context);
+        else
+            return new AccMagCompass(context);
+
+    }
     private final ArrayList<CompassListener> mListeners = new ArrayList<CompassListener>();
+
     private boolean mStarted = false;
 
+    protected abstract void onStart();
+
+    protected abstract void onStop();
+
     protected void publishOrientation(final float x, final float y, final float z)
     {
         for (final CompassListener listener : mListeners)
             listener.onCompassChanged(x, y, z);
     }
 
-    protected abstract void onStart();
-
-    protected abstract void onStop();
-
     public void registerListener(final CompassListener listener)
     {
         mListeners.add(listener);