Improve coarse locations.

Fix a couple of bugs, and modify the behavior of the random offset.

The random offset now slowly changes over time, to mitigate against
applications averaging out the offset over time while at a
grid boundary.

Change-Id: Iecffff29145b8c2b30d1eca1662cf9d3e8cff756

Author: Nick Pelly

location/java/android/location/LocationRequest.java

@@ -195,20 +195,6 @@ public float getSmallestDisplacement() {
         return mSmallestDisplacement;
     }
 
-    /** @hide */
-    public LocationRequest applyCoarsePermissionRestrictions() {
-        switch (mQuality) {
-            case ACCURACY_FINE:
-                mQuality = ACCURACY_BLOCK;
-                break;
-        }
-        // cap fastest interval to 6 seconds
-        if (mFastestInterval < 6 * 1000) mFastestInterval = 6 * 1000;
-        // cap requested interval to 1 minute
-        if (mInterval < 60 * 1000) mInterval = 60 * 1000;
-        return this;
-    }
-
     private static void checkInterval(long millis) {
         if (millis < 0) {
             throw new IllegalArgumentException("invalid interval: " + millis);

services/java/com/android/server/LocationManagerService.java

@@ -47,7 +47,6 @@
 import android.os.IBinder;
 import android.os.Looper;
 import android.os.Message;
-import android.os.Parcelable;
 import android.os.PowerManager;
 import android.os.Process;
 import android.os.RemoteException;
@@ -64,6 +63,7 @@
 import com.android.server.location.GeocoderProxy;
 import com.android.server.location.GeofenceManager;
 import com.android.server.location.GpsLocationProvider;
+import com.android.server.location.LocationFudger;
 import com.android.server.location.LocationProviderInterface;
 import com.android.server.location.LocationProviderProxy;
 import com.android.server.location.MockProvider;
@@ -110,19 +110,6 @@ public class LocationManagerService extends ILocationManager.Stub implements Obs
 
     private static final int MSG_LOCATION_CHANGED = 1;
 
-    // Accuracy in meters above which a location is considered coarse
-    private static final double COARSE_ACCURACY_M = 100.0;
-    private static final String EXTRA_COARSE_LOCATION = "coarseLocation";
-
-    private static final int APPROXIMATE_METERS_PER_DEGREE_AT_EQUATOR = 111000;
-
-    /**
-     * Maximum latitude of 1 meter from the pole.
-     * This keeps cosine(MAX_LATITUDE) to a non-zero value;
-     */
-    private static final double MAX_LATITUDE =
-            90.0 - (1.0 / APPROXIMATE_METERS_PER_DEGREE_AT_EQUATOR);
-
     // Location Providers may sometimes deliver location updates
     // slightly faster that requested - provide grace period so
     // we don't unnecessarily filter events that are otherwise on
@@ -137,6 +124,7 @@ public class LocationManagerService extends ILocationManager.Stub implements Obs
     private final Object mLock = new Object();
 
     // --- fields below are final after init() ---
+    private LocationFudger mLocationFudger;
     private GeofenceManager mGeofenceManager;
     private PowerManager.WakeLock mWakeLock;
     private PackageManager mPackageManager;
@@ -221,6 +209,7 @@ private void init() {
             loadProvidersLocked();
         }
         mGeofenceManager = new GeofenceManager(mContext);
+        mLocationFudger = new LocationFudger();
 
         // Register for Network (Wifi or Mobile) updates
         IntentFilter filter = new IntentFilter();
@@ -907,7 +896,22 @@ private String checkPermissionAndRequest(LocationRequest request) {
         String perm = checkPermission();
 
         if (ACCESS_COARSE_LOCATION.equals(perm)) {
-            request.applyCoarsePermissionRestrictions();
+             switch (request.getQuality()) {
+                 case LocationRequest.ACCURACY_FINE:
+                     request.setQuality(LocationRequest.ACCURACY_BLOCK);
+                     break;
+                 case LocationRequest.POWER_HIGH:
+                     request.setQuality(LocationRequest.POWER_LOW);
+                     break;
+             }
+             // throttle fastest interval
+             if (request.getFastestInterval() < LocationFudger.FASTEST_INTERVAL_MS) {
+                 request.setFastestInterval(LocationFudger.FASTEST_INTERVAL_MS);
+             }
+        }
+        // throttle interval if its faster than the fastest interval
+        if (request.getInterval () < request.getFastestInterval()) {
+            request.setInterval(request.getFastestInterval());
         }
         return perm;
     }
@@ -1075,7 +1079,7 @@ public Location getLastLocation(LocationRequest request) {
             if (ACCESS_FINE_LOCATION.equals(perm)) {
                 return location;
             } else {
-                return getCoarseLocationExtra(location);
+                return mLocationFudger.getOrCreate(location);
             }
         }
     }
@@ -1291,11 +1295,8 @@ private void handleLocationChangedLocked(Location location, boolean passive) {
         LocationProviderInterface p = mProvidersByName.get(provider);
         if (p == null) return;
 
-        // Add the coarse location as an extra, if not already present
-        Location coarse = getCoarseLocationExtra(location);
-        if (coarse == null) {
-            coarse = addCoarseLocationExtra(location);
-        }
+        // Add the coarse location as an extra
+        Location coarse = mLocationFudger.getOrCreate(location);
 
         // Update last known locations
         Location lastLocation = mLastLocation.get(provider);
@@ -1660,106 +1661,6 @@ public void clearTestProviderStatus(String provider) {
         }
     }
 
-    private static double wrapLatitude(double lat) {
-         if (lat > MAX_LATITUDE) lat = MAX_LATITUDE;
-         if (lat < -MAX_LATITUDE) lat = -MAX_LATITUDE;
-         return lat;
-    }
-
-    private static double wrapLongitude(double lon) {
-        if (lon >= 180.0) lon -= 360.0;
-        if (lon < -180.0) lon += 360.0;
-        return lon;
-    }
-
-    private static double distanceToDegreesLatitude(double distance) {
-        return distance / APPROXIMATE_METERS_PER_DEGREE_AT_EQUATOR;
-    }
-
-    /**
-     * Requires latitude since longitudinal distances change with distance from equator.
-     */
-    private static double distanceToDegreesLongitude(double distance, double lat) {
-        return distance / APPROXIMATE_METERS_PER_DEGREE_AT_EQUATOR / Math.cos(lat);
-    }
-
-    /**
-     * Fudge a location into a coarse location.
-     * <p>Add a random offset, then quantize the result (snap-to-grid).
-     * Random offsets alone can be low-passed pretty easily.
-     * Snap-to-grid on its own is excellent unless you are sitting on a
-     * grid boundary and bouncing between quantizations.
-     * The combination is quite hard to reverse engineer.
-     * <p>The random offset used is smaller than the goal accuracy
-     * ({@link #COARSE_ACCURACY_M}), in order to give relatively stable
-     * results after quantization.
-     */
-    private static Location createCoarse(Location fine) {
-        Location coarse = new Location(fine);
-
-        coarse.removeBearing();
-        coarse.removeSpeed();
-        coarse.removeAltitude();
-
-        double lat = coarse.getLatitude();
-        double lon = coarse.getLongitude();
-
-        // wrap
-        lat = wrapLatitude(lat);
-        lon = wrapLongitude(lon);
-
-        if (coarse.getAccuracy() < COARSE_ACCURACY_M / 2) {
-            // apply a random offset
-            double fudgeDistance = COARSE_ACCURACY_M / 2.0 - coarse.getAccuracy();
-            lat += (Math.random() - 0.5) * distanceToDegreesLatitude(fudgeDistance);
-            lon += (Math.random() - 0.5) * distanceToDegreesLongitude(fudgeDistance, lat);
-        }
-
-        // wrap
-        lat = wrapLatitude(lat);
-        lon = wrapLongitude(lon);
-
-        // quantize (snap-to-grid)
-        double latGranularity = distanceToDegreesLatitude(COARSE_ACCURACY_M);
-        double lonGranularity = distanceToDegreesLongitude(COARSE_ACCURACY_M, lat);
-        long latQuantized = Math.round(lat / latGranularity);
-        long lonQuantized = Math.round(lon / lonGranularity);
-        lat = latQuantized * latGranularity;
-        lon = lonQuantized * lonGranularity;
-
-        // wrap again
-        lat = wrapLatitude(lat);
-        lon = wrapLongitude(lon);
-
-        // apply
-        coarse.setLatitude(lat);
-        coarse.setLongitude(lon);
-        coarse.setAccuracy((float)COARSE_ACCURACY_M);
-
-        return coarse;
-    }
-
-
-    private static Location getCoarseLocationExtra(Location location) {
-        Bundle extras = location.getExtras();
-        if (extras == null) return null;
-        Parcelable parcel = extras.getParcelable(EXTRA_COARSE_LOCATION);
-        if (parcel == null) return null;
-        if (!(parcel instanceof Location)) return null;
-        Location coarse = (Location) parcel;
-        if (coarse.getAccuracy() < COARSE_ACCURACY_M) return null;
-        return coarse;
-    }
-
-    private static Location addCoarseLocationExtra(Location location) {
-        Bundle extras = location.getExtras();
-        if (extras == null) extras = new Bundle();
-        Location coarse = createCoarse(location);
-        extras.putParcelable(EXTRA_COARSE_LOCATION, coarse);
-        location.setExtras(extras);
-        return coarse;
-    }
-
     private void log(String log) {
         if (Log.isLoggable(TAG, Log.VERBOSE)) {
             Slog.d(TAG, log);
@@ -1819,6 +1720,9 @@ protected void dump(FileDescriptor fd, PrintWriter pw, String[] args) {
                 }
             }
 
+            pw.append("  fudger: ");
+            mLocationFudger.dump(fd, pw,  args);
+
             if (args.length > 0 && "short".equals(args[0])) {
                 return;
             }