Location overhaul, major commit.

Themes: Fused Location, Geofencing, LocationRequest.

API changes
o Fused location is always returned when asking for location by Criteria.
o Fused location is never returned as a LocationProvider object, nor returned
  as a provider String. This wouldn't make sense because the current API
  design assumes that LocationProvider's have fixed properties (accuracy, power
  etc).
o The fused location engine will tune itself based on the criteria passed
  by applications.
o Deprecate LocationProvider. Apps should use fused location (via Criteria
  class), instead of enumerating through LocationProvider objects. It is
  also over-engineered: designed for a world with a plethora of location
  providers that never materialized.
o The Criteria class is also over-engineered, with many methods that aren't
  currently used, but for now we won't deprecate them since they may have
  value in the future. It is now used to tune the fused location engine.
o Deprecate getBestProvider() and getProvider().
o Add getLastKnownLocation(Criteria), so we can return last known
  fused locations.
o Apps with only ACCESS_COARSE_LOCATION _can_ now use the GPS, but the location
  they receive will be fudged to a 1km radius. They can also use NETWORK
  and fused locatoins, which are fudged in the same way if necessary.
o Totally deprecate Criteria, in favor of LocationRequest.
  Criteria was designed to map QOS to a location provider. What we
  really need is to map QOS to _locations_.
  The death knell was the conflicting ACCURACY_ constants on
  Criteria, with values 1, 2, 3, 1, 2. Yes not a typo.
o Totally deprecate LocationProvider.
o Deprecate test/mock provider support. They require a named provider,
  which is a concept we are moving away from. We do not yet have a
  replacement, but I think its ok to deprecate since you also
  need to have 'allow mock locations' checked in developer settings.
  They will continue to work.
o Deprecate event codes associated with provider status. The fused
  provider is _always_ available.
o Introduce Geofence data object to provide an easier path fowards
  for polygons etc.

Implementation changes
o Fused implementation: incoming (GPS and NLP) location fixes are given
  a weight, that exponentially decays with respect to age and accuracy.
  The half-life of age is ~60 seconds, and the half-life of accuracy is
  ~20 meters. The fixes are weighted and combined to output a fused
  location.
o Move Fused Location impl into
  frameworks/base/packages/FusedLocation
o Refactor Fused Location behind the IProvider AIDL interface. This allow us
  to distribute newer versions of Fused Location in a new APK, at run-time.
o Introduce ServiceWatcher.java, to refactor code used for run-time upgrades of
  Fused Location, and the NLP.
o Fused Location is by default run in the system server (but can be moved to
  any process or pacakge, even at run-time).
o Plumb the Criteria requirements through to the Fused Location provider via
  ILocation.sendExtraCommand(). I re-used this interface to avoid modifying the
  ILocation interface, which would have broken run-time upgradability of the
  NLP.
o Switch the geofence manager to using fused location.
o Clean up 'adb shell dumpsys location' output.
o Introduce config_locationProviderPackageNames and
  config_overlay_locationProviderPackageNames to configure the default
  and overlay package names for Geocoder, NLP and FLP.
o Lots of misc cleanup.
o Improve location fudging. Apply random vector then quantize.
o Hide internal POJO's from clients of com.android.location.provider.jar
  (NLP and FLP). Introduce wrappers ProviderRequestUnbundled and
  ProviderPropertiesUnbundled.
o Introduce ProviderProperties to collapse all the provider accuracy/
  bearing/altitude/power plumbing (that is deprecated anyway).
o DELETE lots of code: DummyLocationProvider,
o Rename the (internal) LocationProvider to LocationProviderBase.
o Plumb pid, uid and packageName throughout
  LocationManagerService#Receiver to support future features.

TODO: The FLP and Geofencer have a lot of room to be more intelligent
TODO: Documentation
TODO: test test test

Change-Id: Iacefd2f176ed40ce1e23b090a164792aa8819c55

8 files changed, 790 insertions, 0 deletions

diff --git a/packages/FusedLocation/Android.mk b/packages/FusedLocation/Android.mk
new file mode 100644
index 0000000..318782f
--- /dev/null
+++ b/packages/FusedLocation/Android.mk
@@ -0,0 +1,27 @@
+# Copyright (C) 2012 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+LOCAL_PATH:= $(call my-dir)
+include $(CLEAR_VARS)
+
+LOCAL_MODULE_TAGS := optional
+
+LOCAL_SRC_FILES := $(call all-subdir-java-files)
+
+LOCAL_JAVA_LIBRARIES := com.android.location.provider
+
+LOCAL_PACKAGE_NAME := FusedLocation
+LOCAL_CERTIFICATE := platform
+
+include $(BUILD_PACKAGE)
diff --git a/packages/FusedLocation/AndroidManifest.xml b/packages/FusedLocation/AndroidManifest.xml
new file mode 100644
index 0000000..4c57401
--- /dev/null
+++ b/packages/FusedLocation/AndroidManifest.xml
@@ -0,0 +1,45 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!--
+/*
+ * Copyright (c) 2012 Google Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+-->
+<manifest xmlns:android="http://schemas.android.com/apk/res/android"
+        package="com.android.location.fused"
+        coreApp="true">
+
+    <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
+    <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
+    <uses-permission android:name="android.permission.INSTALL_LOCATION_PROVIDER" />
+
+    <application
+            android:label="@string/app_label"
+            android:process="system">
+
+        <uses-library android:name="com.android.location.provider" />
+
+        <!-- Fused Location Service that LocationManagerService binds to.
+             LocationManagerService will bind to the service with the highest
+             version. -->
+        <service android:name="com.android.location.fused.FusedLocationService"
+                 android:exported="true"
+                 android:permission="android.permission.WRITE_SECURE_SETTINGS" >
+           <intent-filter>
+               <action android:name="com.android.location.service.FusedLocationProvider" />
+           </intent-filter>
+           <meta-data android:name="version" android:value="1" />
+        </service>
+    </application>
+</manifest>
diff --git a/packages/FusedLocation/MODULE_LICENSE_APACHE2 b/packages/FusedLocation/MODULE_LICENSE_APACHE2
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/packages/FusedLocation/MODULE_LICENSE_APACHE2
diff --git a/packages/FusedLocation/NOTICE b/packages/FusedLocation/NOTICE
new file mode 100644
index 0000000..33ff961
--- /dev/null
+++ b/packages/FusedLocation/NOTICE
@@ -0,0 +1,190 @@
+
+   Copyright (c) 2005-2012, The Android Open Source Project
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+
+
+                                 Apache License
+                           Version 2.0, January 2004
+                        http://www.apache.org/licenses/
+
+   TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
+
+   1. Definitions.
+
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+      outstanding shares, or (iii) beneficial ownership of such entity.
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+      editorial revisions, annotations, elaborations, or other modifications
+      represent, as a whole, an original work of authorship. For the purposes
+      of this License, Derivative Works shall not include works that remain
+      separable from, or merely link (or bind by name) to the interfaces of,
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+      "Contribution" shall mean any work of authorship, including
+      the original version of the Work and any modifications or additions
+      to that Work or Derivative Works thereof, that is intentionally
+      submitted to Licensor for inclusion in the Work by the copyright owner
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+      to the Licensor or its representatives, including but not limited to
+      communication on electronic mailing lists, source code control systems,
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+      "Contributor" shall mean Licensor and any individual or Legal Entity
+      on behalf of whom a Contribution has been received by Licensor and
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+   2. Grant of Copyright License. Subject to the terms and conditions of
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+      (except as stated in this section) patent license to make, have made,
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+      by such Contributor that are necessarily infringed by their
+      Contribution(s) alone or by combination of their Contribution(s)
+      with the Work to which such Contribution(s) was submitted. If You
+      institute patent litigation against any entity (including a
+      cross-claim or counterclaim in a lawsuit) alleging that the Work
+      or a Contribution incorporated within the Work constitutes direct
+      or contributory patent infringement, then any patent licenses
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+   4. Redistribution. You may reproduce and distribute copies of the
+      Work or Derivative Works thereof in any medium, with or without
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+      meet the following conditions:
+
+      (a) You must give any other recipients of the Work or
+          Derivative Works a copy of this License; and
+
+      (b) You must cause any modified files to carry prominent notices
+          stating that You changed the files; and
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+      (c) You must retain, in the Source form of any Derivative Works
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+      the conditions stated in this License.
+
+   5. Submission of Contributions. Unless You explicitly state otherwise,
+      any Contribution intentionally submitted for inclusion in the Work
+      by You to the Licensor shall be under the terms and conditions of
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+      Notwithstanding the above, nothing herein shall supersede or modify
+      the terms of any separate license agreement you may have executed
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+   6. Trademarks. This License does not grant permission to use the trade
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+   7. Disclaimer of Warranty. Unless required by applicable law or
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+      Contributor provides its Contributions) on an "AS IS" BASIS,
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+      whether in tort (including negligence), contract, or otherwise,
+      unless required by applicable law (such as deliberate and grossly
+      negligent acts) or agreed to in writing, shall any Contributor be
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+   END OF TERMS AND CONDITIONS
+
diff --git a/packages/FusedLocation/res/values/strings.xml b/packages/FusedLocation/res/values/strings.xml
new file mode 100644
index 0000000..5b78e39
--- /dev/null
+++ b/packages/FusedLocation/res/values/strings.xml
@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+    <!-- Name of the application. [CHAR LIMIT=35] -->
+    <string name="app_label">Fused Location</string>
+</resources>
diff --git a/packages/FusedLocation/src/com/android/location/fused/FusedLocationProvider.java b/packages/FusedLocation/src/com/android/location/fused/FusedLocationProvider.java
new file mode 100644
index 0000000..45f05f3
--- /dev/null
+++ b/packages/FusedLocation/src/com/android/location/fused/FusedLocationProvider.java
@@ -0,0 +1,118 @@
+/*
+ * Copyright (C) 2012 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.location.fused;
+
+
+import java.io.FileDescriptor;
+import java.io.PrintWriter;
+
+import com.android.location.provider.LocationProviderBase;
+import com.android.location.provider.ProviderPropertiesUnbundled;
+import com.android.location.provider.ProviderRequestUnbundled;
+
+import android.content.Context;
+import android.location.Criteria;
+import android.location.LocationProvider;
+import android.os.Bundle;
+import android.os.Handler;
+import android.os.Looper;
+import android.os.Message;
+import android.os.WorkSource;
+
+public class FusedLocationProvider extends LocationProviderBase implements FusionEngine.Callback {
+    private static final String TAG = "FusedLocationProvider";
+
+    private static ProviderPropertiesUnbundled PROPERTIES = ProviderPropertiesUnbundled.create(
+            false, false, false, false, true, true, true, Criteria.POWER_LOW,
+            Criteria.ACCURACY_FINE);
+
+    private static final int MSG_ENABLE = 1;
+    private static final int MSG_DISABLE = 2;
+    private static final int MSG_SET_REQUEST = 3;
+
+    private final Context mContext;
+    private final FusionEngine mEngine;
+
+    private static class RequestWrapper {
+        public ProviderRequestUnbundled request;
+        public WorkSource source;
+        public RequestWrapper(ProviderRequestUnbundled request, WorkSource source) {
+            this.request = request;
+            this.source = source;
+        }
+    }
+
+    public FusedLocationProvider(Context context) {
+        super(TAG, PROPERTIES);
+        mContext = context;
+        mEngine = new FusionEngine(context, Looper.myLooper());
+    }
+
+    /**
+     * For serializing requests to mEngine.
+     */
+    private Handler mHandler = new Handler() {
+        @Override
+        public void handleMessage(Message msg) {
+            switch (msg.what) {
+                case MSG_ENABLE:
+                    mEngine.init(FusedLocationProvider.this);
+                    break;
+                case MSG_DISABLE:
+                    mEngine.deinit();
+                    break;
+                case MSG_SET_REQUEST:
+                    {
+                        RequestWrapper wrapper = (RequestWrapper) msg.obj;
+                        mEngine.setRequirements(wrapper.request, wrapper.source);
+                        break;
+                    }
+            }
+        }
+    };
+
+    @Override
+    public void onEnable() {
+        mHandler.sendEmptyMessage(MSG_ENABLE);
+    }
+
+    @Override
+    public void onDisable() {
+        mHandler.sendEmptyMessage(MSG_DISABLE);
+    }
+
+    @Override
+    public void onSetRequest(ProviderRequestUnbundled request, WorkSource source) {
+        mHandler.obtainMessage(MSG_SET_REQUEST,  new RequestWrapper(request, source));
+    }
+
+    @Override
+    public void onDump(FileDescriptor fd, PrintWriter pw, String[] args) {
+        // perform synchronously
+        mEngine.dump(fd, pw, args);
+    }
+
+    @Override
+    public int onGetStatus(Bundle extras) {
+        return LocationProvider.AVAILABLE;
+    }
+
+    @Override
+    public long onGetStatusUpdateTime() {
+        return 0;
+    }
+}
diff --git a/packages/FusedLocation/src/com/android/location/fused/FusedLocationService.java b/packages/FusedLocation/src/com/android/location/fused/FusedLocationService.java
new file mode 100644
index 0000000..509c010
--- /dev/null
+++ b/packages/FusedLocation/src/com/android/location/fused/FusedLocationService.java
@@ -0,0 +1,50 @@
+/*
+ * Copyright (C) 2012 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.location.fused;
+
+import java.io.FileDescriptor;
+import java.io.PrintWriter;
+
+import android.app.Service;
+import android.content.Intent;
+import android.os.IBinder;
+
+public class FusedLocationService extends Service {
+    private FusedLocationProvider mProvider;
+
+    @Override
+    public IBinder onBind(Intent intent) {
+        if (mProvider == null) {
+            mProvider = new FusedLocationProvider(getApplicationContext());
+        }
+        return mProvider.getBinder();
+    }
+
+    @Override
+    public boolean onUnbind(Intent intent) {
+        // make sure to stop performing work
+        if (mProvider != null) {
+            mProvider.onDisable();
+        }
+      return false;
+    }
+
+    @Override
+    public void onDestroy() {
+        mProvider = null;
+    }
+}
diff --git a/packages/FusedLocation/src/com/android/location/fused/FusionEngine.java b/packages/FusedLocation/src/com/android/location/fused/FusionEngine.java
new file mode 100644
index 0000000..f4f87a8
--- /dev/null
+++ b/packages/FusedLocation/src/com/android/location/fused/FusionEngine.java
@@ -0,0 +1,355 @@
+/*
+ * Copyright (C) 2012 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.location.fused;
+
+import java.io.FileDescriptor;
+import java.io.PrintWriter;
+import java.util.HashMap;
+
+import com.android.location.provider.ProviderRequestUnbundled;
+
+
+import android.content.Context;
+import android.location.Location;
+import android.location.LocationListener;
+import android.location.LocationManager;
+import android.location.LocationRequest;
+import android.os.Bundle;
+import android.os.Looper;
+import android.os.SystemClock;
+import android.os.WorkSource;
+import android.util.Log;
+
+public class FusionEngine implements LocationListener {
+    public interface Callback {
+        public void reportLocation(Location location);
+    }
+
+    private static final String TAG = "FusedLocation";
+    private static final String NETWORK = LocationManager.NETWORK_PROVIDER;
+    private static final String GPS = LocationManager.GPS_PROVIDER;
+
+    // threshold below which a location is considered stale enough
+    // that we shouldn't use its bearing, altitude, speed etc
+    private static final double WEIGHT_THRESHOLD = 0.5;
+    // accuracy in meters at which a Location's weight is halved (compared to 0 accuracy)
+    private static final double ACCURACY_HALFLIFE_M = 20.0;
+    // age in seconds at which a Location's weight is halved (compared to 0 age)
+    private static final double AGE_HALFLIFE_S = 60.0;
+
+    private static final double ACCURACY_DECAY_CONSTANT_M = Math.log(2) / ACCURACY_HALFLIFE_M;
+    private static final double AGE_DECAY_CONSTANT_S = Math.log(2) / AGE_HALFLIFE_S;
+
+    private final Context mContext;
+    private final LocationManager mLocationManager;
+    private final Looper mLooper;
+
+    // all fields are only used on mLooper thread. except for in dump() which is not thread-safe
+    private Callback mCallback;
+    private Location mFusedLocation;
+    private Location mGpsLocation;
+    private Location mNetworkLocation;
+    private double mNetworkWeight;
+    private double mGpsWeight;
+
+    private boolean mEnabled;
+    private ProviderRequestUnbundled mRequest;
+
+    private final HashMap<String, ProviderStats> mStats = new HashMap<String, ProviderStats>();
+
+    public FusionEngine(Context context, Looper looper) {
+        mContext = context;
+        mLocationManager = (LocationManager) context.getSystemService(Context.LOCATION_SERVICE);
+        mNetworkLocation = new Location("");
+        mNetworkLocation.setAccuracy(Float.MAX_VALUE);
+        mGpsLocation = new Location("");
+        mGpsLocation.setAccuracy(Float.MAX_VALUE);
+        mLooper = looper;
+
+        mStats.put(GPS, new ProviderStats());
+        mStats.get(GPS).available = mLocationManager.isProviderEnabled(GPS);
+        mStats.put(NETWORK, new ProviderStats());
+        mStats.get(NETWORK).available = mLocationManager.isProviderEnabled(NETWORK);
+    }
+
+    public void init(Callback callback) {
+        Log.i(TAG, "engine started (" + mContext.getPackageName() + ")");
+        mCallback = callback;
+    }
+
+    /**
+     * Called to stop doing any work, and release all resources
+     * This can happen when a better fusion engine is installed
+     * in a different package, and this one is no longer needed.
+     * Called on mLooper thread
+     */
+    public void deinit() {
+        mRequest = null;
+        disable();
+        Log.i(TAG, "engine stopped (" + mContext.getPackageName() + ")");
+    }
+
+    private boolean isAvailable() {
+        return mStats.get(GPS).available || mStats.get(NETWORK).available;
+    }
+
+    /** Called on mLooper thread */
+    public void enable() {
+        mEnabled = true;
+        updateRequirements();
+    }
+
+    /** Called on mLooper thread */
+    public void disable() {
+        mEnabled = false;
+        updateRequirements();
+    }
+
+    /** Called on mLooper thread */
+    public void setRequirements(ProviderRequestUnbundled request, WorkSource source) {
+        mRequest = request;
+        mEnabled = true;
+        updateRequirements();
+    }
+
+    private static class ProviderStats {
+        public boolean available;
+        public boolean requested;
+        public long requestTime;
+        public long minTime;
+        public long lastRequestTtff;
+        @Override
+        public String toString() {
+            StringBuilder s = new StringBuilder();
+            s.append(available ? "AVAILABLE" : "UNAVAILABLE");
+            s.append(requested ? " REQUESTED" : " ---");
+            return s.toString();
+        }
+    }
+
+    private void enableProvider(String name, long minTime) {
+        ProviderStats stats = mStats.get(name);
+
+        if (!stats.requested) {
+            stats.requestTime = SystemClock.elapsedRealtime();
+            stats.requested = true;
+            stats.minTime = minTime;
+            mLocationManager.requestLocationUpdates(name, minTime, 0, this, mLooper);
+        } else if (stats.minTime != minTime) {
+            stats.minTime = minTime;
+            mLocationManager.requestLocationUpdates(name, minTime, 0, this, mLooper);
+        }
+    }
+
+    private void disableProvider(String name) {
+        ProviderStats stats = mStats.get(name);
+
+        if (stats.requested) {
+            stats.requested = false;
+            mLocationManager.removeUpdates(this);  //TODO GLOBAL
+        }
+    }
+
+    private void updateRequirements() {
+        if (mEnabled == false || mRequest == null) {
+            mRequest = null;
+            disableProvider(NETWORK);
+            disableProvider(GPS);
+            return;
+        }
+
+        ProviderStats gpsStats = mStats.get(GPS);
+        ProviderStats networkStats = mStats.get(NETWORK);
+
+        long networkInterval = Long.MAX_VALUE;
+        long gpsInterval = Long.MAX_VALUE;
+        for (LocationRequest request : mRequest.getLocationRequests()) {
+            switch (request.getQuality()) {
+                case LocationRequest.ACCURACY_FINE:
+                case LocationRequest.POWER_HIGH:
+                    if (request.getInterval() < gpsInterval) {
+                        gpsInterval = request.getInterval();
+                    }
+                    if (request.getInterval() < networkInterval) {
+                        networkInterval = request.getInterval();
+                    }
+                    break;
+                case LocationRequest.ACCURACY_BLOCK:
+                case LocationRequest.ACCURACY_CITY:
+                case LocationRequest.POWER_LOW:
+                    if (request.getInterval() < networkInterval) {
+                        networkInterval = request.getInterval();
+                    }
+                    break;
+            }
+        }
+
+        if (gpsInterval < Long.MAX_VALUE) {
+            enableProvider(GPS, gpsInterval);
+        } else {
+            disableProvider(GPS);
+        }
+        if (networkInterval < Long.MAX_VALUE) {
+            enableProvider(NETWORK, networkInterval);
+        } else {
+            disableProvider(NETWORK);
+        }
+    }
+
+    private static double weighAccuracy(Location loc) {
+        double accuracy = loc.getAccuracy();
+        return Math.exp(-accuracy * ACCURACY_DECAY_CONSTANT_M);
+    }
+
+    private static double weighAge(Location loc) {
+        long ageSeconds = SystemClock.elapsedRealtimeNano() - loc.getElapsedRealtimeNano();
+        ageSeconds /= 1000000000L;
+        if (ageSeconds < 0) ageSeconds = 0;
+        return Math.exp(-ageSeconds * AGE_DECAY_CONSTANT_S);
+    }
+
+    private double weigh(double gps, double network) {
+        return (gps * mGpsWeight) + (network * mNetworkWeight);
+    }
+
+    private double weigh(double gps, double network, double wrapMin, double wrapMax) {
+        // apply aliasing
+        double wrapWidth = wrapMax - wrapMin;
+        if (gps - network > wrapWidth / 2) network += wrapWidth;
+        else if (network - gps > wrapWidth / 2) gps += wrapWidth;
+
+        double result = weigh(gps, network);
+
+        // remove aliasing
+        if (result > wrapMax) result -= wrapWidth;
+        return result;
+    }
+
+    private void updateFusedLocation() {
+        // naive fusion
+        mNetworkWeight = weighAccuracy(mNetworkLocation) * weighAge(mNetworkLocation);
+        mGpsWeight = weighAccuracy(mGpsLocation) * weighAge(mGpsLocation);
+        // scale mNetworkWeight and mGpsWeight so that they add to 1
+        double totalWeight = mNetworkWeight + mGpsWeight;
+        mNetworkWeight /= totalWeight;
+        mGpsWeight /= totalWeight;
+
+        Location fused = new Location(LocationManager.FUSED_PROVIDER);
+        // fuse lat/long
+        // assumes the two locations are close enough that earth curvature doesn't matter
+        fused.setLatitude(weigh(mGpsLocation.getLatitude(), mNetworkLocation.getLatitude()));
+        fused.setLongitude(weigh(mGpsLocation.getLongitude(), mNetworkLocation.getLongitude(),
+                -180.0, 180.0));
+
+        // fused accuracy
+        //TODO: use some real math instead of this crude fusion
+        // one suggestion is to fuse in a quadratic manner, eg
+        // sqrt(weigh(gpsAcc^2, netAcc^2)).
+        // another direction to explore is to consider the difference in the 2
+        // locations. If the component locations overlap, the fused accuracy is
+        // better than the component accuracies. If they are far apart,
+        // the fused accuracy is much worse.
+        fused.setAccuracy((float)weigh(mGpsLocation.getAccuracy(), mNetworkLocation.getAccuracy()));
+
+        // fused time - now
+        fused.setTime(System.currentTimeMillis());
+        fused.setElapsedRealtimeNano(SystemClock.elapsedRealtimeNano());
+
+        // fuse altitude
+        if (mGpsLocation.hasAltitude() && !mNetworkLocation.hasAltitude() &&
+                mGpsWeight > WEIGHT_THRESHOLD) {
+            fused.setAltitude(mGpsLocation.getAltitude());   // use GPS
+        } else if (!mGpsLocation.hasAltitude() && mNetworkLocation.hasAltitude() &&
+                mNetworkWeight > WEIGHT_THRESHOLD) {
+            fused.setAltitude(mNetworkLocation.getAltitude());   // use Network
+        } else if (mGpsLocation.hasAltitude() && mNetworkLocation.hasAltitude()) {
+            fused.setAltitude(weigh(mGpsLocation.getAltitude(), mNetworkLocation.getAltitude()));
+        }
+
+        // fuse speed
+        if (mGpsLocation.hasSpeed() && !mNetworkLocation.hasSpeed() &&
+                mGpsWeight > WEIGHT_THRESHOLD) {
+            fused.setSpeed(mGpsLocation.getSpeed());   // use GPS if its not too old
+        } else if (!mGpsLocation.hasSpeed() && mNetworkLocation.hasSpeed() &&
+                mNetworkWeight > WEIGHT_THRESHOLD) {
+            fused.setSpeed(mNetworkLocation.getSpeed());   // use Network
+        } else if (mGpsLocation.hasSpeed() && mNetworkLocation.hasSpeed()) {
+            fused.setSpeed((float)weigh(mGpsLocation.getSpeed(), mNetworkLocation.getSpeed()));
+        }
+
+        // fuse bearing
+        if (mGpsLocation.hasBearing() && !mNetworkLocation.hasBearing() &&
+                mGpsWeight > WEIGHT_THRESHOLD) {
+            fused.setBearing(mGpsLocation.getBearing());   // use GPS if its not too old
+        } else if (!mGpsLocation.hasBearing() && mNetworkLocation.hasBearing() &&
+                mNetworkWeight > WEIGHT_THRESHOLD) {
+            fused.setBearing(mNetworkLocation.getBearing());   // use Network
+        } else if (mGpsLocation.hasBearing() && mNetworkLocation.hasBearing()) {
+            fused.setBearing((float)weigh(mGpsLocation.getBearing(), mNetworkLocation.getBearing(),
+                    0.0, 360.0));
+        }
+
+        mFusedLocation = fused;
+
+        mCallback.reportLocation(mFusedLocation);
+    }
+
+    /** Called on mLooper thread */
+    @Override
+    public void onLocationChanged(Location location) {
+        if (GPS.equals(location.getProvider())) {
+            mGpsLocation = location;
+            updateFusedLocation();
+        } else if (NETWORK.equals(location.getProvider())) {
+            mNetworkLocation = location;
+            updateFusedLocation();
+        }
+    }
+
+    /** Called on mLooper thread */
+    @Override
+    public void onStatusChanged(String provider, int status, Bundle extras) {  }
+
+    /** Called on mLooper thread */
+    @Override
+    public void onProviderEnabled(String provider) {
+        ProviderStats stats = mStats.get(provider);
+        if (stats == null) return;
+
+        stats.available = true;
+    }
+
+    /** Called on mLooper thread */
+    @Override
+    public void onProviderDisabled(String provider) {
+        ProviderStats stats = mStats.get(provider);
+        if (stats == null) return;
+
+        stats.available = false;
+    }
+
+    public void dump(FileDescriptor fd, PrintWriter pw, String[] args) {
+        StringBuilder s = new StringBuilder();
+        s.append("mEnabled=" + mEnabled).append(' ').append(mRequest).append('\n');
+        s.append("fused=").append(mFusedLocation).append('\n');
+        s.append(String.format("gps %.3f %s\n", mGpsWeight, mGpsLocation));
+        s.append("    ").append(mStats.get(GPS)).append('\n');
+        s.append(String.format("net %.3f %s\n", mNetworkWeight, mNetworkLocation));
+        s.append("    ").append(mStats.get(NETWORK)).append('\n');
+        pw.append(s);
+    }
+}