Improve geofencing: throttle location updates with distance to fence.
Previously any geofence (proximity alert) would turn the GPS on at full rate.
Now, we modify the GPS interval with the distance to the nearest geofence.
A speed of 100m/s is assumed to calculate the next GPS update.
Also
o Major refactor of geofencing code, to make it easier to continue to improve.
o Discard proximity alerts when an app is removed.
o Misc cleanup of nearby code. There are other upcoming changes
that make this a good time for some house-keeping.
TODO:
The new geofencing heuristics are much better than before, but still
relatively naive. The next steps could be:
- Improve boundary detection
- Improve update thottling for large geofences
- Consider velocity when throttling
Change-Id: Ie6e23d2cb2b931eba5d2a2fc759543bb96e2f7d0
diff --git a/services/java/com/android/server/location/Geofence.java b/services/java/com/android/server/location/Geofence.java
new file mode 100644
index 0000000..f63607a
--- /dev/null
+++ b/services/java/com/android/server/location/Geofence.java
@@ -0,0 +1,100 @@
+/*
+ * 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.server.location;
+
+import android.location.Location;
+
+/**
+ * Represents a simple circular GeoFence.
+ */
+public class Geofence {
+ public final static int FLAG_ENTER = 0x01;
+ public final static int FLAG_EXIT = 0x02;
+
+ static final int STATE_UNKNOWN = 0;
+ static final int STATE_INSIDE = 1;
+ static final int STATE_OUTSIDE = 2;
+
+ final double mLatitude;
+ final double mLongitude;
+ final float mRadius;
+ final Location mLocation;
+
+ int mState; // current state
+ double mDistance; // current distance to center of fence
+
+ public Geofence(double latitude, double longitude, float radius, Location prevLocation) {
+ mState = STATE_UNKNOWN;
+
+ mLatitude = latitude;
+ mLongitude = longitude;
+ mRadius = radius;
+
+ mLocation = new Location("");
+ mLocation.setLatitude(latitude);
+ mLocation.setLongitude(longitude);
+
+ if (prevLocation != null) {
+ processLocation(prevLocation);
+ }
+ }
+
+ /**
+ * Process a new location.
+ * @return FLAG_ENTER or FLAG_EXIT if the fence was crossed, 0 otherwise
+ */
+ public int processLocation(Location location) {
+ mDistance = mLocation.distanceTo(location);
+
+ int prevState = mState;
+ //TODO: inside/outside detection could be made more rigorous
+ boolean inside = mDistance <= Math.max(mRadius, location.getAccuracy());
+ if (inside) {
+ mState = STATE_INSIDE;
+ } else {
+ mState = STATE_OUTSIDE;
+ }
+
+ if (prevState != 0 && mState != prevState) {
+ if (mState == STATE_INSIDE) return FLAG_ENTER;
+ if (mState == STATE_OUTSIDE) return FLAG_EXIT;
+ }
+ return 0;
+ }
+
+ public double getDistance() {
+ return mDistance;
+ }
+
+ @Override
+ public String toString() {
+ String state;
+ switch (mState) {
+ case STATE_INSIDE:
+ state = "IN";
+ break;
+ case STATE_OUTSIDE:
+ state = "OUT";
+ break;
+ default:
+ state = "?";
+ }
+ return String.format("(%.4f, %.4f r=%.0f d=%.0f %s)", mLatitude, mLongitude, mRadius,
+ mDistance, state);
+ }
+}