Merge "BugFix: Density-based coarsening: Set the accuracy to the approximate... (a8f92609) · Commits · e / os / android_frameworks_base

services/core/java/com/android/server/location/fudger/LocationFudger.java

+27 −1

Original line number	Original line	Diff line number	Diff line
	@@ -68,6 +68,17 @@ public class LocationFudger {
	private static final double MAX_LATITUDE =		private static final double MAX_LATITUDE =
	90.0 - (1.0 / APPROXIMATE_METERS_PER_DEGREE_AT_EQUATOR);		90.0 - (1.0 / APPROXIMATE_METERS_PER_DEGREE_AT_EQUATOR);

			// The average edge length in km of an S2 cell, indexed by S2 levels 0 to
			// 13. Level 13 is the highest level used for coarsening.
			// This approximation assumes the S2 cells are squares.
			// For density-based coarsening, we use the edge to set the accuracy of the
			// coarsened location.
			// The values are from http://s2geometry.io/resources/s2cell_statistics.html
			// We take square root of the average area.
			private static final float[] S2_CELL_AVG_EDGE_PER_LEVEL = new float[] {
			9220.14f, 4610.07f, 2305.04f, 1152.52f, 576.26f, 288.13f, 144.06f,
			72.03f, 36.02f, 20.79f, 9f, 5.05f, 2.25f, 1.13f, 0.57f};

	private final float mAccuracyM;		private final float mAccuracyM;
	private final Clock mClock;		private final Clock mClock;
	private final Random mRandom;		private final Random mRandom;
	@@ -194,12 +205,14 @@ public class LocationFudger {
	// The new algorithm is applied if and only if (1) the flag is on, (2) the cache has been		// The new algorithm is applied if and only if (1) the flag is on, (2) the cache has been
	// set, and (3) the cache has successfully queried the provider for the default coarsening		// set, and (3) the cache has successfully queried the provider for the default coarsening
	// value.		// value.
			float accuracy = mAccuracyM;
	if (Flags.populationDensityProvider() && Flags.densityBasedCoarseLocations()		if (Flags.populationDensityProvider() && Flags.densityBasedCoarseLocations()
	&& cacheCopy != null) {		&& cacheCopy != null) {
	if (cacheCopy.hasDefaultValue()) {		if (cacheCopy.hasDefaultValue()) {
	// New algorithm that snaps to the center of a S2 cell.		// New algorithm that snaps to the center of a S2 cell.
	int level = cacheCopy.getCoarseningLevel(latitude, longitude);		int level = cacheCopy.getCoarseningLevel(latitude, longitude);
	coarsened = snapToCenterOfS2Cell(latitude, longitude, level);		coarsened = snapToCenterOfS2Cell(latitude, longitude, level);
			accuracy = getS2CellApproximateEdge(level);
	} else {		} else {
	// Try to fetch the default value. The answer won't come in time, but will be used		// Try to fetch the default value. The answer won't come in time, but will be used
	// for the next location to coarsen.		// for the next location to coarsen.
	@@ -214,7 +227,7 @@ public class LocationFudger {

	coarse.setLatitude(coarsened[LAT_INDEX]);		coarse.setLatitude(coarsened[LAT_INDEX]);
	coarse.setLongitude(coarsened[LNG_INDEX]);		coarse.setLongitude(coarsened[LNG_INDEX]);
	coarse.setAccuracy(Math.max(mAccuracyM, coarse.getAccuracy()));		coarse.setAccuracy(Math.max(accuracy, coarse.getAccuracy()));

	synchronized (this) {		synchronized (this) {
	mCachedFineLocation = fine;		mCachedFineLocation = fine;
	@@ -224,6 +237,19 @@ public class LocationFudger {
	return coarse;		return coarse;
	}		}

			// Returns the average edge length in meters of an S2 cell at the given
			// level. This is computed as if the S2 cell were a square. We do not need
			// an exact value, only a rough approximation.
			@VisibleForTesting
			protected float getS2CellApproximateEdge(int level) {
			if (level < 0) {
			level = 0;
			} else if (level >= S2_CELL_AVG_EDGE_PER_LEVEL.length) {
			level = S2_CELL_AVG_EDGE_PER_LEVEL.length - 1;
			}
			return S2_CELL_AVG_EDGE_PER_LEVEL[level] * 1000;
			}

	// quantize location by snapping to a grid. this is the primary means of obfuscation. it		// quantize location by snapping to a grid. this is the primary means of obfuscation. it
	// gives nice consistent results and is very effective at hiding the true location (as		// gives nice consistent results and is very effective at hiding the true location (as
	// long as you are not sitting on a grid boundary, which the random offsets mitigate).		// long as you are not sitting on a grid boundary, which the random offsets mitigate).

services/tests/mockingservicestests/src/com/android/server/location/fudger/LocationFudgerTest.java

+27 −0

Original line number	Original line	Diff line number	Diff line
	@@ -271,4 +271,31 @@ public class LocationFudgerTest {
	assertThat(center[0]).isEqualTo(expected[0]);		assertThat(center[0]).isEqualTo(expected[0]);
	assertThat(center[1]).isEqualTo(expected[1]);		assertThat(center[1]).isEqualTo(expected[1]);
	}		}

			@Test
			public void getS2CellApproximateEdge_returnsCorrectRadius() {
			int level = 10;

			float radius = mFudger.getS2CellApproximateEdge(level);

			assertThat(radius).isEqualTo(9000); // in meters
			}

			@Test
			public void getS2CellApproximateEdge_doesNotThrow() {
			int level = -1;

			mFudger.getS2CellApproximateEdge(level);

			// No exception thrown.
			}

			@Test
			public void getS2CellApproximateEdge_doesNotThrow2() {
			int level = 14;

			mFudger.getS2CellApproximateEdge(level);

			// No exception thrown.
			}
	}		}