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Improve Location object.

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Add getElapsedRealtimeNano():

Currently Location just has getTime() and setTime() based on UTC time.
This is entirely unreliable since it is not guaranteed monotonic.
There is a lot of code that compares fix age based on deltas -
and it is all broken in the case of a system clock change. System
clock can change when switching cellular networks (and in some
cases when switching towers).

Document the meaning of getAccuracy():
It is the horizontal, 95% confidence radius.

Make some fields mandatory if they are reported by a LocationProvider:

All Locations returned by a LocationProvider must include at the
minimum a lat, long, timestamps, and accuracy. This is necessary
to perform fused location. There are no public API's for applications
to feed locations into a location provider so this should not cause
any breakage.

If a LocationProvider does not fill in enough fields on a Location
object then it is dropped, and logged.

Bug: 4305998
Change-Id: I7df77125d8a64e174d7bc8c2708661b4f33461ea
This commit is contained in:
Nick Pelly
2012-07-18 13:13:37 -07:00
parent b8acd060d4
commit 2eeeec248a
7 changed files with 137 additions and 14 deletions
Download Patch File Download Diff File Expand all files Collapse all files

107
location/java/android/location/Location.java
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@@ -19,6 +19,7 @@ package android.location;
import android.os.Bundle;
import android.os.Parcel;
import android.os.Parcelable;
import android.os.SystemClock;
import android.util.Printer;
import java.text.DecimalFormat;
@@ -59,6 +60,7 @@ public class Location implements Parcelable {
private String mProvider;
private long mTime = 0;
private long mElapsedRealtimeNano = 0;
private double mLatitude = 0.0;
private double mLongitude = 0.0;
private boolean mHasAltitude = false;
@@ -84,6 +86,7 @@ public class Location implements Parcelable {
public void dump(Printer pw, String prefix) {
pw.println(prefix + "mProvider=" + mProvider + " mTime=" + mTime);
pw.println(prefix + "mElapsedRealtimeNano=" + mElapsedRealtimeNano);
pw.println(prefix + "mLatitude=" + mLatitude + " mLongitude=" + mLongitude);
pw.println(prefix + "mHasAltitude=" + mHasAltitude + " mAltitude=" + mAltitude);
pw.println(prefix + "mHasSpeed=" + mHasSpeed + " mSpeed=" + mSpeed);
@@ -118,6 +121,7 @@ public class Location implements Parcelable {
public void set(Location l) {
mProvider = l.mProvider;
mTime = l.mTime;
mElapsedRealtimeNano = l.mElapsedRealtimeNano;
mLatitude = l.mLatitude;
mLongitude = l.mLongitude;
mHasAltitude = l.mHasAltitude;
@@ -137,6 +141,7 @@ public class Location implements Parcelable {
public void reset() {
mProvider = null;
mTime = 0;
mElapsedRealtimeNano = 0;
mLatitude = 0;
mLongitude = 0;
mHasAltitude = false;
@@ -467,23 +472,62 @@ public class Location implements Parcelable {
}
/**
* Returns the UTC time of this fix, in milliseconds since January 1,
* Return the UTC time of this fix, in milliseconds since January 1,
* 1970.
* <p>Note that the UTC time on a device is not monotonic: it
* can jump forwards or backwards unpredictably. So always use
* {@link #getElapsedRealtimeNano()} when calculating time deltas.
* <p>On the other hand, {@link #getTime()} is useful for presenting
* a human readable time to the user, or for carefully comparing
* location fixes across reboot or across devices.
* <p>This method will always return a valid timestamp on
* Locations generated by a {@link LocationProvider}.
*
* @return time of fix, in milliseconds since January 1, 1970.
*/
public long getTime() {
return mTime;
}
/**
* Sets the UTC time of this fix, in milliseconds since January 1,
* Set the UTC time of this fix, in milliseconds since January 1,
* 1970.
*
* @param time UTC time of this fix, in milliseconds since January 1, 1970
*/
public void setTime(long time) {
mTime = time;
}
/**
* Returns the latitude of this fix.
* Return the time of this fix, in elapsed real-time since system boot.
* <p>This value can be reliably compared to
* {@link android.os.SystemClock#elapsedRealtimeNano()},
* to calculate the age of a fix, and to compare Location fixes, since
* elapsed real-time is guaranteed monotonic for each system boot, and
* continues to increment even when the system is in deep sleep.
* <p>This method will always return a valid timestamp on
* Locations generated by a {@link LocationProvider}.
*
* @return elapsed real-time of fix, in nanoseconds since system boot.
*/
public long getElapsedRealtimeNano() {
return mElapsedRealtimeNano;
}
/**
* Set the time of this fix, in elapsed real-time since system boot.
*
* @param time elapsed real-time of fix, in nanoseconds since system boot.
*/
public void setElapsedRealtimeNano(long time) {
mElapsedRealtimeNano = time;
}
/**
* Return the latitude of this fix.
* <p>This method will always return a valid latitude on
* Locations generated by a {@link LocationProvider}.
*/
public double getLatitude() {
return mLatitude;
@@ -497,7 +541,9 @@ public class Location implements Parcelable {
}
/**
* Returns the longitude of this fix.
* Return the longitude of this fix.
* <p>This method will always return a valid longitude on
* Locations generated by a {@link LocationProvider}.
*/
public double getLongitude() {
return mLongitude;
@@ -619,16 +665,27 @@ public class Location implements Parcelable {
}
/**
* Returns true if the provider is able to report accuracy information,
* false otherwise. The default implementation returns false.
* Return true if this Location has an associated accuracy.
* <p>All Location objects generated by a {@link LocationProvider}
* will have an accuracy.
*/
public boolean hasAccuracy() {
return mHasAccuracy;
}
/**
* Returns the accuracy of the fix in meters. If hasAccuracy() is false,
* 0.0 is returned.
* Return the accuracy of this Location fix.
* <p>Accuracy is measured in meters, and indicates the
* radius of 95% confidence.
* In other words, there is a 95% probability that the
* true location is within a circle centered at the reported
* location, with radius of the reported accuracy.
* <p>This is only a measure of horizontal accuracy, and does
* not indicate the accuracy of bearing, velocity or altitude
* if those are included in this Location.
* <p>If {@link #hasAccuracy} is false, 0.0 is returned.
* <p>All Location object generated by a {@link LocationProvider}
* will have a valid accuracy.
*/
public float getAccuracy() {
return mAccuracy;
@@ -652,6 +709,37 @@ public class Location implements Parcelable {
mHasAccuracy = false;
}
/**
* Return true if this Location object has enough data set to
* be considered a valid fix from a {@link LocationProvider}.
* @see #makeComplete
* @hide
*/
public boolean isComplete() {
if (mProvider == null) return false;
if (!mHasAccuracy) return false;
if (mTime == 0) return false;
if (mElapsedRealtimeNano == 0) return false;
return true;
}
/**
* Helper to fill in incomplete fields.
* Only use this to assist in backwards compatibility
* with Location objects received from applications.
* @see #isComplete
* @hide
*/
public void makeComplete() {
if (mProvider == null) mProvider = "?";
if (!mHasAccuracy) {
mHasAccuracy = true;
mAccuracy = 100.0f;
}
if (mTime == 0) mTime = System.currentTimeMillis();
if (mElapsedRealtimeNano == 0) mElapsedRealtimeNano = SystemClock.elapsedRealtimeNano();
}
/**
* Returns additional provider-specific information about the
* location fix as a Bundle. The keys and values are determined
@@ -681,6 +769,7 @@ public class Location implements Parcelable {
@Override public String toString() {
return "Location[mProvider=" + mProvider +
",mTime=" + mTime +
",mElapsedRealtimeNano=" + mElapsedRealtimeNano +
",mLatitude=" + mLatitude +
",mLongitude=" + mLongitude +
",mHasAltitude=" + mHasAltitude +
@@ -700,6 +789,7 @@ public class Location implements Parcelable {
String provider = in.readString();
Location l = new Location(provider);
l.mTime = in.readLong();
l.mElapsedRealtimeNano = in.readLong();
l.mLatitude = in.readDouble();
l.mLongitude = in.readDouble();
l.mHasAltitude = in.readInt() != 0;
@@ -726,6 +816,7 @@ public class Location implements Parcelable {
public void writeToParcel(Parcel parcel, int flags) {
parcel.writeString(mProvider);
parcel.writeLong(mTime);
parcel.writeLong(mElapsedRealtimeNano);
parcel.writeDouble(mLatitude);
parcel.writeDouble(mLongitude);
parcel.writeInt(mHasAltitude ? 1 : 0);