Fix issue #1574: Add location accuracy filter to prevent GPS drift

Author: Ahmed-Makled

geolocator_android/CHANGELOG.md

@@ -1,3 +1,11 @@
+## UNRELEASED
+
+* Adds location accuracy filtering to prevent random GPS drifts (Issue #1574). Features added:
+  * `LocationAccuracyFilter` class to filter out location updates with unrealistic movement patterns
+  * Optional filtering through new `enableAccuracyFilter` parameter
+  * Configurable thresholds for accuracy, speed, and distance jumps
+  * Comprehensive test coverage for various transportation modes
+
 ## 5.0.1+1
 
 - Bump `androidx.core:core` to version 1.16.0

geolocator_android/android/src/main/java/com/baseflow/geolocator/location/FusedLocationClient.java

@@ -79,7 +79,11 @@ public synchronized void onLocationResult(@NonNull LocationResult locationResult
             }
 
             nmeaClient.enrichExtrasWithNmea(location);
-            positionChangedCallback.onPositionChanged(location);
+            
+            // Apply the location accuracy filter before reporting the position
+            if (LocationAccuracyFilter.shouldAcceptLocation(location)) {
+              positionChangedCallback.onPositionChanged(location);
+            }
           }
 
           @Override
@@ -230,6 +234,13 @@ public void startPositionUpdates(
     this.positionChangedCallback = positionChangedCallback;
     this.errorCallback = errorCallback;
 
+    // Enable or disable the location accuracy filter based on options
+    if (this.locationOptions != null) {
+      LocationAccuracyFilter.setFilterEnabled(this.locationOptions.isEnableAccuracyFilter());
+    } else {
+      LocationAccuracyFilter.setFilterEnabled(false);
+    }
+
     LocationRequest locationRequest = buildLocationRequest(this.locationOptions);
     LocationSettingsRequest settingsRequest = buildLocationSettingsRequest(locationRequest);
 
@@ -278,5 +289,7 @@ public void startPositionUpdates(
   public void stopPositionUpdates() {
     this.nmeaClient.stop();
     fusedLocationProviderClient.removeLocationUpdates(locationCallback);
+    // Reset the location filter when updates are stopped
+    LocationAccuracyFilter.reset();
   }
 }

geolocator_android/android/src/main/java/com/baseflow/geolocator/location/LocationAccuracyFilter.java

@@ -0,0 +1,112 @@
+package com.baseflow.geolocator.location;
+
+import android.location.Location;
+import android.util.Log;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+
+/**
+ * Utility class to filter inaccurate location updates that might cause GPS drift.
+ * Detects and filters out positions that are physically implausible based on
+ * speed, distance, and accuracy.
+ */
+public class LocationAccuracyFilter {
+    private static final String TAG = "LocationAccuracyFilter";
+
+    // Constants for filtering
+    private static final float MAX_ACCURACY_THRESHOLD = 300.0f; // meters
+    private static final float MAX_SPEED_THRESHOLD = 280.0f; // m/s (~1000 km/h to support aircraft)
+    private static final float MAX_DISTANCE_JUMP = 1000.0f; // meters
+
+    @Nullable private static Location lastFilteredLocation = null;
+    private static boolean filterEnabled = false;
+
+    /**
+     * Sets whether filtering is enabled.
+     * This should be called when starting location updates based on user preferences.
+     *
+     * @param enabled Whether filtering should be enabled
+     */
+    public static void setFilterEnabled(boolean enabled) {
+        filterEnabled = enabled;
+        // Reset the filter state when changing the setting
+        if (enabled) {
+            reset();
+        }
+    }
+
+    /**
+     * Checks if a location update should be accepted based on realistic movement patterns.
+     *
+     * @param newLocation The new location to evaluate
+     * @return true if the location should be accepted, false if it should be filtered
+     */
+    public static boolean shouldAcceptLocation(@NonNull Location newLocation) {
+        // If filtering is disabled, always accept locations
+        if (!filterEnabled) {
+            return true;
+        }
+
+        // Always accept the first position
+        if (lastFilteredLocation == null) {
+            lastFilteredLocation = newLocation;
+            return true;
+        }
+
+        // Time difference in seconds
+        float timeDelta = (newLocation.getTime() - lastFilteredLocation.getTime()) / 1000.0f;
+
+        // Don't filter if time hasn't advanced
+        if (timeDelta <= 0) {
+            lastFilteredLocation = newLocation;
+            return true;
+        }
+
+        // Calculate distance in meters
+        float distance = newLocation.distanceTo(lastFilteredLocation);
+
+        // Calculate speed (m/s)
+        float speed = distance / timeDelta;
+
+        // Get position accuracy (if available)
+        float accuracy = newLocation.hasAccuracy() ? newLocation.getAccuracy() : 0.0f;
+
+        // Filters to apply - use a conservative approach to avoid affecting legitimate use cases
+        boolean shouldFilter = false;
+
+        // Filter based on very poor accuracy - this catches points with extremely poor accuracy
+        if (accuracy > MAX_ACCURACY_THRESHOLD) {
+            Log.d(TAG, "Filtered location: Poor accuracy " + accuracy + "m");
+            shouldFilter = true;
+        }
+
+        // Filter based on unrealistically high speeds 
+        if (speed > MAX_SPEED_THRESHOLD) {
+            Log.d(TAG, "Filtered location: Unrealistic speed " + speed + "m/s");
+            shouldFilter = true;
+        }
+
+        // Filter based on large jumps when accuracy is moderate or poor
+        if (distance > MAX_DISTANCE_JUMP && accuracy > 75.0f) {
+            Log.d(TAG, "Filtered location: Large jump with poor accuracy - distance: " 
+                + distance + "m, accuracy: " + accuracy + "m");
+            shouldFilter = true;
+        }
+
+        // Accept and update reference if it passes filters
+        if (!shouldFilter) {
+            lastFilteredLocation = newLocation;
+        }
+
+        return !shouldFilter;
+    }
+
+    /**
+     * Resets the internal state of the filter.
+     * This should be called when location updates are stopped.
+     */
+    public static void reset() {
+        lastFilteredLocation = null;
+    }
+} 

geolocator_android/android/src/main/java/com/baseflow/geolocator/location/LocationManagerClient.java

@@ -170,6 +170,11 @@ public void startPositionUpdates(
           ? LocationRequestCompat.PASSIVE_INTERVAL
           : locationOptions.getTimeInterval();
       quality = accuracyToQuality(accuracy);
+      
+      // Enable or disable the location accuracy filter based on options
+      LocationAccuracyFilter.setFilterEnabled(locationOptions.isEnableAccuracyFilter());
+    } else {
+      LocationAccuracyFilter.setFilterEnabled(false);
     }
 
     this.currentLocationProvider = determineProvider(this.locationManager, accuracy);
@@ -202,11 +207,12 @@ public void stopPositionUpdates() {
     this.isListening = false;
     this.nmeaClient.stop();
     this.locationManager.removeUpdates(this);
+    LocationAccuracyFilter.reset();
   }
 
   @Override
   public synchronized void onLocationChanged(Location location) {
-    if (isBetterLocation(location, currentBestLocation)) {
+    if (isBetterLocation(location, currentBestLocation) && LocationAccuracyFilter.shouldAcceptLocation(location)) {
       this.currentBestLocation = location;
 
       if (this.positionChangedCallback != null) {

geolocator_android/android/src/main/java/com/baseflow/geolocator/location/LocationOptions.java

@@ -9,24 +9,27 @@ public class LocationOptions {
   private final long distanceFilter;
   private final long timeInterval;
   private final boolean useMSLAltitude;
+  private final boolean enableAccuracyFilter;
 
   private LocationOptions(
-      LocationAccuracy accuracy, long distanceFilter, long timeInterval, boolean useMSLAltitude) {
+      LocationAccuracy accuracy, long distanceFilter, long timeInterval, boolean useMSLAltitude, boolean enableAccuracyFilter) {
     this.accuracy = accuracy;
     this.distanceFilter = distanceFilter;
     this.timeInterval = timeInterval;
     this.useMSLAltitude = useMSLAltitude;
+    this.enableAccuracyFilter = enableAccuracyFilter;
   }
 
   public static LocationOptions parseArguments(Map<String, Object> arguments) {
     if (arguments == null) {
-      return new LocationOptions(LocationAccuracy.best, 0, 5000, false);
+      return new LocationOptions(LocationAccuracy.best, 0, 5000, false, false);
     }
 
     final Integer accuracy = (Integer) arguments.get("accuracy");
     final Integer distanceFilter = (Integer) arguments.get("distanceFilter");
     final Integer timeInterval = (Integer) arguments.get("timeInterval");
     final Boolean useMSLAltitude = (Boolean) arguments.get("useMSLAltitude");
+    final Boolean enableAccuracyFilter = (Boolean) arguments.get("enableAccuracyFilter");
 
     LocationAccuracy locationAccuracy = LocationAccuracy.best;
 
@@ -57,7 +60,8 @@ public static LocationOptions parseArguments(Map<String, Object> arguments) {
         locationAccuracy,
         distanceFilter != null ? distanceFilter : 0,
         timeInterval != null ? timeInterval : 5000,
-        useMSLAltitude != null && useMSLAltitude);
+        useMSLAltitude != null && useMSLAltitude,
+        enableAccuracyFilter != null && enableAccuracyFilter);
   }
 
   public LocationAccuracy getAccuracy() {
@@ -75,4 +79,8 @@ public long getTimeInterval() {
   public boolean isUseMSLAltitude() {
     return useMSLAltitude;
   }
+
+  public boolean isEnableAccuracyFilter() {
+    return enableAccuracyFilter;
+  }
 }