Smoothen speed values by using data from two consecutive locations

mjaakko · Jan 17, 2025 · 5587e80 · 5587e80
1 parent 3df72ab
commit 5587e80
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Showing 5 changed files with 74 additions and 10 deletions.
diff --git a/app/src/main/java/xyz/malkki/neostumbler/extensions/flowExtensions.kt b/app/src/main/java/xyz/malkki/neostumbler/extensions/flowExtensions.kt
@@ -8,8 +8,10 @@ import kotlinx.coroutines.flow.Flow
 import kotlinx.coroutines.flow.buffer
 import kotlinx.coroutines.flow.channelFlow
 import kotlinx.coroutines.flow.conflate
+import kotlinx.coroutines.flow.filter
 import kotlinx.coroutines.flow.flowOn
 import kotlinx.coroutines.flow.map
+import kotlinx.coroutines.flow.scan
 import kotlinx.coroutines.flow.transform
 import kotlinx.coroutines.flow.transformLatest
 import kotlinx.coroutines.launch
@@ -99,4 +101,10 @@ fun <T> Flow<T>.maxAge(duration: Duration): Flow<T?> = transformLatest { value -
     emit(value)
     delay(duration)
     emit(null)
-}
+}
+
+fun <T> Flow<T>.pairwise(): Flow<Pair<T, T>> = scan(Pair<T?, T?>(null, null)) { pair, value ->
+        pair.second to value
+    }
+    .filter { it.first != null && it.second != null }
+    .map { it.first!! to it.second!! }
diff --git a/app/src/main/java/xyz/malkki/neostumbler/scanner/ScannerService.kt b/app/src/main/java/xyz/malkki/neostumbler/scanner/ScannerService.kt
@@ -66,6 +66,7 @@ import xyz.malkki.neostumbler.scanner.source.BluetoothBeaconSource
 import xyz.malkki.neostumbler.scanner.source.CellInfoSource
 import xyz.malkki.neostumbler.scanner.source.MultiSubscriptionCellInfoSource
 import xyz.malkki.neostumbler.scanner.source.PressureSensorAirPressureSource
+import xyz.malkki.neostumbler.scanner.source.SmoothenedGpsSpeedSource
 import xyz.malkki.neostumbler.scanner.source.TelephonyManagerCellInfoSource
 import xyz.malkki.neostumbler.scanner.source.WifiManagerWifiAccessPointSource
 import xyz.malkki.neostumbler.utils.GpsStats
@@ -218,13 +219,7 @@ class ScannerService : Service() {
                 started = SharingStarted.WhileSubscribed()
             )
 
-        val speedFlow = locationFlow.map {
-            if (it.location.hasSpeed()) {
-                it.location.speed
-            } else {
-                0.0f
-            }
-        }
+        val speedFlow = SmoothenedGpsSpeedSource(locationFlow.map { it.location }).getSpeedFlow()
 
         val cellInfoSource = getCellInfoSource()
 
@@ -273,15 +268,17 @@ class ScannerService : Service() {
                     locationFlow
                 },
                 cellInfoSource = {
-                    val scanFrequencyFlow = speedFlow.map { speed -> (cellScanDistance.toDouble() / speed).seconds }
+                    val scanFrequencyFlow = speedFlow
+                        .map { speed -> (cellScanDistance.toDouble() / speed).seconds }
 
                     cellInfoSource.getCellInfoFlow(scanFrequencyFlow)
                 },
                 bluetoothBeaconSource = {
                     bluetoothBeaconSource.getBluetoothBeaconFlow()
                 },
                 wifiAccessPointSource = {
-                    val scanFrequencyFlow = speedFlow.map { speed -> (wifiScanDistance.toDouble() / speed).seconds }
+                    val scanFrequencyFlow = speedFlow
+                        .map { speed -> (wifiScanDistance.toDouble() / speed).seconds }
 
                     wifiAccessPointSource.getWifiAccessPointFlow(scanFrequencyFlow)
                 },

diff --git a/app/src/main/java/xyz/malkki/neostumbler/scanner/source/SmoothenedGpsSpeedSource.kt b/app/src/main/java/xyz/malkki/neostumbler/scanner/source/SmoothenedGpsSpeedSource.kt
@@ -0,0 +1,40 @@
+package xyz.malkki.neostumbler.scanner.source
+
+import android.location.Location
+import kotlinx.coroutines.flow.Flow
+import kotlinx.coroutines.flow.map
+import xyz.malkki.neostumbler.extensions.elapsedRealtimeMillisCompat
+import xyz.malkki.neostumbler.extensions.pairwise
+import xyz.malkki.neostumbler.scanner.speed.SpeedSource
+import kotlin.math.abs
+import kotlin.time.Duration.Companion.milliseconds
+import kotlin.time.Duration.Companion.seconds
+
+//Maximum age difference between two consecutive locations
+private val LOCATION_MAX_AGE_DIFF = 5.seconds
+
+//Smoothening factor, i.e. how much to weight previous speed vs. current speed
+private const val A = 0.15
+private const val B = 1 - A
+
+/**
+ * Calculates smoothened speed by using data from two consecutive locations
+ */
+class SmoothenedGpsSpeedSource(private val locationFlow: Flow<Location>) : SpeedSource {
+    override fun getSpeedFlow(): Flow<Double> {
+        return locationFlow
+            .pairwise()
+            .map { (prevLocation, currentLocation) ->
+                if (currentLocation.hasSpeed()) {
+                    //Smoothen the speed value by using data from two consecutive locations
+                    if (prevLocation.hasSpeed() && abs(prevLocation.elapsedRealtimeMillisCompat - currentLocation.elapsedRealtimeMillisCompat).milliseconds <= LOCATION_MAX_AGE_DIFF) {
+                        prevLocation.speed * A + currentLocation.speed * B
+                    } else {
+                        currentLocation.speed.toDouble()
+                    }
+                } else {
+                    0.0
+                }
+            }
+    }
+}
diff --git a/app/src/main/java/xyz/malkki/neostumbler/scanner/speed/SpeedSource.kt b/app/src/main/java/xyz/malkki/neostumbler/scanner/speed/SpeedSource.kt
@@ -0,0 +1,10 @@
+package xyz.malkki.neostumbler.scanner.speed
+
+import kotlinx.coroutines.flow.Flow
+
+fun interface SpeedSource {
+    /**
+     * @return Flow emitting the speed in meters per second
+     */
+    fun getSpeedFlow(): Flow<Double>
+}
diff --git a/app/src/test/java/xyz/malkki/neostumbler/extensions/FlowExtensionsTest.kt b/app/src/test/java/xyz/malkki/neostumbler/extensions/FlowExtensionsTest.kt
@@ -129,4 +129,13 @@ class FlowExtensionsTest {
 
         assertEquals(listOf(1, null, 2, null), values)
     }
+
+    @Test
+    fun `Test collecting flow values pairwise`() = runBlocking {
+        val a = flowOf(1, 2, 3)
+
+        val values = a.pairwise().toList()
+
+        assertEquals(listOf(1 to 2, 2 to 3), values)
+    }
 }