Elevation gain: apply exponential smoothing and limit changes (defined change diff per sensor value).

src/androidTest/java/de/dennisguse/opentracks/util/PressureSensorUtilsTest.java

@@ -20,10 +20,11 @@ public class PressureSensorUtilsTest {
         }
     }
 
+    // Simulate a sudden drop of elevation.
     // test data
     @Test
     public void computeChanges_downhill() {
-        float[] sensorValues_hPa = new float[]{1015f, 1015.01f, 1015.02f, 1015.03f, 1015.04f, 1015.05f, 1015.06f, 1015.07f, 1015.08f, 1015.09f, 1015.10f, 1015.11f, 1015.12f, 1015.13f, 1015.14f, 1015.15f};
+        float[] sensorValues_hPa = new float[]{1015f, 1015.01f, 1015.02f, 1015.03f, 1015.04f, 1015.05f, 1015.06f, 1015.07f, 1015.08f, 1015.09f, 1015.10f, 1015.11f, 1015.12f, 1015.13f, 1018f, 1018.1f, 1018.1f, 1018.1f, 1018.1f};
         float firstSensorValue = sensorValues_hPa[0];
 
         // when
@@ -34,18 +35,15 @@ public class PressureSensorUtilsTest {
         for (float v : sensorValues_hPa) {
             PressureSensorUtils.ElevationChange elevationChange = PressureSensorUtils.computeChanges_m(lastUsedPressureValue_hPa, v);
             if (elevationChange != null) {
-                if (elevationChange.getElevationChange_m() > 0) {
-                    elevationGain_m += elevationChange.getElevationChange_m();
-                } else {
-                    elevationLoss_m += elevationChange.getElevationChange_m();
-                }
+                elevationGain_m += elevationChange.getElevationGain_m();
+                elevationLoss_m += elevationChange.getElevationLoss_m();
                 lastUsedPressureValue_hPa = elevationChange.getCurrentSensorValue_hPa();
             }
         }
 
         // then
         assertEquals(0f, elevationGain_m, 0.01);
-        assertEquals(-1.08f, elevationLoss_m, 0.01);
-        assertEquals(1015.13, lastUsedPressureValue_hPa, 0.01);
+        assertEquals(-25.0f, elevationLoss_m, 0.01);
+        assertEquals(1018.01f, lastUsedPressureValue_hPa, 0.01);
     }
 }

src/main/java/de/dennisguse/opentracks/fragments/StatisticsRecordedFragment.java

@@ -135,8 +135,6 @@ public class StatisticsRecordedFragment extends Fragment {
         speedMovingValue = view.findViewById(R.id.stats_moving_speed_value);
         speedMovingUnit = view.findViewById(R.id.stats_moving_speed_unit);
 
-        elevationCurrentGroup = view.findViewById(R.id.stats_elevation_current_group);
-
         elevationTotalGainValue = view.findViewById(R.id.stats_elevation_gain_value);
         elevationTotalGainUnit = view.findViewById(R.id.stats_elevation_gain_unit);
     }

src/main/java/de/dennisguse/opentracks/services/sensors/ElevationSumManager.java

@@ -23,7 +23,9 @@ public class ElevationSumManager implements SensorEventListener {
 
     private boolean isConnected = false;
 
-    private float lastUsedPressureValue_hPa;
+    private float lastAcceptedPressureValue_hPa;
+
+    private float lastSeenSensorValue_hPa;
 
     private float elevationGain_m;
     private float elevationLoss_m;
@@ -38,7 +40,7 @@ public class ElevationSumManager implements SensorEventListener {
         }
 
         isConnected = sensorManager.registerListener(this, pressureSensor, SAMPLING_RATE);
-        lastUsedPressureValue_hPa = Float.NaN;
+        lastAcceptedPressureValue_hPa = Float.NaN;
         reset();
     }
 
@@ -82,21 +84,21 @@ public class ElevationSumManager implements SensorEventListener {
 
     @VisibleForTesting
     void onSensorValueChanged(float value_hPa) {
-        if (Float.isNaN(lastUsedPressureValue_hPa)) {
-            lastUsedPressureValue_hPa = value_hPa;
+        if (Float.isNaN(lastAcceptedPressureValue_hPa)) {
+            lastAcceptedPressureValue_hPa = value_hPa;
+            lastSeenSensorValue_hPa = value_hPa;
             return;
         }
 
-        PressureSensorUtils.ElevationChange elevationChange = PressureSensorUtils.computeChanges_m(lastUsedPressureValue_hPa, value_hPa);
+        PressureSensorUtils.ElevationChange elevationChange = PressureSensorUtils.computeChangesWithSmoothing_m(lastAcceptedPressureValue_hPa, lastSeenSensorValue_hPa, value_hPa);
         if (elevationChange != null) {
-            if (elevationChange.getElevationChange_m() > 0) {
-                elevationGain_m += elevationChange.getElevationChange_m();
-            } else {
-                elevationLoss_m += elevationChange.getElevationChange_m();
-            }
-            lastUsedPressureValue_hPa = elevationChange.getCurrentSensorValue_hPa();
+            elevationGain_m += elevationChange.getElevationGain_m();
+            elevationLoss_m += elevationChange.getElevationLoss_m();
+            lastAcceptedPressureValue_hPa = elevationChange.getCurrentSensorValue_hPa();
         }
 
+        lastSeenSensorValue_hPa = value_hPa;
+
         Log.v(TAG, "elevation gain: " + elevationGain_m);
     }
 }

src/main/java/de/dennisguse/opentracks/util/PressureSensorUtils.java

@@ -7,6 +7,8 @@ public class PressureSensorUtils {
     //Everything above is considered a meaningful change in elevation.
     private static float ELEVATION_CHANGE_DIFF_M = 5.0f;
 
+    private static float EXPONENTIAL_SMOOTHING = 0.3f;
+
     private PressureSensorUtils() {
     }
 
@@ -28,6 +30,23 @@ public class PressureSensorUtils {
         public float getElevationChange_m() {
             return elevationChange_m;
         }
+
+        public float getElevationGain_m() {
+            return elevationChange_m > 0 ? elevationChange_m : 0;
+        }
+
+        public float getElevationLoss_m() {
+            return elevationChange_m < 0 ? elevationChange_m : 0;
+        }
+    }
+
+    /**
+     * Applies exponential smoothing to sensor value before computation.
+     */
+    public static ElevationChange computeChangesWithSmoothing_m(float lastAcceptedSensorValue_hPa, float lastSeenSensorValue_hPa, float currentSensorValue_hPa) {
+        float nextSensorValue_hPa = EXPONENTIAL_SMOOTHING * currentSensorValue_hPa + (1 - EXPONENTIAL_SMOOTHING) * lastSeenSensorValue_hPa;
+
+        return computeChanges_m(lastAcceptedSensorValue_hPa, nextSensorValue_hPa);
     }
 
     /**
@@ -35,8 +54,8 @@ public class PressureSensorUtils {
      *
      * @return null if no meaningful elevation change occurred.
      */
-    public static ElevationChange computeChanges_m(float lastSensorValue_hPa, float currentSensorValue_hPa) {
-        float lastSensorValue_m = SensorManager.getAltitude(SensorManager.PRESSURE_STANDARD_ATMOSPHERE, lastSensorValue_hPa);
+    public static ElevationChange computeChanges_m(float lastAcceptedSensorValue_hPa, float currentSensorValue_hPa) {
+        float lastSensorValue_m = SensorManager.getAltitude(SensorManager.PRESSURE_STANDARD_ATMOSPHERE, lastAcceptedSensorValue_hPa);
         float currentSensorValue_m = SensorManager.getAltitude(SensorManager.PRESSURE_STANDARD_ATMOSPHERE, currentSensorValue_hPa);
 
         float elevationChange_m = currentSensorValue_m - lastSensorValue_m;
@@ -44,6 +63,21 @@ public class PressureSensorUtils {
             return null;
         }
 
-        return new ElevationChange(currentSensorValue_hPa, elevationChange_m);
+        // Limit elevation change by ELEVATION_CHANGE_DIFF and computes pressure value accordingly.
+        ElevationChange elevationChange = new ElevationChange(currentSensorValue_hPa, elevationChange_m);
+        if (elevationChange.getElevationGain_m() > 0) {
+            return new ElevationChange(getBarometricPressure(SensorManager.PRESSURE_STANDARD_ATMOSPHERE, lastSensorValue_m + ELEVATION_CHANGE_DIFF_M), ELEVATION_CHANGE_DIFF_M);
+        } else {
+            return new ElevationChange(getBarometricPressure(SensorManager.PRESSURE_STANDARD_ATMOSPHERE, lastSensorValue_m - ELEVATION_CHANGE_DIFF_M), -1 * ELEVATION_CHANGE_DIFF_M);
+        }
+    }
+
+    /*
+     * Barometeric pressure to elevation estimation; inverts of SensorManager.getAltitude(float, float)
+     * https://de.wikipedia.org/wiki/Barometrische_H%C3%B6henformel#Internationale_H%C3%B6henformel
+     * {\color{White} p(h)} = p_0 \cdot \left( 1 - \frac{0{,}0065 \frac{\mathrm K}{\mathrm m} \cdot h}{T_0\ } \right)^{5{,}255}
+     */
+    private static float getBarometricPressure(float p0, float altitude_m) {
+        return (float) (p0 * Math.pow(1.0 - 0.0065 * altitude_m / 288.15, 5.255f));
     }
 }