Implement elevation gain via barometer.

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

@@ -0,0 +1,49 @@
+package de.dennisguse.opentracks.util;
+
+import android.hardware.SensorManager;
+
+public class PressureSensorUtils {
+
+    //Everything above is considered a meaningful change in elevation.
+    private static float ELEVATION_CHANGE_DIFF_M = 5.0f;
+
+    private PressureSensorUtils() {
+    }
+
+    public static class ElevationChange {
+
+        private float currentSensorValue_hPa;
+
+        private float elevationChange_m;
+
+        public ElevationChange(float currentSensorValue_hPa, float elevationChange_m) {
+            this.currentSensorValue_hPa = currentSensorValue_hPa;
+            this.elevationChange_m = elevationChange_m;
+        }
+
+        public float getCurrentSensorValue_hPa() {
+            return currentSensorValue_hPa;
+        }
+
+        public float getElevationChange_m() {
+            return elevationChange_m;
+        }
+    }
+
+    /**
+     * Computes the elevation gain and elevation loss.
+     *
+     * @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);
+        float currentSensorValue_m = SensorManager.getAltitude(SensorManager.PRESSURE_STANDARD_ATMOSPHERE, currentSensorValue_hPa);
+
+        float elevationChange_m = currentSensorValue_m - lastSensorValue_m;
+        if (Math.abs(elevationChange_m) < ELEVATION_CHANGE_DIFF_M) {
+            return null;
+        }
+
+        return new ElevationChange(currentSensorValue_hPa, elevationChange_m);
+    }
+}