Altitude correction of workout samples

NOTICE.md

@@ -49,6 +49,30 @@
     See the License for the specific language governing permissions and
     limitations under the License.
 
+<https://github.com/vectorstofinal/geoid_heights>
+
+    The MIT License (MIT)
+
+    Copyright (c) 2015 vectorstofinal
+
+    Permission is hereby granted, free of charge, to any person obtaining a copy
+    of this software and associated documentation files (the "Software"), to deal
+    in the Software without restriction, including without limitation the rights
+    to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+    copies of the Software, and to permit persons to whom the Software is
+    furnished to do so, subject to the following conditions:
+
+    The above copyright notice and this permission notice shall be included in all
+    copies or substantial portions of the Software.
+
+    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+    AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+    SOFTWARE.
+
 <https://github.com/westnordost/osmapi>
 
     © 2016-2019 Tobias Zwick. This library is released under the terms of the GNU Lesser General Public License (LGPL).

app/src/main/java/de/tadris/fitness/recording/WorkoutSaver.java

@@ -23,12 +23,14 @@ import android.content.Context;
 import android.hardware.SensorManager;
 import android.util.Log;
 
+import java.io.IOException;
 import java.util.List;
 
 import de.tadris.fitness.Instance;
 import de.tadris.fitness.data.AppDatabase;
 import de.tadris.fitness.data.Workout;
 import de.tadris.fitness.data.WorkoutSample;
+import de.tadris.fitness.util.AltitudeCorrection;
 import de.tadris.fitness.util.CalorieCalculator;
 
 class WorkoutSaver {
@@ -51,7 +53,7 @@ class WorkoutSaver {
         setSimpleValues();
         setTopSpeed();
 
-        setRealElevation();
+        setElevation();
         setAscentAndDescent();
 
         setCalories();
@@ -101,7 +103,27 @@ class WorkoutSaver {
         workout.topSpeed= topSpeed;
     }
 
-    private void setRealElevation(){
+    private void setElevation() {
+        setCorrectedElevation();
+        setPressureElevation();
+    }
+
+    private void setCorrectedElevation() {
+        // Please see the AltitudeCorrection.java for the reason of this
+        try {
+            int lat = (int) Math.round(samples.get(0).lat);
+            int lon = (int) Math.round(samples.get(0).lon);
+            AltitudeCorrection correction = new AltitudeCorrection(context, lat, lon);
+            for (WorkoutSample sample : samples) {
+                sample.elevation = correction.getHeightOverSeaLevel(sample.elevation);
+            }
+        } catch (IOException e) {
+            // If we can't read the file, we cannot correct the values
+            e.printStackTrace();
+        }
+    }
+
+    private void setPressureElevation() {
         boolean pressureDataAvailable= samples.get(0).tmpPressure != -1;
 
         if(!pressureDataAvailable){

app/src/main/java/de/tadris/fitness/util/AltitudeCorrection.java

@@ -0,0 +1,57 @@
+package de.tadris.fitness.util;
+
+import android.content.Context;
+
+import org.apache.commons.io.IOUtils;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.nio.charset.StandardCharsets;
+import java.util.List;
+
+import de.tadris.fitness.R;
+
+/**
+ * This class has the task to correct the altitude.
+ * <p>
+ * In Germany or UK for example the GPS height differs
+ * roughly 50m from the real elevation over sea level.
+ * <p>
+ * The altitude given by GPS is the altitude over the WGS84 reference ellipsoid
+ * but we want the height over the sea level. That's why we have to correct the height.
+ * Luckily I found a file containing the corrections for all places around the world.
+ * <p>
+ * The geoids.csv is from https://github.com/vectorstofinal/geoid_heights licensed under MIT
+ */
+public class AltitudeCorrection {
+
+    private Context context;
+    private int latitude, longitude;
+    private double offset; // Basically how much higher the sea-level than the ellipsoid is
+
+    public AltitudeCorrection(Context context, int latitude, int longitude) throws IOException {
+        this.context = context;
+        this.latitude = latitude;
+        this.longitude = longitude;
+        findOffset();
+    }
+
+    private void findOffset() throws IOException {
+        InputStream inputStream = context.getResources().openRawResource(R.raw.geoids);
+        List<String> list = IOUtils.readLines(inputStream, StandardCharsets.UTF_8);
+        for (String line : list) {
+            String[] data = line.split(",");
+            int lat = Integer.parseInt(data[0]);
+            int lon = Integer.parseInt(data[1]);
+            double offset = Integer.parseInt(data[2]);
+            if (lat == this.latitude && lon == this.longitude) {
+                this.offset = offset;
+                return;
+            }
+        }
+    }
+
+    public double getHeightOverSeaLevel(double heightOverEllipsoid) {
+        return heightOverEllipsoid - offset;
+    }
+}