Clean up classes in the stats package

- TripStatisticsBuilder
- TripStatistics
- ExtremityMonitor
- DoubleBuffer

MyTracks/src/com/google/android/apps/mytracks/io/file/GpxImporter.java

@@ -306,7 +306,7 @@ public class GpxImporter extends DefaultHandler {
       tripStatisticsBuilder = new TripStatisticsBuilder(0);
       tripStatisticsBuilder.pauseAt(0);
     }
-    track.setTripStatistics(tripStatisticsBuilder.getStatistics());
+    track.setTripStatistics(tripStatisticsBuilder.getTripStatistics());
     track.setNumberOfPoints(numberOfLocations);
     myTracksProviderUtils.updateTrack(track);
     tracksIds.add(track.getId());

MyTracks/src/com/google/android/apps/mytracks/io/fusiontables/SendFusionTablesAsyncTask.java

@@ -253,7 +253,7 @@ public class SendFusionTablesAsyncTask extends AbstractSendAsyncTask {
           elevationBuffer.setNext(metricUnits ? location.getAltitude()
               : location.getAltitude() * UnitConversions.M_TO_FT);
           if (i % elevationSamplingFrequency == 0) {
-            distances.add(tripStatisticsBuilder.getStatistics().getTotalDistance());
+            distances.add(tripStatisticsBuilder.getTripStatistics().getTotalDistance());
             elevations.add(elevationBuffer.getAverage());
           }
           lastLocation = location;
@@ -279,7 +279,7 @@ public class SendFusionTablesAsyncTask extends AbstractSendAsyncTask {
 
       // Create an end marker
       if (lastLocation != null) {
-        distances.add(tripStatisticsBuilder.getStatistics().getTotalDistance());
+        distances.add(tripStatisticsBuilder.getTripStatistics().getTotalDistance());
         elevations.add(elevationBuffer.getAverage());
         DescriptionGenerator descriptionGenerator = new DescriptionGeneratorImpl(context);
         track.setDescription(

MyTracks/src/com/google/android/apps/mytracks/io/maps/SendMapsAsyncTask.java

@@ -297,7 +297,7 @@ public class SendMapsAsyncTask extends AbstractSendAsyncTask {
           elevationBuffer.setNext(metricUnits ? location.getAltitude()
               : location.getAltitude() * UnitConversions.M_TO_FT);
           if (i % elevationSamplingFrequency == 0) {
-            distances.add(tripStatisticsBuilder.getStatistics().getTotalDistance());
+            distances.add(tripStatisticsBuilder.getTripStatistics().getTotalDistance());
             elevations.add(elevationBuffer.getAverage());
           }
           lastLocation = location;
@@ -323,7 +323,7 @@ public class SendMapsAsyncTask extends AbstractSendAsyncTask {
 
       // Create an end marker
       if (lastLocation != null) {
-        distances.add(tripStatisticsBuilder.getStatistics().getTotalDistance());
+        distances.add(tripStatisticsBuilder.getTripStatistics().getTotalDistance());
         elevations.add(elevationBuffer.getAverage());
         
         track.setDescription(getTrackDescription(track, distances, elevations));

MyTracks/src/com/google/android/apps/mytracks/services/TrackRecordingService.java

@@ -654,7 +654,7 @@ public class TrackRecordingService extends Service {
             }
           } while (cursor.moveToPrevious());
         }
-        statsBuilder.getStatistics().setMovingTime(stats.getMovingTime());
+        statsBuilder.getTripStatistics().setMovingTime(stats.getMovingTime());
         statsBuilder.pauseAt(stats.getStopTime());
         statsBuilder.resumeAt(System.currentTimeMillis());
       } else {
@@ -834,7 +834,7 @@ public class TrackRecordingService extends Service {
 
       // Update the current track:
       if (lastRecordedLocation != null && lastRecordedLocation.getLatitude() < 90) {
-        TripStatistics tripStatistics = statsBuilder.getStatistics();
+        TripStatistics tripStatistics = statsBuilder.getTripStatistics();
         tripStatistics.setStopTime(System.currentTimeMillis());
         
         if (recordingTrack.getStartId() < 0) {
@@ -865,8 +865,8 @@ public class TrackRecordingService extends Service {
       if (waypoint != null) {
         waypoint.setLength(length);
         waypoint.setDuration(
-            System.currentTimeMillis() - statsBuilder.getStatistics().getStartTime());
-        waypoint.setTripStatistics(waypointStatsBuilder.getStatistics());
+            System.currentTimeMillis() - statsBuilder.getTripStatistics().getStartTime());
+        waypoint.setTripStatistics(waypointStatsBuilder.getTripStatistics());
         providerUtils.updateWaypoint(waypoint);
       }
     }
@@ -896,7 +896,7 @@ public class TrackRecordingService extends Service {
     }
     waypoint.setTrackId(recordingTrackId);
     waypoint.setLength(length);
-    if (lastLocation == null || statsBuilder == null || statsBuilder.getStatistics() == null) {
+    if (lastLocation == null || statsBuilder == null || statsBuilder.getTripStatistics() == null) {
       if (!request.isTrackStatistics()) {
         return -1L;
       }
@@ -910,7 +910,7 @@ public class TrackRecordingService extends Service {
       waypoint.setLocation(location);
     } else {
       waypoint.setLocation(lastLocation);
-      waypoint.setDuration(lastLocation.getTime() - statsBuilder.getStatistics().getStartTime());
+      waypoint.setDuration(lastLocation.getTime() - statsBuilder.getTripStatistics().getStartTime());
     }
     Uri uri = providerUtils.insertWaypoint(waypoint);
     return Long.parseLong(uri.getLastPathSegment());
@@ -958,7 +958,7 @@ public class TrackRecordingService extends Service {
 
     // Override the duration - it's not the duration from the last waypoint, but
     // the duration from the beginning of the whole track
-    waypoint.setDuration(time - statsBuilder.getStatistics().getStartTime());
+    waypoint.setDuration(time - statsBuilder.getTripStatistics().getStartTime());
 
     // Set the rest of the waypoint data
     waypoint.setType(Waypoint.TYPE_STATISTICS);
@@ -973,7 +973,7 @@ public class TrackRecordingService extends Service {
       name = getString(R.string.marker_split_name_format, nextMarkerNumber);
     }
     waypoint.setName(name);
-    waypoint.setTripStatistics(waypointStatsBuilder.getStatistics());
+    waypoint.setTripStatistics(waypointStatsBuilder.getTripStatistics());
     waypoint.setDescription(descriptionGenerator.generateWaypointDescription(waypoint));
     waypoint.setIcon(getString(R.string.marker_statistics_icon_url));
 
@@ -1050,7 +1050,7 @@ public class TrackRecordingService extends Service {
   }
 
   public TripStatistics getTripStatistics() {
-    return statsBuilder.getStatistics();
+    return statsBuilder.getTripStatistics();
   }
 
   Location getLastLocation() {

MyTracks/src/com/google/android/apps/mytracks/stats/DoubleBuffer.java

@@ -20,66 +20,35 @@ package com.google.android.apps.mytracks.stats;
  * This class maintains a buffer of doubles. This buffer is a convenient class
  * for storing a series of doubles and calculating information about them. This
  * is a FIFO buffer.
- *
+ * 
  * @author Sandor Dornbush
  */
 public class DoubleBuffer {
 
-  /**
-   * The location that the next write will occur at.
-   */
+  // The location that the next write will occur at.
   private int index;
 
-  /**
-   * The sliding buffer of doubles.
-   */
+  // The sliding buffer of doubles.
   private final double[] buffer;
 
-  /**
-   * Have all of the slots in the buffer been filled?
-   */
+  // True if the buffer is full
   private boolean isFull;
 
   /**
-   * Creates a buffer with size elements.
-   *
-   * @param size the number of elements in the buffer
-   * @throws IllegalArgumentException if the size is not a positive value
+   * Creates a buffer with a certain size.
+   * 
+   * @param size the size
    */
   public DoubleBuffer(int size) {
     if (size < 1) {
-      throw new IllegalArgumentException("The buffer size must be positive.");
+      throw new IllegalArgumentException("The buffer size must be greater than 1.");
     }
     buffer = new double[size];
     reset();
   }
 
   /**
-   * Adds a double to the buffer. If the buffer is full the oldest element is
-   * overwritten.
-   *
-   * @param d the double to add
-   */
-  public void setNext(double d) {
-    if (index == buffer.length) {
-      index = 0;
-    }
-    buffer[index] = d;
-    index++;
-    if (index == buffer.length) {
-      isFull = true;
-    }
-  }
-
-  /**
-   * Are all of the entries in the buffer used?
-   */
-  public boolean isFull() {
-    return isFull;
-  }
-
-  /**
-   * Resets the buffer to the initial state.
+   * Resets the buffer.
    */
   public void reset() {
     index = 0;
@@ -87,16 +56,20 @@ public class DoubleBuffer {
   }
 
   /**
-   * Gets the average of values from the buffer.
-   *
-   * @return The average of the buffer
+   * Returns true if the buffer is full.
+   */
+  public boolean isFull() {
+    return isFull;
+  }
+
+  /**
+   * Gets the average of the buffer.
    */
   public double getAverage() {
     int numberOfEntries = isFull ? buffer.length : index;
     if (numberOfEntries == 0) {
       return 0;
     }
-
     double sum = 0;
     for (int i = 0; i < numberOfEntries; i++) {
       sum += buffer[i];
@@ -105,15 +78,15 @@ public class DoubleBuffer {
   }
 
   /**
-   * Gets the average and standard deviation of the buffer.
-   *
-   * @return An array of two elements - the first is the average, and the second
-   *         is the variance
+   * Gets the average and the variance of the buffer.
+   * 
+   * @return an array of two elements - the first is the average, the second is
+   *         the variance
    */
   public double[] getAverageAndVariance() {
     int numberOfEntries = isFull ? buffer.length : index;
     if (numberOfEntries == 0) {
-      return new double[]{0, 0};
+      return new double[] { 0, 0 };
     }
 
     double sum = 0;
@@ -124,8 +97,25 @@ public class DoubleBuffer {
     }
 
     double average = sum / numberOfEntries;
-    return new double[]{average,
-      sumSquares / numberOfEntries  - Math.pow(average, 2)};
+    double variance = sumSquares / numberOfEntries - Math.pow(average, 2);
+    return new double[] { average, variance };
+  }
+
+  /**
+   * Adds a double to the buffer. If the buffer is full the oldest element is
+   * overwritten.
+   * 
+   * @param value the double to add
+   */
+  public void setNext(double value) {
+    if (index == buffer.length) {
+      index = 0;
+    }
+    buffer[index] = value;
+    index++;
+    if (index == buffer.length) {
+      isFull = true;
+    }
   }
 
   @Override

MyTracks/src/com/google/android/apps/mytracks/stats/TripStatisticsBuilder.java

@@ -20,352 +20,307 @@ import static com.google.android.apps.mytracks.Constants.TAG;
 
 import com.google.android.apps.mytracks.Constants;
 import com.google.android.apps.mytracks.util.PreferencesUtils;
+import com.google.common.annotations.VisibleForTesting;
 
 import android.location.Location;
 import android.util.Log;
 
 /**
- * Statistics keeper for a trip.
+ * Builder for {@link TripStatistics}. For keeping statistics as a track is
+ * paused/resumed and new locations are added.
  * 
  * @author Sandor Dornbush
  * @author Rodrigo Damazio
  */
 public class TripStatisticsBuilder {
-  /**
-   * Statistical data about the trip, which can be displayed to the user.
-   */
-  private final TripStatistics data;
 
-  /**
-   * The last location that the gps reported.
-   */
-  private Location lastLocation;
-
-  /**
-   * The last location that contributed to the stats. It is also the last
-   * location the user was found to be moving.
-   */
-  private Location lastMovingLocation;
-
-  /**
-   * The current speed in meters/second as reported by the gps.
-   */
-  private double currentSpeed;
-
-  /**
-   * The current grade. This value is very noisy and not reported to the user.
-   */
-  private double currentGrade;
-
-  /**
-   * Is the trip currently paused?
-   * All trips start paused.
-   */
-  private boolean paused = true;
-
-  /**
-   * A buffer of the last speed readings in meters/second.
-   */
-  private final DoubleBuffer speedBuffer =
-      new DoubleBuffer(Constants.SPEED_SMOOTHING_FACTOR);
-
-  /**
-   * A buffer of the recent elevation readings in meters.
-   */
-  private final DoubleBuffer elevationBuffer =
-      new DoubleBuffer(Constants.ELEVATION_SMOOTHING_FACTOR);
-
-  /**
-   * A buffer of the distance between recent gps readings in meters.
-   */
-  private final DoubleBuffer distanceBuffer =
-      new DoubleBuffer(Constants.DISTANCE_SMOOTHING_FACTOR);
-
-  /**
-   * A buffer of the recent grade calculations.
-   */
-  private final DoubleBuffer gradeBuffer =
-      new DoubleBuffer(Constants.GRADE_SMOOTHING_FACTOR);
-
-  /**
-   * The total number of locations in this trip.
-   */
-  private long totalLocations = 0;
+  // The trip statistics.
+  private final TripStatistics tripStatistics;
 
+  // The minimum recording distance.
   private int minRecordingDistance = PreferencesUtils.MIN_RECORDING_DISTANCE_DEFAULT;
 
+  // True if the trip is paused. All trips start as paused.
+  private boolean paused = true;
+
+  // The last location as reported by GPS.
+  private Location lastLocation;
+
+  // The last moving location that contributed to the moving statistics.
+  private Location lastMovingLocation;
+
+  // A buffer of the recent speed readings (m/s) for calculating max speed.
+  private final DoubleBuffer speedBuffer = new DoubleBuffer(Constants.SPEED_SMOOTHING_FACTOR);
+
+  // A buffer of the recent elevation readings (m).
+  private final DoubleBuffer elevationBuffer = new DoubleBuffer(
+      Constants.ELEVATION_SMOOTHING_FACTOR);
+
+  // A buffer of the recent distance readings for calculating grade.
+  private final DoubleBuffer distanceBuffer = new DoubleBuffer(Constants.DISTANCE_SMOOTHING_FACTOR);
+
+  // A buffer of the recent grade calculations
+  private final DoubleBuffer gradeBuffer = new DoubleBuffer(Constants.GRADE_SMOOTHING_FACTOR);
+
   /**
-   * Creates a new trip starting at the given time.
+   * Creates a new trip starting at a start time.
    * 
-   * @param startTime the start time.
+   * @param startTime the start time
    */
   public TripStatisticsBuilder(long startTime) {
-    data = new TripStatistics();
+    tripStatistics = new TripStatistics();
     resumeAt(startTime);
   }
 
   /**
-   * Creates a new trip, starting with existing statistics data.
-   *
-   * @param statsData the statistics data to copy and start from
-   */
-  public TripStatisticsBuilder(TripStatistics statsData) {
-    data = new TripStatistics(statsData);
-    if (data.getStartTime() > 0) {
-      resumeAt(data.getStartTime());
-    }
-  }
-
-  /**
-   * Adds a location to the current trip. This will update all of the internal
-   * variables with this new location.
+   * Creates a new trip, starting with an existing {@link TripStatistics}.
    * 
-   * @param currentLocation the current gps location
-   * @param systemTime the time used for calculation of totalTime. This should
-   *        be the phone's time (not GPS time)
-   * @return true if the person is moving
+   * @param other the existing {@link TripStatistics}
    */
-  public boolean addLocation(Location currentLocation, long systemTime) {
-    if (paused) {
-      Log.w(TAG,
-          "Tried to account for location while track is paused");
-      return false;
+  public TripStatisticsBuilder(TripStatistics other) {
+    tripStatistics = new TripStatistics(other);
+    if (tripStatistics.getStartTime() > 0) {
+      resumeAt(tripStatistics.getStartTime());
     }
-
-    totalLocations++;
-
-    double elevationDifference = updateElevation(currentLocation.getAltitude());
-
-    // Update the "instant" values:
-    data.setTotalTime(systemTime - data.getStartTime());
-    currentSpeed = currentLocation.getSpeed();
-
-    // This was the 1st location added, remember it and do nothing else:
-    if (lastLocation == null) {
-      lastLocation = currentLocation;
-      lastMovingLocation = currentLocation;
-      return false;
-    }
-
-    updateBounds(currentLocation);
-
-    // Don't do anything if we didn't move since last fix:
-    double distance = lastLocation.distanceTo(currentLocation);
-    if (distance < minRecordingDistance &&
-        currentSpeed < Constants.MAX_NO_MOVEMENT_SPEED) {
-      lastLocation = currentLocation;
-      return false;
-    }
-
-    data.addTotalDistance(lastMovingLocation.distanceTo(currentLocation));
-    updateSpeed(currentLocation.getTime(), currentSpeed,
-        lastLocation.getTime(), lastLocation.getSpeed());
-
-    updateGrade(distance, elevationDifference);
-    lastLocation = currentLocation;
-    lastMovingLocation = currentLocation;
-    return true;
   }
 
   /**
-   * Updates the track's bounding box to include the given location.
-   */
-  private void updateBounds(Location location) {
-    data.updateLatitudeExtremities(location.getLatitude());
-    data.updateLongitudeExtremities(location.getLongitude());
-  }
-
-  /**
-   * Updates the elevation measurements.
+   * Sets the min recording distance.
    * 
-   * @param elevation the current elevation
+   * @param minRecordingDistance the min recording distance
    */
-  // @VisibleForTesting
-  double updateElevation(double elevation) {
-    double oldSmoothedElevation = getSmoothedElevation();
-    elevationBuffer.setNext(elevation);
-    double smoothedElevation = getSmoothedElevation();
-    data.updateElevationExtremities(smoothedElevation);
-    double elevationDifference = elevationBuffer.isFull()
-        ? smoothedElevation - oldSmoothedElevation
-        : 0.0;
-    if (elevationDifference > 0) {
-      data.addTotalElevationGain(elevationDifference);
-    }
-    return elevationDifference;
+  public void setMinRecordingDistance(int minRecordingDistance) {
+    this.minRecordingDistance = minRecordingDistance;
   }
 
   /**
-   * Updates the speed measurements.
+   * Resumes the current track at a given time.
    * 
-   * @param updateTime the time of the speed update
-   * @param speed the current speed
-   * @param lastLocationTime the time of the last speed update
-   * @param lastLocationSpeed the speed of the last update
+   * @param time the time
    */
-  // @VisibleForTesting
-  void updateSpeed(long updateTime, double speed, long lastLocationTime,
-      double lastLocationSpeed) {
-    // We are now sure the user is moving.
-    long timeDifference = updateTime - lastLocationTime;
-    if (timeDifference < 0) {
-      Log.e(TAG,
-          "Found negative time change: " + timeDifference);
-    }
-    data.addMovingTime(timeDifference);
-
-    if (isValidSpeed(updateTime, speed, lastLocationTime, lastLocationSpeed,
-        speedBuffer)) {
-      speedBuffer.setNext(speed);
-      if (speed > data.getMaxSpeed()) {
-        data.setMaxSpeed(speed);
-      }
-      double movingSpeed = data.getAverageMovingSpeed();
-      if (speedBuffer.isFull() && (movingSpeed > data.getMaxSpeed())) {
-        data.setMaxSpeed(movingSpeed);
-      }
-    } else {
-      Log.d(TAG,
-          "TripStatistics ignoring big change: Raw Speed: " + speed
-          + " old: " + lastLocationSpeed + " [" + toString() + "]");
-    }
-  }
-
-  /**
-   * Checks to see if this is a valid speed.
-   * 
-   * @param updateTime The time at the current reading
-   * @param speed The current speed
-   * @param lastLocationTime The time at the last location
-   * @param lastLocationSpeed Speed at the last location
-   * @param speedBuffer A buffer of recent readings
-   * @return True if this is likely a valid speed
-   */
-  public static boolean isValidSpeed(long updateTime, double speed,
-      long lastLocationTime, double lastLocationSpeed,
-      DoubleBuffer speedBuffer) {
-
-    // We don't want to count 0 towards the speed.
-    if (speed == 0) {
-      return false;
-    }
-    // We are now sure the user is moving.
-    long timeDifference = updateTime - lastLocationTime;
-
-    // There are a lot of noisy speed readings.
-    // Do the cheapest checks first, most expensive last.
-    // The following code will ignore unlikely to be real readings.
-    // - 128 m/s seems to be an internal android error code.
-    if (Math.abs(speed - 128) < 1) {
-      return false;
-    }
-
-    // Another check for a spurious reading. See if the path seems physically
-    // likely. Ignore any speeds that imply accelaration greater than 2g's
-    // Really who can accelerate faster?
-    double speedDifference = Math.abs(lastLocationSpeed - speed);
-    if (speedDifference > Constants.MAX_ACCELERATION * timeDifference) {
-      return false;
-    }
-
-    // There are three additional checks if the reading gets this far:
-    // - Only use the speed if the buffer is full
-    // - Check that the current speed is less than 10x the recent smoothed speed
-    // - Double check that the current speed does not imply crazy acceleration
-    double smoothedSpeed = speedBuffer.getAverage();
-    double smoothedDiff = Math.abs(smoothedSpeed - speed);
-    return !speedBuffer.isFull() ||
-        (speed < smoothedSpeed * 10
-         && smoothedDiff < Constants.MAX_ACCELERATION * timeDifference);
-  }
-
-  /**
-   * Updates the grade measurements.
-   * 
-   * @param distance the distance the user just traveled
-   * @param elevationDifference the elevation difference between the current
-   *        reading and the previous reading
-   */
-  // @VisibleForTesting
-  void updateGrade(double distance, double elevationDifference) {
-    distanceBuffer.setNext(distance);
-    double smoothedDistance = distanceBuffer.getAverage();
-
-    // With the error in the altitude measurement it is dangerous to divide
-    // by anything less than 5.
-    if (!elevationBuffer.isFull() || !distanceBuffer.isFull()
-        || smoothedDistance < 5.0) {
+  public void resumeAt(long time) {
+    if (!paused) {
       return;
     }
-    currentGrade = elevationDifference / smoothedDistance;
-    gradeBuffer.setNext(currentGrade);
-    data.updateGradeExtremities(gradeBuffer.getAverage());
+
+    tripStatistics.setStartTime(time);
+    tripStatistics.setStopTime(-1L);
+    paused = false;
+    lastLocation = null;
+    lastMovingLocation = null;
+    speedBuffer.reset();
+    elevationBuffer.reset();
+    distanceBuffer.reset();
+    gradeBuffer.reset();
   }
 
   /**
-   * Pauses the track at the given time.
+   * Pauses the track at a given time.
    * 
    * @param time the time to pause at
    */
   public void pauseAt(long time) {
-    if (paused) { return; }
-
-    data.setStopTime(time);
-    data.setTotalTime(time - data.getStartTime());
-    lastLocation = null; // Make sure the counter restarts.
+    if (paused) {
+      return;
+    }
+    tripStatistics.setStopTime(time);
+    // TODO: total time needs to take into account pauses
+    tripStatistics.setTotalTime(time - tripStatistics.getStartTime());
     paused = true;
   }
 
   /**
-   * Resumes the current track at the given time.
-   *
-   * @param time the time to resume at
+   * Gets the trip statistics.
    */
-  public void resumeAt(long time) {
-    if (!paused) { return; }
-
-    // TODO: The times are bogus if the track is paused then resumed again
-    data.setStartTime(time);
-    data.setStopTime(-1);
-    paused = false;
-  }
-
-  @Override
-  public String toString() {
-    return "TripStatistics { Data: " + data.toString()
-         + "; Total Locations: " + totalLocations
-         + "; Paused: " + paused
-         + "; Current speed: " + currentSpeed
-         + "; Current grade: " + currentGrade
-         + "}";
+  public TripStatistics getTripStatistics() {
+    // Take a snapshot - we don't want anyone messing with our internals
+    return new TripStatistics(tripStatistics);
   }
 
   /**
-   * Returns the amount of time the user has been idle or 0 if they are moving.
+   * Returns the amount of time the user has been idle or 0 if he is moving.
    */
   public long getIdleTime() {
-    if (lastLocation == null || lastMovingLocation == null)
+    if (lastLocation == null || lastMovingLocation == null) {
       return 0;
+    }
     return lastLocation.getTime() - lastMovingLocation.getTime();
   }
 
   /**
-   * Gets the current elevation smoothed over several readings. The elevation
-   * data is very noisy so it is better to use the smoothed elevation than the
-   * raw elevation for many tasks.
-   * 
-   * @return The elevation smoothed over several readings
+   * Gets the smoothed elevation over several readings. The elevation readings
+   * is noisy so the smoothed elevation is better than the raw elevation for
+   * many tasks.
    */
   public double getSmoothedElevation() {
     return elevationBuffer.getAverage();
   }
 
-  public TripStatistics getStatistics() {
-    // Take a snapshot - we don't want anyone messing with our internals
-    return new TripStatistics(data);
+  /**
+   * Adds a location. This will update all of the internal variables with this
+   * new location.
+   * 
+   * @param location the location
+   * @param systemTime the system time for calculating totalTime. This should be
+   *          the phone's system time (not GPS time)
+   * @return true if the person is moving
+   */
+  public boolean addLocation(Location location, long systemTime) {
+    if (paused) {
+      Log.w(TAG, "Track is paused. Ignore addLocation.");
+      return false;
+    }
+
+    tripStatistics.setTotalTime(systemTime - tripStatistics.getStartTime());
+
+    double elevationDifference = updateElevation(location.getAltitude());
+    tripStatistics.updateLatitudeExtremities(location.getLatitude());
+    tripStatistics.updateLongitudeExtremities(location.getLongitude());
+
+    // If this is the first location, remember it and return.
+    if (lastLocation == null || lastMovingLocation == null) {
+      lastLocation = location;
+      lastMovingLocation = location;
+      return false;
+    }
+
+    // Don't do anything more if we didn't move since the last location.
+    double distance = lastLocation.distanceTo(location);
+    if (distance < minRecordingDistance && location.getSpeed() < Constants.MAX_NO_MOVEMENT_SPEED) {
+      lastLocation = location;
+      return false;
+    }
+
+    long timeDifference = location.getTime() - lastLocation.getTime();
+    if (timeDifference < 0) {
+      Log.e(TAG, "Negative time difference: " + timeDifference);
+      lastLocation = location;
+      return false;
+    }
+
+    tripStatistics.addTotalDistance(lastMovingLocation.distanceTo(location));
+    tripStatistics.addMovingTime(timeDifference);
+    updateSpeed(
+        location.getTime(), location.getSpeed(), lastLocation.getTime(), lastLocation.getSpeed());
+    updateGrade(distance, elevationDifference);
+    lastLocation = location;
+    lastMovingLocation = location;
+    return true;
   }
 
-  public void setMinRecordingDistance(int minRecordingDistance) {
-    this.minRecordingDistance = minRecordingDistance;
+  /**
+   * Updates a speed reading. Assumes the user is moving.
+   * 
+   * @param time the time
+   * @param speed the speed
+   * @param lastLocationTime the last location time
+   * @param lastLocationSpeed the last location speed
+   */
+  @VisibleForTesting
+  void updateSpeed(long time, double speed, long lastLocationTime, double lastLocationSpeed) {
+    if (!isValidSpeed(time, speed, lastLocationTime, lastLocationSpeed, speedBuffer)) {
+      Log.d(TAG, "Invalid speed. speed: " + speed + " lastLocationSpeed: " + lastLocationSpeed);
+      return;
+    }
+    speedBuffer.setNext(speed);
+    if (speed > tripStatistics.getMaxSpeed()) {
+      tripStatistics.setMaxSpeed(speed);
+    }
+    double movingSpeed = tripStatistics.getAverageMovingSpeed();
+    if (speedBuffer.isFull() && movingSpeed > tripStatistics.getMaxSpeed()) {
+      tripStatistics.setMaxSpeed(movingSpeed);
+    }
+  }
+
+  /**
+   * Updates an elevation reading.
+   * 
+   * @param elevation the elevation
+   */
+  @VisibleForTesting
+  double updateElevation(double elevation) {
+    double oldAverage = elevationBuffer.getAverage();
+    elevationBuffer.setNext(elevation);
+    double newAverage = elevationBuffer.getAverage();
+    tripStatistics.updateElevationExtremities(newAverage);
+    double elevationDifference = elevationBuffer.isFull() ? newAverage - oldAverage : 0.0;
+    if (elevationDifference > 0) {
+      tripStatistics.addTotalElevationGain(elevationDifference);
+    }
+    return elevationDifference;
+  }
+
+  /**
+   * Updates a grade reading.
+   * 
+   * @param distance the distance the user just traveled
+   * @param elevationDifference the elevation difference between the current
+   *          reading and the previous reading
+   */
+  @VisibleForTesting
+  void updateGrade(double distance, double elevationDifference) {
+    distanceBuffer.setNext(distance);
+    double smoothedDistance = distanceBuffer.getAverage();
+
+    /*
+     * With the error in the altitude measurement it is dangerous to divide by
+     * anything less than 5.
+     */
+    if (!elevationBuffer.isFull() || !distanceBuffer.isFull() || smoothedDistance < 5.0) {
+      return;
+    }
+    gradeBuffer.setNext(elevationDifference / smoothedDistance);
+    tripStatistics.updateGradeExtremities(gradeBuffer.getAverage());
+  }
+
+  /**
+   * Returns true if the speed is valid.
+   * 
+   * @param time the time
+   * @param speed the speed
+   * @param lastLocationTime the last location time
+   * @param lastLocationSpeed the last location speed
+   * @param speedBuffer a buffer of speed readings
+   */
+  public static boolean isValidSpeed(long time, double speed, long lastLocationTime,
+      double lastLocationSpeed, DoubleBuffer speedBuffer) {
+
+    /*
+     * There are a lot of noisy speed readings. Do the cheapest checks first,
+     * most expensive last.
+     */
+    if (speed == 0) {
+      return false;
+    }
+
+    /*
+     * The following code will ignore unlikely readings. 128 m/s seems to be an
+     * internal android error code.
+     */
+    if (Math.abs(speed - 128) < 1) {
+      return false;
+    }
+
+    /*
+     * See if the speed seems physically likely. Ignore any speeds that imply
+     * acceleration greater than 2g.
+     */
+    long timeDifference = time - lastLocationTime;
+    double speedDifference = Math.abs(lastLocationSpeed - speed);
+    if (speedDifference > Constants.MAX_ACCELERATION * timeDifference) {
+      return false;
+    }
+
+    /*
+     * Only check if the speed buffer is full. Check that the speed is less than
+     * 10X the smoothed average and the speed difference doesn't imply 2g
+     * acceleration.
+     */
+    if (!speedBuffer.isFull()) {
+      return true;
+    }
+    double average = speedBuffer.getAverage();
+    double diff = Math.abs(average - speed);
+    return (speed < average * 10) && (diff < Constants.MAX_ACCELERATION * timeDifference);
   }
 }