How to get residence time in a geofence?

Question

Simple question need simple answer. How can I track the residence time in a specific geofence. When I add geofence with Trigger on Enter, will I automatic receive a trigger when I leave that geofence. Basically I need to remember the time when I enter a geofence and when I leave that geofence so I can subtract leave-enter time and have my duration time. But I believe its not that easy to do that. So any other idea or advise how to solve that problem efficient ? Thanks

Answer 1

I found one solution for this problem. In order to determine the dwell time in a geofence i have to get the time when user trigger a geofence and then i use to calculate if user leave the geofence with this mathematical method

 Handler handler = new Handler();
    getCurrentLatLng();
    final Runnable myRunnable = new Runnable() {
        public void run() {
            GeofenceFinished myFinishedGeofence = db.getGeofenceFinishedByID("Finished" + id);
            if (!isUserInRegion(latitude, longitude, myLatLng.latitude, myLatLng.longitude, rd)
                    || myFinishedGeofence == null) {
                String time = convertTime(endTime - startTime);
                // get the finishedGeofence and set the duration of stay time
                if (myFinishedGeofence != null)
                    setDurationOfStay("Finished" + id, time, getCurrentTime(System.currentTimeMillis()));
                Toast.makeText(mContext, "Finish to determine duration of stay of " + myFinishedGeofence.getAddress(), Toast.LENGTH_SHORT).show();
                handler.removeCallbacks(this);
            } else {
                getCurrentLatLng();
                endTime += Constants.DELAY;
                handler.postDelayed(this, Constants.DELAY);
            }
        }

        private void setDurationOfStay(String geofenceid, String time, String endTime) {
            if (db == null) db = GeofenceDatabaseHelper.getInstance(mContext);
            if (!db.setDurationOfFinishedGeofence(geofenceid, time, endTime)) {
                Log.i("setDurationOfStay", "fail");
            }
        }
    };
    handler.postDelayed(myRunnable, Constants.DELAY);

private boolean isUserInRegion(double firstLat, double firstLog, double curLat, double curLog, float radius) {
    double distance = calculateDistance(firstLat, firstLog, curLat, curLog);
    return distance <= radius;
}

To calculate the distance of user and center of geofence, i need to convert the current latitude and longitude in meter, so i can calculate that with the parametic equation for circle

So I use this approach from github

    // https://github.com/mgavaghan/geodesy
private double calculateDistance(double firstLat, double firstLog, double curLat, double curLog) {
    GeodeticCalculator geoCalc = new GeodeticCalculator();
    Ellipsoid reference = Ellipsoid.WGS84;
    GlobalPosition pointA = new GlobalPosition(firstLat, firstLog, 0.0); // Point A
    GlobalPosition userPos = new GlobalPosition(curLat, curLog, 0.0); // Point B
    // Distance between Point A and Point B
    double distance = geoCalc.calculateGeodeticCurve(reference, userPos, pointA).getEllipsoidalDistance();
    return distance;
}

hope it helps someone :D