How to get residence time in a geofence? - geolocation

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