CODEWITHSUNDEEP
androidgeolocationlocationdistance
Usama Sarwar
Usama Sarwar

Reputation: 9020

Defining a threshold for Distance between two GEO Locations?

I am getting two GEO locations in my application and I have to calculate distance between them and after distance calculation I have to compare that result with the a defined threshold which is in my case 50 meters, how would I define that threshold in float. Also, Currently I my android fone is at the same location, but I always get the calculated distance between my 2 two geolocations determined after an interval to be more than 50 meters. How is it possible? I am taking threshold of 50 meters as:

private static final float DISTANCE_CHANGE_METERS = 50.0f; //50 meters

and I am calculating distance through following formula I found on StackOverflow:

public static float distFrom(double lat1, double lng1, double lat2, double lng2) {

    double earthRadius = 3958.75;
    double dLat = Math.toRadians(lat2 - lat1);
    double dLng = Math.toRadians(lng2 - lng1);
    double a = Math.sin(dLat / 2) * Math.sin(dLat / 2) + Math.cos(Math.toRadians(lat1)) * Math.cos(Math.toRadians(lat2)) * Math.sin(dLng / 2) * Math.sin(dLng / 2);
    double c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));
    double dist = earthRadius * c;

    int meterConversion = 1609;

    return new Float(dist * meterConversion).floatValue();
}

Kindly help me out in this regard. Thanks!

Upvotes: 0

Views: 1177

Answers (2)

Shobhit Puri
Shobhit Puri

Reputation: 26017

Currently my android phone is at the same location, but I always get the calculated distance between my 2 two geolocations determined after an interval to be more than 50 meters. How is that possible?

It actually depends on how you are passing the latitude and longitude to the distFrom function. Just to remind you that there is a simpler way to calculate the distance.
You can use just distanceTo() function in android API using Location to calculate the distance between two places like this:

Location locationA = new Location("point A");
locationA.setLatitude(latA); // co-ordinates in double
locationA.setLongitude(lngA);

Location locationB = new Location("point B");
locationB.setLatitude(latB);
locationB.setLongitude(lngB);

float distance = locationA.distanceTo(locationB);

If after using this also you are getting a distance greater than 50 meters then your co-ordinates that you are providing are not that accurate. Its perfectly fine because its tough to get accuracy with less that 50 meter precision. It would be most accurate if you are using internet along with GPS. If you see here, even if you use ACCURACY_HIGH as a criteria to choose a Location Provider, it provides accuracy of less than 100 meters. It can be accurate upto 100, 70 or even 50 meters. So even the most accurate option is not guaranteed to give extreme accuracy. If you are using GPS/Network provider for getting Location, then it your situation is very much possible. Getting location using `Network Provider1 is also not that accurate as it can catch signals of 2 network towers on different occasions, which can be well apart physically.

Hope it helps and clears the point to some extent. Its the problem to accuracy of your Location Provider.

Upvotes: 0

Paul Coghill
Paul Coghill

Reputation: 677

Could you just do:

if (distFrom(lat1,lng1,lat2,lng2) > DISTANCE_CHANGE_METERS)
{
    //greater than threshhold
}

Upvotes: 0

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