Algorithm for Creating user Defined Geofences

Question

I've got a latitude & longitude of a point. I want all the readings of latitude & longitude within a radius of 500M with respect to that given point. Is any method for that? Is it possible? Is there any algorithm for it?

Answer 1

There are many formulas available to calculate the distance between two lat/long points (it won't be exact due to altitude variation, but very close), and filter your sample points based on distance from your given point.

A nice overview of what's available (with math and source code) is available here: http://www.movable-type.co.uk/scripts/latlong.html

Browse through there and pick the distance formula that fits your needs the best.

Answer 2

Here's a solution on StackOverflow for finding the distance between 2 locations, by Usman Kurd

https://stackoverflow.com/a/14394403/2128327

So with a little tweak, we can use his function:

  public double getKmDistance(GeoPoint StartP, GeoPoint EndP) {
    int Radius=6371;//radius of earth in Km         
    double lat1 = StartP.getLatitudeE6()/1E6;
    double lat2 = EndP.getLatitudeE6()/1E6;
    double lon1 = StartP.getLongitudeE6()/1E6;
    double lon2 = EndP.getLongitudeE6()/1E6;
    double dLat = Math.toRadians(lat2-lat1);
    double dLon = Math.toRadians(lon2-lon1);
    double a = Math.sin(dLat/2) * Math.sin(dLat/2) +
    Math.cos(Math.toRadians(lat1)) * Math.cos(Math.toRadians(lat2)) *
    Math.sin(dLon/2) * Math.sin(dLon/2);
    double c = 2 * Math.asin(Math.sqrt(a));
    double valueResult= Radius*c;
    double km=valueResult/1;
    DecimalFormat newFormat = new DecimalFormat("####");
    kmInDec =  Integer.valueOf(newFormat.format(km));
    meter=valueResult%1000;
    meterInDec= Integer.valueOf(newFormat.format(meter));
    Log.i("Radius Value",""+valueResult+"   KM  "+kmInDec+" Meter   "+meterInDec);

    return kmInDec;
 }

then let's say that you have a list of locations:

ArrayList<GeoPoint> geoPoints = new ArrayList<GeoPoint>();

And we have our current location:

GeoPoint currentLocation = new GeoPoint(..);

then you can do this:

ArrayList<GeoPoint> within500Km = new ArrayList<GeoPoint>();

for (GeoPoint g : geoPoints)
    if (getKmDistance(currentLocation, g) <= 500.0)
        within500Km.add(g);

for(GeoPoint g : within500Km)
    System.out.println("> "+g.getLatitudeE6()+" : "+g.getLongitudeE6()+" ");