geolocation - How to Sort Geo-points according to the distance from current location in Android

Question

I have a "Place" object with a LatLng coordinate for each:

import com.google.android.gms.maps.model.LatLng;

public class Place{
    public String name;
    public LatLng latlng;

    public Restaurant(String name, LatLng latlng) {
        this.name = name;
        this.latlng = latlng;
    }
}

and I have an ArrayList of these Places, something like this:

    ArrayList<Place> places = new ArrayList<Place>();
    places.add("Place 1", LatLng(90.0,90.0));
    places.add("Place 2", LatLng(93.0,93.0));
    places.add("Place 3", LatLng(83.0,92.0));
    places.add("Place 4", LatLng(93.0,91.0));

and I have "my" LatLng:

    LatLng myLocation = new LatLng(10.0,10.0);

How can I sort these objects according to closest to me? Thanks for the help

Answer 1

Taking the algorithm from this answer from the question posted by @shieldstroy, that uses the Great Circle Distance, I got this example working.

Here is the Comparator:

public class SortPlaces implements Comparator<Place> {
    LatLng currentLoc;

    public SortPlaces(LatLng current){
        currentLoc = current;
    }
    @Override
    public int compare(final Place place1, final Place place2) {
        double lat1 = place1.latlng.latitude;
        double lon1 = place1.latlng.longitude;
        double lat2 = place2.latlng.latitude;
        double lon2 = place2.latlng.longitude;

        double distanceToPlace1 = distance(currentLoc.latitude, currentLoc.longitude, lat1, lon1);
        double distanceToPlace2 = distance(currentLoc.latitude, currentLoc.longitude, lat2, lon2);
        return (int) (distanceToPlace1 - distanceToPlace2);
    }

    public double distance(double fromLat, double fromLon, double toLat, double toLon) {
        double radius = 6378137;   // approximate Earth radius, *in meters*
        double deltaLat = toLat - fromLat;
        double deltaLon = toLon - fromLon;
        double angle = 2 * Math.asin( Math.sqrt(
                Math.pow(Math.sin(deltaLat/2), 2) +
                        Math.cos(fromLat) * Math.cos(toLat) *
                                Math.pow(Math.sin(deltaLon/2), 2) ) );
        return radius * angle;
    }
}

Here is the high level code, I just put this in onCreate():

        //My location, San Francisco
        double lat = 37.77657;
        double lng = -122.417506;
        LatLng latLng = new LatLng(lat, lng);

        //set up list
        ArrayList<Place> places = new ArrayList<Place>();

        places.add(new Place("New York", new LatLng(40.571256,73.98369)));
        places.add(new Place("Colorado", new LatLng(39.260658,-105.101615)));
        places.add(new Place("Los Angeles", new LatLng(33.986816,118.473819)));

        for (Place p: places){
            Log.i("Places before sorting", "Place: " + p.name);
        }

        //sort the list, give the Comparator the current location
        Collections.sort(places, new SortPlaces(latLng));

        for (Place p: places){
            Log.i("Places after sorting", "Place: " + p.name);
        }

Here is the log output:

04-17 23:04:16.074  12963-12963/com.maptest.daniel.maptest I/Places before sorting﹕ Place: New York
04-17 23:04:16.074  12963-12963/com.maptest.daniel.maptest I/Places before sorting﹕ Place: Colorado
04-17 23:04:16.074  12963-12963/com.maptest.daniel.maptest I/Places before sorting﹕ Place: Los Angeles
04-17 23:04:16.074  12963-12963/com.maptest.daniel.maptest I/Places after sorting﹕ Place: Los Angeles
04-17 23:04:16.074  12963-12963/com.maptest.daniel.maptest I/Places after sorting﹕ Place: Colorado
04-17 23:04:16.074  12963-12963/com.maptest.daniel.maptest I/Places after sorting﹕ Place: New York