How to sort geo-points according to distance from current location in Android
I have a "Place" object with 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 the one closest to me? thanks for the help
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Taking the algorithm from this answer from the question posted by @shieldstroy that uses Great Circle Distance , I got this example.
Here is 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 it 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
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Once you've got your current location, you can sort by calculating the distance (most suitable for places like restaurants) like this:
-
Calculate the distance to each object
http://maps.googleapis.com/maps/api/directions/json?origin="+yourLat+","+yourLong+"&destination="+toLat+","+toLong+"&sensor=false&mode=DRIVING
-
After calculating each distance, apply some simple sorting algorithm for those distances.
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There are various methods available for calculating the distance. Quite simple - Haversine's Formula ( http://rosettacode.org/wiki/Haversine_formula#Java ). A more accurate calculation would be the Vincenti Formula. If the two locations are not far away, Haversine's solution is sufficient.
After calculating the distance, you simply sort the array using a comparator, for example:
Collections.sort(places, new Comparator<Place>() {
public int compare(Place p1, Place p2) {
return Double.compare(p1.getDistance(), p2.getDistance());
}
});
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