My application server having thousands of users with their location(LatLng). I want nearest 50 users from any user's location to be displayed in app? How i can fast filter to get the nearest 50 users(LatLng) from server database?
I tried with Sort list of lon\lat points, start with nearest... but taking much time to sort and plot result on map. Please suggest.
First lets assume you have all the LatLng points into a list. (received by the database even if they are not sorted or somehow)
Use this function to calculate between LatLng's points.
public double CalculationByDistance(LatLng StartP, LatLng EndP) {
int Radius = 6371;// radius of earth in Km
double lat1 = StartP.latitude;
double lat2 = EndP.latitude;
double lon1 = StartP.longitude;
double lon2 = EndP.longitude;
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("####");
int kmInDec = Integer.valueOf(newFormat.format(km));
double meter = valueResult % 1000;
int meterInDec = Integer.valueOf(newFormat.format(meter));
return Radius * c;
}
StartP should be the user's LatLng.
EndP should be all the other LatLngs
You could create a list inserting all the distances between the user's LatLng and other's LatLng, after that sort that list. Now, you have a sorted list with the distances between the user's LatLng and the rest LatLngs, so with a for loop you could do whatever you want to. If it's taking time you could add a progress bar informing the user that something is happening/loading etc.
