Geo points in area - ios

Question

I am working on iOS app where at some point I want to get user's location and present her all point of interests on map that are inside a circular area where centre of this area is user's current location and radius is constant. Points of interests are stored in database with their coordinates (latitude, longitude).
I have already managed to get user's location. Now I am trying to figure out how to calculate if certain coordinates are in that area.
I was thinking that I can calculate distance of some point from centre using this equation:
d = sqrt((centre_latitude - point_latitude)^2 + (centre_longitude - point_longitude)^2)
Where d is distance of that point from circle centre. Then I could simply compare d with radius.
I am not sure if this is right and also efficient approach. I can imagine that if I have thousands of points this would be really slow (query database for each point then do the math).

Answer 1

You can try this:
-(void)locationManager:(CLLocationManager *)manager didUpdateLocations:(NSArray *)locations {
float lon= // longitude you want to compare to your current postion
float lat=//your latitude you want to compare to your current position
float rad=//radius , if you give this 100m, then it checks the given points are within the 100m from you are not
CLLocation *centerLocation = [[CLLocation alloc] initWithLatitude:lat
longitude:lon];
CLLocation *lastLocation=[locations lastObject];
//display current lat and lon in text fields
currentLat.text=[NSString stringWithFormat:#"%f",lastLocation.coordinate.latitude];
currentLon.text=[NSString stringWithFormat:#"%f",lastLocation.coordinate.longitude];
CLLocationDistance distance = [lastLocation distanceFromLocation:centerLocation];
if (distance<=rad) {
// you are within the radius
}
CLLocationAccuracy accuracy = [lastLocation horizontalAccuracy];
if(accuracy <=10) { //accuracy in metres
[manager stopUpdatingLocation];
}
}

Answer 2

You can use Haversine formula.
I have it implemented in Java for Android, maybe it helps you.
private static double calculateDistanceInMiles(Location StartP, Location EndP) {
//Haversine formula
//double Radius=6371; // to get distance in kms
double Radius=3963.1676; //to get distance in miles
double lat1 = StartP.getLatitude();
double lat2 = EndP.getLatitude();
double lon1 = StartP.getLongitude();
double lon2 = EndP.getLongitude();
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));
return Radius * c;
}