Check if a latitude and longitude is within a circle

Question

See this illustration:

What I would like to know is:

1. How to create an area (circle) when given a latitude and longitude and the distance (10 kilometers)
2. How to check (calculate) if a latitude and longitude is either inside or outside the area

I would prefer if you can give me code example in Java or specifically for Android with Google Maps API V2

Answer 1

What you basically need, is the distance between two points on the map:

float[] results = new float[1]; Location.distanceBetween(centerLatitude, centerLongitude, testLatitude, testLongitude, results); float distanceInMeters = results[0]; boolean isWithin10km = distanceInMeters < 10000; 

If you have already Location objects:

Location center; Location test; float distanceInMeters = center.distanceTo(test); boolean isWithin10km = distanceInMeters < 10000; 

Here is the interesting part of the API used: https://developer.android.com/reference/android/location/Location.html

Answer 2

Check this:

 private boolean isMarkerOutsideCircle(LatLng centerLatLng, LatLng draggedLatLng, double radius) {     float[] distances = new float[1];     Location.distanceBetween(centerLatLng.latitude,             centerLatLng.longitude,             draggedLatLng.latitude,             draggedLatLng.longitude, distances);     return radius < distances[0]; }