Get the max latitude and longitude given radius (meters) and position

Question

I need help with my code. I want to obtain the max latitude and the max longitude (in degrees) given a radius in meters and the actual position in latitude and longitude (in degrees). Can someone help me?

Thanks!!

Answer 1

First, every degree of latitude contains appx 111.1 km, so it's easy to recalculate linear delta to latitude delta.

Second, linear appearance of 1 longitude degree is different and depends on latitude: small close to poles, large close to equator. Approximate equation is the following:

kmInLongitudeDegree = 111.320 * Math.cos( latitude / 180.0 * Math.PI)

Combining this, it's easy to get deltas of latitude and longitude that will cover your circle:

deltaLat = radiusInKm / 111.1;
deltaLong = radiusInKm / kmInLongitudeDegree;

minLat = lat - deltaLat;  
maxLat = lat + deltaLat;
minLong = long - deltaLong; 
maxLong = long + deltaLong;

For more precise calculation, look here: http://en.wikipedia.org/wiki/Longitude (section Length of a degree of longitude).

On Android, to obtain how many meters one latitude degree contains, make 2 Location objects: one with current coordinates, and one with latitude shifted on 0.1 degree, then calculate distance between them and multiply by 10. The same with longitude.