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.