code: public GeoRect getBoundingBox() {
          double radDist = radius / EARTH_RADIUS;
          double radLat = Math.toRadians(latitude);
          double radLon = Math.toRadians(longitude);
  
          double minLat = radLat - radDist;
          double maxLat = radLat + radDist;
  
          double minLon, maxLon;
          if (minLat > MIN_LAT && maxLat < MAX_LAT) {
              double deltaLon = Math.asin(Math.sin(radDist) /
                  Math.cos(radLat));
              minLon = radLon - deltaLon;
              if (minLon < MIN_LON) {
                  minLon += 2d * Math.PI;
              }
              maxLon = radLon + deltaLon;
              if (maxLon > MAX_LON) {
                  maxLon -= 2d * Math.PI;
              }
          } else {
              // a pole is within the distance
              minLat = Math.max(minLat, MIN_LAT);
              maxLat = Math.min(maxLat, MAX_LAT);
              minLon = MIN_LON;
              maxLon = MAX_LON;
          }
  
          return new GeoRect(
              new GeoPoint(Math.toDegrees(maxLat), Math.toDegrees(minLon)),
              new GeoPoint(Math.toDegrees(minLat), Math.toDegrees(maxLon))
          );
      }
docs: see http://janmatuschek.de/LatitudeLongitudeBoundingCoordinates