今天用到百度地图获取屏幕范围内的经纬度，在此记录一下。
// 当前屏幕中心点的经纬度
double centerLongitude = self.mapView.region.center.longitude;
double centerLatitude = self.mapView.region.center.latitude;
//当前屏幕显示范围的经纬度
CLLocationDegrees pointssLongitudeDelta = self.mapView.region.span.longitudeDelta;
CLLocationDegrees pointssLatitudeDelta = self.mapView.region.span.latitudeDelta;
//左上角
double leftUpLong = centerLongitude - pointssLongitudeDelta/2.0;
double leftUpLati = centerLatitude - pointssLatitudeDelta/2.0;
//右上角
double rightUpLong = centerLongitude + pointssLongitudeDelta/2.0;
double rightUpLati = centerLatitude - pointssLatitudeDelta/2.0;
//左下角
double leftDownLong = centerLongitude - pointssLongitudeDelta/2.0;
double leftDownlati = centerLatitude + pointssLatitudeDelta/2.0;
//右下角
double rightDownLong = centerLongitude + pointssLongitudeDelta/2.0;
double rightDownLati = centerLatitude + pointssLatitudeDelta/2.0;
NSLog(@"\n 左上 %f,%f---------\n 右上 %f,%f-------\n 左下 %f,%f----- \n 右下 %f,%f",leftUpLong,leftUpLati,rightUpLong,rightUpLati,leftDownLong,leftDownlati,rightDownLong,rightDownLati);
