我正在使用GoogleMaps SDK，目前我正在尝试将GMSVisibleRegion转换为CLRegion。
GMSVisibleRegion定义为：
typedef struct {
CLLocationCoordinate2D nearLeft;
CLLocationCoordinate2D nearRight;
CLLocationCoordinate2D farLeft;
CLLocationCoordinate2D farRight;
} GMSVisibleRegion;
最快的方法是什么？
不幸的是，很难理解开发人员在命名“near”和“far”时的含义。我认为这个评论也很有用：
/**
* Returns the region (four location coordinates) that is visible according to
* the projection.
*
* The visible region can be non-rectangular. The result is undefined if the
* projection includes points that do not map to anywhere on the map (e.g.,
* camera sees outer space).
*/
- (GMSVisibleRegion)visibleRegion;
非常感谢！
编辑： 好的，我的第一步是创建一个GMSVisibleRegion的MKCoordinateRegion。
我建议使用以下代码将GMSVisibleRegion转换为MKCoordinateRegion。任何异议。
+ (MKCoordinateRegion)regionForCenter:(CLLocationCoordinate2D)center andGMSVisibleRegion:(GMSVisibleRegion)visibleRegion
{
CLLocationDegrees latitudeDelta = visibleRegion.farLeft.latitude - visibleRegion.nearLeft.latitude;
CLLocationDegrees longitudeDelta = visibleRegion.farRight.longitude - visibleRegion.farLeft.longitude;
MKCoordinateSpan span = MKCoordinateSpanMake(latitudeDelta, longitudeDelta);
return MKCoordinateRegionMake(center, span);
}
答案 0 :(得分：11)
我的猜测是“靠近”是屏幕底部视图的角落，“远”是指屏幕顶部的角落。这是因为如果您倾斜视图，则底角最靠近相机，顶角距离相机最远。
将此转换为CLRegion的一种方法可能是使用相机的目标作为中心，然后计算从最大距离到四个角的半径。这可能不是该区域最紧密的拟合圆，但由于圆不能适合视图的四边形，它可能足够接近。
这是一个辅助函数，用于计算两个CLLocationCoordinate值之间的距离：
double getDistanceMetresBetweenLocationCoordinates(
CLLocationCoordinate2D coord1,
CLLocationCoordinate2D coord2)
{
CLLocation* location1 =
[[CLLocation alloc]
initWithLatitude: coord1.latitude
longitude: coord1.longitude];
CLLocation* location2 =
[[CLLocation alloc]
initWithLatitude: coord2.latitude
longitude: coord2.longitude];
return [location1 distanceFromLocation: location2];
}
然后可以像这样计算CLRegion：
GMSMapView* mapView = ...;
...
CLLocationCoordinate2D centre = mapView.camera.target;
GMSVisibleRegion* visibleRegion = mapView.projection.visibleRegion;
double nearLeftDistanceMetres =
getDistanceMetresBetweenLocationCoordinates(centre, visibleRegion.nearLeft);
double nearRightDistanceMetres =
getDistanceMetresBetweenLocationCoordinates(centre, visibleRegion.nearRight);
double farLeftDistanceMetres =
getDistanceMetresBetweenLocationCoordinates(centre, visibleRegion.farLeft);
double farRightDistanceMetres =
getDistanceMetresBetweenLocationCoordinates(centre, visibleRegion.farRight);
double radiusMetres =
MAX(nearLeftDistanceMetres,
MAX(nearRightDistanceMetres,
MAX(farLeftDistanceMetres, farRightDistanceMetres)));
CLRegion region = [[CLRegion alloc]
initCircularRegionWithCenter: centre radius: radius identifier: @"id"];
<强>更新
关于MKCoordinateRegion的更新，您的示例代码可能无效。如果地图已旋转90度，则farLeft和nearLeft将具有相同的纬度，farRight和farLeft将具有相同的经度，因此您的纬度和经度三角洲将为零。
您需要遍历farLeft，farRight，nearLeft，nearRight的所有四个，计算每个的经度和经度的最小值和最大值，然后从中计算增量。
适用于iOS的Google Maps SDK包含一个帮助程序类，已经为您完成了一些帮助 - GMSCoordinateBounds。它可以使用GMSVisibleRegion：
GMSMapView* mapView = ...;
....
GMSVisibleRegion visibleRegion = mapView.projection.visibleRegion;
GMSCoordinateBounds bounds =
[[GMSCoordinateBounds alloc] initWithRegion: visibleRegion];
然后GMSCoordinateBounds具有northEast和southWest属性，用于定义边界。所以你可以按如下方式计算增量：
CLLocationDegrees latitudeDelta =
bounds.northEast.latitude - bounds.southWest.latitude;
CLLocationDegrees longitudeDelta =
bounds.northEast.longitude - bounds.southWest.longitude;
您还可以从边界计算中心，因此MKCoordinateRegion：
CLLocationCoordinate2D centre = CLLocationCoordinate2DMake(
(bounds.southWest.latitude + bounds.northEast.latitude) / 2,
(bounds.southWest.longitude + bounds.northEast.longitude) / 2);
MKCoordinateSpan span = MKCoordinateSpanMake(latitudeDelta, longitudeDelta);
return MKCoordinateRegionMake(centre, span);
答案 1 :(得分：8)
纯粹主义者的附录
如果你想要绝对严谨，你需要在国际日期线上做出修正。这在大多数应用程序中都是浪费精力，但这个问题一直让我感到非常悲痛，所以我想把它扔进社区帽子
以Druce的更新为基础（害怕我无法发表评论）......
GMSMapView* mapView = ...;
....
GMSVisibleRegion visibleRegion = mapView.projection.visibleRegion;
GMSCoordinateBounds bounds =
[[GMSCoordinateBounds alloc] initWithRegion: visibleRegion];
纬度不需要做任何事情
CLLocationDegrees latitudeDelta =
bounds.northEast.latitude - bounds.southWest.latitude;
该交易涉及跨越国际日期线的地区可能在日本的西南角（经度+140）及其在阿拉斯加的东北角（经度-150）。加起来除以2可以得出全球错误的一面。
northEast.longitude小于southWest.longitude需要处理的特殊情况
CLLocationCoordinate2D centre;
CLLocationDegrees longitudeDelta;
if(bounds.northEast.longitude >= bounds.southWest.longitude) {
//Standard case
centre = CLLocationCoordinate2DMake(
(bounds.southWest.latitude + bounds.northEast.latitude) / 2,
(bounds.southWest.longitude + bounds.northEast.longitude) / 2);
longitudeDelta = bounds.northEast.longitude - bounds.southWest.longitude;
} else {
//Region spans the international dateline
centre = CLLocationCoordinate2DMake(
(bounds.southWest.latitude + bounds.northEast.latitude) / 2,
(bounds.southWest.longitude + bounds.northEast.longitude + 360) / 2);
longitudeDelta = bounds.northEast.longitude + 360
- bounds.southWest.longitude;
}
MKCoordinateSpan span = MKCoordinateSpanMake(latitudeDelta, longitudeDelta);
return MKCoordinateRegionMake(centre, span);
答案 2 :(得分：4)
对于根据目前提供的所有答案和更正寻找样板代码的任何人，这里的region作为GMSMapView上的类别实现：
//
// GMSMapViewExtensions.h
//
#import <Foundation/Foundation.h>
#import <MapKit/MapKit.h>
#import <GoogleMaps/GoogleMaps.h>
@interface GMSMapView (GMSMapViewExtensions)
@end
和
//
// GMSMapViewExtensions.m
//
#import "GMSMapViewExtensions.h"
@implementation GMSMapView (GMSMapViewExtensions)
- (MKCoordinateRegion) region {
GMSVisibleRegion visibleRegion = self.projection.visibleRegion;
GMSCoordinateBounds * bounds = [[GMSCoordinateBounds alloc] initWithRegion: visibleRegion];
CLLocationDegrees latitudeDelta = bounds.northEast.latitude - bounds.southWest.latitude;
CLLocationCoordinate2D centre;
CLLocationDegrees longitudeDelta;
if (bounds.northEast.longitude >= bounds.southWest.longitude) {
// Standard case
centre = CLLocationCoordinate2DMake(
(bounds.southWest.latitude + bounds.northEast.latitude) / 2,
(bounds.southWest.longitude + bounds.northEast.longitude) / 2);
longitudeDelta = bounds.northEast.longitude - bounds.southWest.longitude;
} else {
// Region spans the international dateline
centre = CLLocationCoordinate2DMake(
(bounds.southWest.latitude + bounds.northEast.latitude) / 2,
(bounds.southWest.longitude + bounds.northEast.longitude + 360) / 2);
longitudeDelta = bounds.northEast.longitude + 360 - bounds.southWest.longitude;
}
MKCoordinateSpan span = MKCoordinateSpanMake(latitudeDelta, longitudeDelta);
return MKCoordinateRegionMake(centre, span);
}
- (MKMapRect)visibleMapRect {
MKCoordinateRegion region = [self region];
MKMapPoint a = MKMapPointForCoordinate(CLLocationCoordinate2DMake(
region.center.latitude + region.span.latitudeDelta / 2,
region.center.longitude - region.span.longitudeDelta / 2));
MKMapPoint b = MKMapPointForCoordinate(CLLocationCoordinate2DMake(
region.center.latitude - region.span.latitudeDelta / 2,
region.center.longitude + region.span.longitudeDelta / 2));
return MKMapRectMake(MIN(a.x, b.x), MIN(a.y, b.y), ABS(a.x - b.x), ABS(a.y - b.y));
}
@end
用法示例：
GMSMapView * mapView = .... // init code
MKCoordinateRegion mapRegion = mapView.region;
答案 3 :(得分：3)
根据@Saxon Druce的答案，这是使用region上的MKCoordinateRegion设置和获取GMSMapView的快速扩展
extension GMSMapView {
var region : MKCoordinateRegion {
get {
let position = self.camera
let visibleRegion = self.projection.visibleRegion()
let bounds = GMSCoordinateBounds(region: visibleRegion)
let latitudeDelta = bounds.northEast.latitude - bounds.southWest.latitude
let longitudeDelta = bounds.northEast.longitude - bounds.southWest.longitude
let center = CLLocationCoordinate2DMake(
(bounds.southWest.latitude + bounds.northEast.latitude) / 2,
(bounds.southWest.longitude + bounds.northEast.longitude) / 2)
let span = MKCoordinateSpanMake(latitudeDelta, longitudeDelta)
return MKCoordinateRegionMake(center, span)
}
set {
let northEast = CLLocationCoordinate2DMake(newValue.center.latitude - newValue.span.latitudeDelta/2, newValue.center.longitude - newValue.span.longitudeDelta/2)
let southWest = CLLocationCoordinate2DMake(newValue.center.latitude + newValue.span.latitudeDelta/2, newValue.center.longitude + newValue.span.longitudeDelta/2)
let bounds = GMSCoordinateBounds(coordinate: northEast, coordinate: southWest)
let update = GMSCameraUpdate.fitBounds(bounds, withPadding: 0)
self.moveCamera(update)
}
}
}