将GMSVisibleRegion转换为CLRegion或MKCoordinateRegion

Question

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);
}

Answer 1

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.

将其转换为a的一种方法CLRegion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.这可能不是该区域上最紧密的拟合圆,但由于圆不能适合视图的四边形,所以它可能足够接近.

这是一个辅助函数,用于计算两个CLLocationCoordinate值之间的距离(米):

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CLRegion可以像这样计算:

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"];

更新:

关于您的更新MKCoordinateRegion,您的示例代码可能无法正常工作.如果地图已经旋转了90度,然后farLeft和nearLeft将具有相同的纬度,并farRight与farLeft具有相同的经度,所以你的经度和纬度增量为零.

你会需要循环的所有四个farLeft,farRight,nearLeft,nearRight,计算每个的纬度和经度的最小值和最大值,然后从计算的增量.

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.它可以用以下内容初始化GMSVisibleRegion:

GMSMapView* mapView = ...;
....
GMSVisibleRegion visibleRegion = mapView.projection.visibleRegion;
GMSCoordinateBounds bounds = 
    [[GMSCoordinateBounds alloc] initWithRegion: visibleRegion];

在GMSCoordinateBounds于是具有northEast和southWest其限定的边界特性.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);

Answer 2

纯粹主义者的附录

如果你想要非常严格,那么你需要在国际日期线上进行修正.大多数应用程序都会浪费精力,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里

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)和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的特殊情况需要处理

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);

Answer 3

根据 @Saxon Druce 的回答，这是设置和获取region使用 MKCooperativeRegion 的快速扩展GMSMapView

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)
        }
    }
}