缩放MapView以显示第180个子午线的注释

Question

我有一个带有< 5注解的MapView。加载地图时，我想放大以在这些注释上居中放置地图，如this。但是，当注释分布在第180个子午线（经度从-180到+180）时，链接方法不起作用。即使它们聚集在主要子午线周围，我如何可靠地放大注释？

例如，如果我有X（0179）和y（0，-179），那么我愿意与两个度经度的宽度，而不是358。

Answer 1

MapKit含矩形为iOS实际上具有在一个的MKMapView内置的功能，做到这一点：

showAnnotations(annotations: [MKAnnotation], animated: Bool) 

但是，此功能不会提供超过缩放级别的控制，所以我仍然不得不使自己的功能。这里是伪代码：

zoomToAnnotations(annotations, zoomLimit) { 
    // calculate the midpoint as the average latitude and longitude 
    average_latitude = mean(a.coordinate.latitude for a in annotations) 
    average_longitude = atan2(mean(sin(a.coordinate.longitude) for a in annotations), mean(cos(a.coordinate.longitude) for a in annotations)) // be careful with degrees and radians in real code 
    regular_midpoint = coordinate(average_latitude, average_longitude) 
    // subtract 180 from longitude for the midpoint of the region crossing the meridian 
    meridian_midpoint = coordinate(average_latitude, average_longitude - 180.0) 
    if (meridian_midpoint.longitude < -180) { 
     meridian_midpoint.longitude += 360.0 
    } 

    // work out which region will be smaller and center map there 
    meridian_sum = sum(a.coordinate.distance(meridian_midpoint) for a in annotations) 
    regular_sum = sum(a.coordinate.distance(regular_midpoint) for a in annotations) 
    regular_max_distance = max(a.coordinate.distance(regular_midpoint) for a in annotations) 
    if meridian_sum < regular_sum { 
     meridian_max_distance = max(a.coordinate.distance(meridian_midpoint) for a in annotations) 
     centerMapWithRadius(meridian_midpoint, max(zoomLimit, meridian_max_distance)) 
    } else { 
     regular_max_distance = max(a.coordinate.distance(regular_midpoint) for a in annotations) 
     centerMapWithRadius(regular_midpoint, max(zoomLimit, regular_max_distance)) 
    } 
} 

这种方法是不完美的，因为它的点，而不是具有最远点从边缘的距离相等的均值中心。