Question

我有一个带有＆lt; 5注释的MapView。加载地图时，我想放大这些注释的地图中心，例如this。但是，当注释分布在第180个子午线（经度从-180到-180）时，链接的方法不起作用。即使它们聚集在本初子午线周围，我如何才能稳健地缩放注释？

例如，如果我有x（0,179）和y（0，-179），那么我想要一个宽度为2度经度的包含矩形，而不是358。

Answer 1

MapKit for iOS实际上在MKMapView中有一个内置函数，它执行此操作：

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

但是，此功能无法控制缩放级别，因此我仍然需要自己创建功能。这是伪代码：

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))
    }
}

这种方法并不完美，因为它以点的平均值为中心，而不是使最远点与边缘的距离相等。

缩放MapView以显示第180个子午线的注释

1 个答案: