ios - 无法绘制跨越经度 +/-180 的 MKPolylineView

Question

我在 MKMapView 上绘制 MKPolylineView 时遇到问题。这条线代表一次环游世界的旅行，起点和终点都在纽约附近，总是向东行驶。从日本到旧金山的行程中有一段横跨太平洋，因此经度为 +/-180。 MKPolylineView 确实连接了这两点，但它的移动方向错误。也就是说，这条线路从日本向西返回旧金山，而不是向东穿越太平洋。我没有看到任何选项可以让我指定线段应该沿着哪个方向连接两点。

简单来说，MKMapView 似乎不明白地球是圆的。有没有一种方法可以让我按预期画线，从日本向东行驶到旧金山？

我有一张截图可以清楚地显示问题:
The Polyline http://www.builtlight.org/pub/MKPolylineView.png

Answer 1

这似乎是 MKMapView 的一个限制。

解决方法是将 +/-180 交叉点拆分为“东”和“西”部分。

对于环球旅行(完成 == 开始)，您可以将十字路口的“西”部分放在折线的前面。
例如:

CLLocationCoordinate2D newYorkCoord = CLLocationCoordinate2DMake(40.7141667, -74.0063889);
CLLocationCoordinate2D londonCoord = CLLocationCoordinate2DMake(51.5, -0.116667);
CLLocationCoordinate2D japanCoord = CLLocationCoordinate2DMake(36, 138);
CLLocationCoordinate2D sanFranciscoCoord = CLLocationCoordinate2DMake(37.775, -122.4183333);

CLLocationCoordinate2D japanToSFMidpointEast;
//use average calc as crude way to find midpoint...
japanToSFMidpointEast.latitude = (japanCoord.latitude + sanFranciscoCoord.latitude)/2.0;
japanToSFMidpointEast.longitude = 180;

CLLocationCoordinate2D japanToSFMidpointWest;
japanToSFMidpointWest.latitude = japanToSFMidpointEast.latitude;
japanToSFMidpointWest.longitude = -180;

int pointsCount = 6;
CLLocationCoordinate2D *points = malloc(pointsCount * sizeof(CLLocationCoordinate2D));
points[0] = japanToSFMidpointWest;
points[1] = sanFranciscoCoord;
points[2] = newYorkCoord;
points[3] = londonCoord;
points[4] = japanCoord;
points[5] = japanToSFMidpointEast;
MKPolyline *polyline = [MKPolyline polylineWithCoordinates:points count:pointsCount];
[mapView addOverlay:polyline];
free(points);
points = NULL;

如果旅行不是环游世界(完成!=开始)，则必须使用两条折线。
此示例从日本到 SF:

CLLocationCoordinate2D japanCoord = CLLocationCoordinate2DMake(36, 138);
CLLocationCoordinate2D sanFranciscoCoord = CLLocationCoordinate2DMake(37.775, -122.4183333);

CLLocationCoordinate2D japanToSFMidpointEast;
japanToSFMidpointEast.latitude = (japanCoord.latitude + sanFranciscoCoord.latitude)/2.0;
japanToSFMidpointEast.longitude = 180;

CLLocationCoordinate2D japanToSFMidpointWest;
japanToSFMidpointWest.latitude = japanToSFMidpointEast.latitude;
japanToSFMidpointWest.longitude = -180;

int eastPointsCount = 2;
CLLocationCoordinate2D *eastPoints = malloc(eastPointsCount * sizeof(CLLocationCoordinate2D));
eastPoints[0] = japanCoord;
eastPoints[1] = japanToSFMidpointEast;
MKPolyline *eastPolyline = [MKPolyline polylineWithCoordinates:eastPoints count:eastPointsCount];
[mapView addOverlay:eastPolyline];
free(eastPoints);
eastPoints = NULL;

int westPointsCount = 2;
CLLocationCoordinate2D *westPoints = malloc(westPointsCount * sizeof(CLLocationCoordinate2D));
westPoints[0] = japanToSFMidpointWest;
westPoints[1] = sanFranciscoCoord;
MKPolyline *westPolyline = [MKPolyline polylineWithCoordinates:westPoints count:westPointsCount];
[mapView addOverlay:westPolyline];
free(westPoints);
westPoints = NULL;