在MKMapView上绘制Great Circle叠加线

Question

我正在尝试在MKMapView上的两个纬度/经度点之间绘制一条Great Circle线.这是一条看起来呈圆形的线(地球上的"直线"),最好在这里可视化.事实上,这个非常奇怪的WordPress网站似乎开始准确地描述如何做到这一点,但它在最初的几个步骤之后突然结束.

阅读Apple的文档,我看到了

在iOS 4.0及更高版本中,您还可以使用投影贴图坐标而不是区域来指定某些值.当您将地球的曲面投影到平面上时,您会得到一个二维版本的地图,其中经度线看起来是平行的.使用MKMapPoint,MKMapSize和MKMapRect数据类型指定此地图上的位置和距离.您可以使用这些数据类型指定地图的可见区域以及指定叠加的位置.

我如何将它应用于Great Circle叠加我不确定.有人可以帮忙吗？

Answer 1

我已经实现了这个目的,为使用MKPolyline的两个机场之间的飞机绘制一条很棒的航线.

+ (void)createGreatCircleMKPolylineFromPoint:(CLLocationCoordinate2D)point1 
                                     toPoint:(CLLocationCoordinate2D)point2
                                  forMapView:(MKMapView*)mapView
{
double lat1 = point1.latitude;
double lon1 = point1.longitude;
double lat2 = point2.latitude;
double lon2 = point2.longitude;
lat1 = lat1 * (PI/180);
lon1 = lon1 * (PI/180);
lat2 = lat2 * (PI/180);
lon2 = lon2 * (PI/180);
double d = 2 * asin( sqrt(pow(( sin( (lat1-lat2)/2) ), 2) + cos(lat1) * cos(lat2) * pow(( sin( (lon1-lon2)/2) ), 2)));
int numsegs = 100;
CLLocationCoordinate2D *coords = malloc(sizeof(CLLocationCoordinate2D) * numsegs);
double f = 0.0;
for(int i=1; i<=numsegs; i++)
{
    f += 1.0 / (float)numsegs;
    double A=sin((1-f)*d)/sin(d);
    double B=sin(f*d)/sin(d);
    double x = A*cos(lat1) * cos(lon1) +  B * cos(lat2) * cos(lon2);
    double y = A*cos(lat1) * sin(lon1) +  B * cos(lat2) * sin(lon2);
    double z = A*sin(lat1)           +  B*sin(lat2);
    double latr=atan2(z, sqrt(pow(x, 2) + pow(y, 2) ));
    double lonr=atan2(y, x);
    double lat = latr * (180/PI);
    double lon = lonr * (180/PI);
    //        NSLog(@"lat: %f lon: %f", lat, lon);
    CLLocationCoordinate2D loc = CLLocationCoordinate2DMake(lat, lon);
    coords[i - 1] = loc;
}

//check for circling west to east. If the plane is crossing 180, we need
//to draw two lines or else the polyline connects the dots and draws a straight
//line all the way across the map.
CLLocationCoordinate2D prevCoord;
BOOL twoLines = NO;
int numsegs2 = 0;
CLLocationCoordinate2D *coords2;

for(int i=0; i<numsegs; i++)
{
    CLLocationCoordinate2D coord = coords[i];
    if(prevCoord.longitude < -170 && prevCoord.longitude > -180  && prevCoord.longitude < 0 
       && coord.longitude > 170 && coord.longitude < 180 && coord.longitude > 0)
    {
        twoLines = YES;
        coords2 = malloc(sizeof(CLLocationCoordinate2D) * (numsegs - i));
        numsegs2 = numsegs - i;
        for(int j=0; j<numsegs2; j++)
        {
            coords2[j] = coords[i + j];
        }
        break;
    }
    prevCoord = coord;
}

//remove any previously added overlays
[mapView removeOverlays:mapView.overlays];

if(twoLines)
{
    MKPolyline *polyline = [MKPolyline polylineWithCoordinates:coords count:numsegs - numsegs2];
    free(coords);
    [mapView addOverlay:polyline];

    MKPolyline *polyline2 = [MKPolyline polylineWithCoordinates:coords2 count:numsegs2];
    free(coords2);
    [mapView addOverlay:polyline2];
}
else
{
    MKPolyline *polyline = [MKPolyline polylineWithCoordinates:coords count:numsegs];
    free(coords);
    [mapView addOverlay:polyline];
}

}

您现在已经创建了叠加层,现在您只需要在mapView:viewForOverlay中提供MKOverlayView.

- (MKOverlayView*)mapView:(MKMapView *)mapView viewForOverlay:(id<MKOverlay>)overlay
{
    MKPolyline *polyline = (MKPolyline*)overlay;
    MKPolylineView *view = [[[MKPolylineView alloc] initWithPolyline:polyline] autorelease];
    //choose your line params here
    view.lineWidth = 2;
    view.fillColor = [UIColor blueColor];
    return view;
}

希望这可以帮助.

截图http://s1-03.twitpicproxy.com/photos/large/489178500.png