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    <p>I've implemented this for drawing a great circle route for aircraft going between two airports using MKPolyline. </p> <pre><code>+ (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&lt;=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&lt;numsegs; i++) { CLLocationCoordinate2D coord = coords[i]; if(prevCoord.longitude &lt; -170 &amp;&amp; prevCoord.longitude &gt; -180 &amp;&amp; prevCoord.longitude &lt; 0 &amp;&amp; coord.longitude &gt; 170 &amp;&amp; coord.longitude &lt; 180 &amp;&amp; coord.longitude &gt; 0) { twoLines = YES; coords2 = malloc(sizeof(CLLocationCoordinate2D) * (numsegs - i)); numsegs2 = numsegs - i; for(int j=0; j&lt;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]; } } </code></pre> <p>You've now created the overlay(s), now you just need to provide an MKOverlayView in mapView:viewForOverlay.</p> <pre><code>- (MKOverlayView*)mapView:(MKMapView *)mapView viewForOverlay:(id&lt;MKOverlay&gt;)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; } </code></pre> <p>Hope this helps.</p> <p><a href="http://s1-03.twitpicproxy.com/photos/large/489178500.png">Screenshot http://s1-03.twitpicproxy.com/photos/large/489178500.png</a></p>
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