Dotted line on map view

Question

I can create a line between two points fairly easy with the below code (part of it anyways) How could I make the line dotted instead of solid? Also would it be possible to change the opacity the longer the line is?

- (MKOverlayRenderer *)mapView:(MKMapView *)mapView rendererForOverlay:(id < MKOverlay >)overlay
{
    MKPolylineRenderer *renderer =[[MKPolylineRenderer alloc] initWithPolyline:overlay];
    renderer.strokeColor = [UIColor orangeColor];
    renderer.lineWidth = 3.0;

    return renderer;
}