How to detect taps on MKPolylines/Overlays like Maps.app?

Question

When displaying directions on the built-in Maps.app on the iPhone you can \"select\" one of the usually 3 route alternatives that are displayed by tapping on it. I wan\'t to

Answer 1

The solution proposed below by Jensemann is working great. See below code adapted for Swift 2, tested successfully on IOS 8 and 9 (XCode 7.1).

func didTapMap(gestureRecognizer: UIGestureRecognizer) {
    tapPoint = gestureRecognizer.locationInView(mapView)
    NSLog("tapPoint = %f,%f",tapPoint.x, tapPoint.y)
    //convert screen CGPoint tapPoint to CLLocationCoordinate2D...
    let tapCoordinate = mapView.convertPoint(tapPoint, toCoordinateFromView: mapView)
    let tapMapPoint = MKMapPointForCoordinate(tapCoordinate)
    print("tap coordinates = \(tapCoordinate)")
    print("tap map point = \(tapMapPoint)")

    // Now we test to see if one of the overlay MKPolyline paths were tapped
    var nearestDistance = Double(MAXFLOAT)
    let minDistance = 2000      // in meters, adjust as needed
    var nearestPoly = MKPolyline()
    // arrayPolyline below is an array of MKPolyline overlaid on the mapView
    for poly in arrayPolyline {                
        // ... get the distance ...
        let distance = distanceOfPoint(tapMapPoint, poly: poly)
        print("distance = \(distance)")
        // ... and find the nearest one
        if (distance < nearestDistance) {
            nearestDistance = distance
            nearestPoly = poly
        }
    }
    if (nearestDistance <= minDistance) {
        NSLog("Touched poly: %@\n    distance: %f", nearestPoly, nearestDistance);
    }
}


func distanceOfPoint(pt: MKMapPoint, poly: MKPolyline) -> Double {
    var distance: Double = Double(MAXFLOAT)
    var linePoints: [MKMapPoint] = []
    var polyPoints = UnsafeMutablePointer.alloc(poly.pointCount)
    for point in UnsafeBufferPointer(start: poly.points(), count: poly.pointCount) {
        linePoints.append(point)
        print("point: \(point.x),\(point.y)")
    }
    for n in 0...linePoints.count - 2 {
        let ptA = linePoints[n]
        let ptB = linePoints[n+1]
        let xDelta = ptB.x - ptA.x
        let yDelta = ptB.y - ptA.y
        if (xDelta == 0.0 && yDelta == 0.0) {
            // Points must not be equal
            continue
        }
        let u: Double = ((pt.x - ptA.x) * xDelta + (pt.y - ptA.y) * yDelta) / (xDelta * xDelta + yDelta * yDelta)
        var ptClosest = MKMapPoint()
        if (u < 0.0) {
            ptClosest = ptA
        } else if (u > 1.0) {
            ptClosest = ptB
        } else {
            ptClosest = MKMapPointMake(ptA.x + u * xDelta, ptA.y + u * yDelta);
        }
        distance = min(distance, MKMetersBetweenMapPoints(ptClosest, pt))
    }
    return distance
}