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 replicate this functionality and check if a tap lies within a given MKPolyline.

Currently I detect taps on the MapView like this:

// Add Gesture Recognizer to MapView to detect taps
UITapGestureRecognizer *tap = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(handleMapTap:)];

// we require all gesture recognizer except other single-tap gesture recognizers to fail
for (UIGestureRecognizer *gesture in self.gestureRecognizers) {
    if ([gesture isKindOfClass:[UITapGestureRecognizer class]]) {
        UITapGestureRecognizer *systemTap = (UITapGestureRecognizer *)gesture;

        if (systemTap.numberOfTapsRequired > 1) {
            [tap requireGestureRecognizerToFail:systemTap];
        }
    } else {
        [tap requireGestureRecognizerToFail:gesture];
    }
}

[self addGestureRecognizer:tap];

I handle the taps as follows:

- (void)handleMapTap:(UITapGestureRecognizer *)tap {
    if ((tap.state & UIGestureRecognizerStateRecognized) == UIGestureRecognizerStateRecognized) {
        // Check if the overlay got tapped
        if (overlayView != nil) {
            // Get view frame rect in the mapView's coordinate system
            CGRect viewFrameInMapView = [overlayView.superview convertRect:overlayView.frame toView:self];
            // Get touch point in the mapView's coordinate system
            CGPoint point = [tap locationInView:self];

            // Check if the touch is within the view bounds
            if (CGRectContainsPoint(viewFrameInMapView, point)) {
                [overlayView handleTapAtPoint:[tap locationInView:self.directionsOverlayView]];
            }
        }
    }
}

This works as expected, now I need to check if the tap lies within the given MKPolyline overlayView (not strict, I the user taps somewhere near the polyline this should be handled as a hit).

What's a good way to do this?

- (void)handleTapAtPoint:(CGPoint)point {
    MKPolyline *polyline = self.polyline;

    // TODO: detect if point lies withing polyline with some margin
}

Thanks!

Midship

Answer 1

The question is rather old, but my answer may be useful to other people looking for a solution for this problem.

This code detects touches on poly lines with a maximum distance of 22 pixels in every zoom level. Just point your UITapGestureRecognizer to handleTap:

/** Returns the distance of |pt| to |poly| in meters
 *
 * from http://paulbourke.net/geometry/pointlineplane/DistancePoint.java
 *
 */
- (double)distanceOfPoint:(MKMapPoint)pt toPoly:(MKPolyline *)poly
{
    double distance = MAXFLOAT;
    for (int n = 0; n < poly.pointCount - 1; n++) {

        MKMapPoint ptA = poly.points[n];
        MKMapPoint ptB = poly.points[n + 1];

        double xDelta = ptB.x - ptA.x;
        double yDelta = ptB.y - ptA.y;

        if (xDelta == 0.0 && yDelta == 0.0) {

            // Points must not be equal
            continue;
        }

        double u = ((pt.x - ptA.x) * xDelta + (pt.y - ptA.y) * yDelta) / (xDelta * xDelta + yDelta * yDelta);
        MKMapPoint ptClosest;
        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;
}


/** Converts |px| to meters at location |pt| */
- (double)metersFromPixel:(NSUInteger)px atPoint:(CGPoint)pt
{
    CGPoint ptB = CGPointMake(pt.x + px, pt.y);

    CLLocationCoordinate2D coordA = [mapView convertPoint:pt toCoordinateFromView:mapView];
    CLLocationCoordinate2D coordB = [mapView convertPoint:ptB toCoordinateFromView:mapView];

    return MKMetersBetweenMapPoints(MKMapPointForCoordinate(coordA), MKMapPointForCoordinate(coordB));
}


#define MAX_DISTANCE_PX 22.0f
- (void)handleTap:(UITapGestureRecognizer *)tap
{
    if ((tap.state & UIGestureRecognizerStateRecognized) == UIGestureRecognizerStateRecognized) {

        // Get map coordinate from touch point
        CGPoint touchPt = [tap locationInView:mapView];
        CLLocationCoordinate2D coord = [mapView convertPoint:touchPt toCoordinateFromView:mapView];

        double maxMeters = [self metersFromPixel:MAX_DISTANCE_PX atPoint:touchPt];

        float nearestDistance = MAXFLOAT;
        MKPolyline *nearestPoly = nil;

        // for every overlay ...
        for (id <MKOverlay> overlay in mapView.overlays) {

            // .. if MKPolyline ...
            if ([overlay isKindOfClass:[MKPolyline class]]) {

                // ... get the distance ...
                float distance = [self distanceOfPoint:MKMapPointForCoordinate(coord)
                                                toPoly:overlay];

                // ... and find the nearest one
                if (distance < nearestDistance) {

                    nearestDistance = distance;
                    nearestPoly = overlay;
                }
            }
        }

        if (nearestDistance <= maxMeters) {

            NSLog(@"Touched poly: %@\n"
                   "    distance: %f", nearestPoly, nearestDistance);
        }
    }
}

Clown

This is a good solution. One question, what exactly is being calculated here? double u = ((pt.x - ptA.x) * xDelta + (pt.y - ptA.y) * yDelta) / (xDelta * xDelta + yDelta * yDelta); ... I kind of get lost from there, could you add some comments to explain what's being calculated from there and below? – Hamsun

@Hamsun that part is not my code. Please refer to paulbourke.net/geometry/pointlineplane – Clown

This works great, but once you get into the half million range for number of points it's a bit inefficient. Still, flawless detection +1. – Millstone

You generally don't need a half a million points to draw a good looking polyline. Look in to the Peucker algorithm to reduce the number of points for performance. – Heterotopia

Answer 2

@Jensemanns answer in Swift 4, which by the way was the only solution that I found that worked for me to detect clicks on a MKPolyline:

let map = MKMapView()
let mapTap = UITapGestureRecognizer(target: self, action: #selector(mapTapped(_:)))
map.addGestureRecognizer(mapTap)

func mapTapped(_ tap: UITapGestureRecognizer) {
    if tap.state == .recognized {
        // Get map coordinate from touch point
        let touchPt: CGPoint = tap.location(in: map)
        let coord: CLLocationCoordinate2D = map.convert(touchPt, toCoordinateFrom: map)
        let maxMeters: Double = meters(fromPixel: 22, at: touchPt)
        var nearestDistance: Float = MAXFLOAT
        var nearestPoly: MKPolyline? = nil
        // for every overlay ...
        for overlay: MKOverlay in map.overlays {
            // .. if MKPolyline ...
            if (overlay is MKPolyline) {
                // ... get the distance ...
                let distance: Float = Float(distanceOf(pt: MKMapPointForCoordinate(coord), toPoly: overlay as! MKPolyline))
                // ... and find the nearest one
                if distance < nearestDistance {
                    nearestDistance = distance
                    nearestPoly = overlay as! MKPolyline
                }

            }
        }

        if Double(nearestDistance) <= maxMeters {
            print("Touched poly: \(nearestPoly) distance: \(nearestDistance)")

        }
    }
}

func distanceOf(pt: MKMapPoint, toPoly poly: MKPolyline) -> Double {
    var distance: Double = Double(MAXFLOAT)
    for n in 0..<poly.pointCount - 1 {
        let ptA = poly.points()[n]
        let ptB = poly.points()[n + 1]
        let xDelta: Double = ptB.x - ptA.x
        let yDelta: Double = 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
}

func meters(fromPixel px: Int, at pt: CGPoint) -> Double {
    let ptB = CGPoint(x: pt.x + CGFloat(px), y: pt.y)
    let coordA: CLLocationCoordinate2D = map.convert(pt, toCoordinateFrom: map)
    let coordB: CLLocationCoordinate2D = map.convert(ptB, toCoordinateFrom: map)
    return MKMetersBetweenMapPoints(MKMapPointForCoordinate(coordA), MKMapPointForCoordinate(coordB))
}

Swift 5.x version

let map = MKMapView()
let mapTap = UITapGestureRecognizer(target: self, action: #selector(mapTapped))
map.addGestureRecognizer(mapTap)

@objc func mapTapped(_ tap: UITapGestureRecognizer) {
    if tap.state == .recognized {
        // Get map coordinate from touch point
        let touchPt: CGPoint = tap.location(in: map)
        let coord: CLLocationCoordinate2D = map.convert(touchPt, toCoordinateFrom: map)
        let maxMeters: Double = meters(fromPixel: 22, at: touchPt)
        var nearestDistance: Float = MAXFLOAT
        var nearestPoly: MKPolyline? = nil
        // for every overlay ...
        for overlay: MKOverlay in map.overlays {
            // .. if MKPolyline ...
            if (overlay is MKPolyline) {
                // ... get the distance ...
                let distance: Float = Float(distanceOf(pt: MKMapPoint(coord), toPoly: overlay as! MKPolyline))
                // ... and find the nearest one
                if distance < nearestDistance {
                    nearestDistance = distance
                    nearestPoly = overlay as? MKPolyline
                }

            }
        }

        if Double(nearestDistance) <= maxMeters {
            print("Touched poly: \(String(describing: nearestPoly)) distance: \(nearestDistance)")

        }
    }
}

private func distanceOf(pt: MKMapPoint, toPoly poly: MKPolyline) -> Double {
    var distance: Double = Double(MAXFLOAT)
    for n in 0..<poly.pointCount - 1 {
        let ptA = poly.points()[n]
        let ptB = poly.points()[n + 1]
        let xDelta: Double = ptB.x - ptA.x
        let yDelta: Double = 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 = MKMapPoint(x: ptA.x + u * xDelta, y: ptA.y + u * yDelta)
        }

        distance = min(distance, ptClosest.distance(to: pt))
    }
    return distance
}

private func meters(fromPixel px: Int, at pt: CGPoint) -> Double {
    let ptB = CGPoint(x: pt.x + CGFloat(px), y: pt.y)
    let coordA: CLLocationCoordinate2D = map.convert(pt, toCoordinateFrom: map)
    let coordB: CLLocationCoordinate2D = map.convert(ptB, toCoordinateFrom: map)
    return MKMapPoint(coordA).distance(to: MKMapPoint(coordB))
}

Predicament

Why doesn't this works on MKPolyline crossing 360th meridian Source : CLLocationCoordinate2D(latitude: -33.8392932, longitude: 151.21519799999999) Destination: CLLocationCoordinate2D(latitude: 39.645516999999998, longitude: -104.598724) – Tillfourd

Why the double check? if tap.state == .recognized && tap.state == .recognized – Would

@JasonSilver, that was a typo. Thanks for pointing it out, I have updated the sample. – Predicament

Working for me! we can also use the touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) . – Ellingson

Daft question, I'm sure, but what would be a meaningful name for that u variable in the distanceOf functions? My linter is erroring, but I don't know what to rename it to as I don't know what it is. Thanks. – Hustle

It also works with SwiftUI and MapKit inside a UIViewRepresentable. Just put everything inside the UVR's coordinator class and call let mapTap = UITapGestureRecognizer(target: context.coordinator, action: #selector(context.coordinator.mapTapped)) mapView.addGestureRecognizer(mapTap) from inside the makeUIView function. Thanks for sharing!!! – Celluloid

Answer 3

You can refer my answer may it will help you to find desired solution.

I've added gesture on my MKMapView.

[mapV addGestureRecognizer:[[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(mapTapped:)]];

This is how i handled my gesture and find out whether the tap is on Overlay view or not.

   - (void)mapTapped:(UITapGestureRecognizer *)recognizer
    {

         MKMapView *mapView = (MKMapView *)recognizer.view;

         CGPoint tapPoint = [recognizer locationInView:mapView];
         NSLog(@"tapPoint = %f,%f",tapPoint.x, tapPoint.y);

         //convert screen CGPoint tapPoint to CLLocationCoordinate2D...
         CLLocationCoordinate2D tapCoordinate = [mapView convertPoint:tapPoint toCoordinateFromView:mapView];

         //convert CLLocationCoordinate2D tapCoordinate to MKMapPoint...
         MKMapPoint point = MKMapPointForCoordinate(tapCoordinate);

         if (mapView.overlays.count > 0 ) {
              for (id<MKOverlay> overlay in mapView.overlays)
              {

                   if ([overlay isKindOfClass:[MKCircle class]])
                   {
                        MKCircle *circle = overlay;
                        MKCircleRenderer *circleRenderer = (MKCircleRenderer *)[mapView rendererForOverlay:circle];

                        //convert MKMapPoint tapMapPoint to point in renderer's context...
                        CGPoint datpoint = [circleRenderer pointForMapPoint:point];
                        [circleRenderer invalidatePath];


                        if (CGPathContainsPoint(circleRenderer.path, nil, datpoint, false)){

                             NSLog(@"tapped on overlay");
                             break;
                   }

              }

         }

       }
    }

Thanks. This may help you hopefully.

Hyposensitize

Answer 4

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<MKMapPoint>.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
}

Thurible

Answer 5

Updated for Swift 3

func isTappedOnPolygon(with tapGesture:UITapGestureRecognizer, on mapView: MKMapView) -> Bool {
    let tappedMapView = tapGesture.view
    let tappedPoint = tapGesture.location(in: tappedMapView)
    let tappedCoordinates = mapView.convert(tappedPoint, toCoordinateFrom: tappedMapView)
    let point:MKMapPoint = MKMapPointForCoordinate(tappedCoordinates)

    let overlays = mapView.overlays.filter { o in
        o is MKPolygon
    }

    for overlay in overlays {
        let polygonRenderer = MKPolygonRenderer(overlay: overlay)
        let datPoint = polygonRenderer.point(for: point)
        polygonRenderer.invalidatePath()

        return polygonRenderer.path.contains(datPoint)
    }
    return false
}

Jefferyjeffie

How do you add the gesture recognizer to the mapview for this? – Goebbels

This code is getting always false even the point is existed in polyline. – Carolyncarolyne

@Anilkumar this answer is for a polygon. For a polyline, you need to give it width. polylineRenderer.path.copy(strokingWithWidth: 30 * UIScreen.main.scale . . . – Jilly

Answer 6

@Rashwan L : Updated his answer to Swift 4.2

let map = MKMapView()
let mapTap = UITapGestureRecognizer(target: self, action: #selector(mapTapped(_:)))
 map.addGestureRecognizer(mapTap)

 @objc private func mapTapped(_ tap: UITapGestureRecognizer) {
    if tap.state == .recognized && tap.state == .recognized {
        // Get map coordinate from touch point
        let touchPt: CGPoint = tap.location(in: skyMap)
        let coord: CLLocationCoordinate2D = skyMap.convert(touchPt, toCoordinateFrom: skyMap)
        let maxMeters: Double = meters(fromPixel: 22, at: touchPt)
        var nearestDistance: Float = MAXFLOAT
        var nearestPoly: MKPolyline? = nil
        // for every overlay ...
        for overlay: MKOverlay in skyMap.overlays {
            // .. if MKPolyline ...
            if (overlay is MKPolyline) {
                // ... get the distance ...
                let distance: Float = Float(distanceOf(pt: MKMapPoint(coord), toPoly: overlay as! MKPolyline))
                // ... and find the nearest one
                if distance < nearestDistance {
                    nearestDistance = distance
                    nearestPoly = overlay as? MKPolyline
                }

            }
        }

        if Double(nearestDistance) <= maxMeters {
            print("Touched poly: \(nearestPoly) distance: \(nearestDistance)")

        }
    }
}

private func distanceOf(pt: MKMapPoint, toPoly poly: MKPolyline) -> Double {
    var distance: Double = Double(MAXFLOAT)
    for n in 0..<poly.pointCount - 1 {
        let ptA = poly.points()[n]
        let ptB = poly.points()[n + 1]
        let xDelta: Double = ptB.x - ptA.x
        let yDelta: Double = 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 = MKMapPoint(x: ptA.x + u * xDelta, y: ptA.y + u * yDelta)
        }

        distance = min(distance, ptClosest.distance(to: pt))
    }
    return distance
}

private func meters(fromPixel px: Int, at pt: CGPoint) -> Double {
    let ptB = CGPoint(x: pt.x + CGFloat(px), y: pt.y)
    let coordA: CLLocationCoordinate2D = skyMap.convert(pt, toCoordinateFrom: skyMap)
    let coordB: CLLocationCoordinate2D = skyMap.convert(ptB, toCoordinateFrom: skyMap)
    return MKMapPoint(coordA).distance(to: MKMapPoint(coordB))
}

Iz

Does not work when MKPolyline crosses 180th meridian – Tillfourd

Sorry i don´t know :) Just try it. – Iz

Answer 7

The real "cookie" in this code is the point -> line distance function. I was so happy to find it and it worked great (swift 4, iOS 11). Thanks to everyone, especially @Jensemann. Here is my refactoring of it:

public extension MKPolyline {

    // Return the point on the polyline that is the closest to the given point
    // along with the distance between that closest point and the given point.
    //
    // Thanks to:
    // http://paulbourke.net/geometry/pointlineplane/
    // https://mcmap.net/q/479000/-how-to-detect-taps-on-mkpolylines-overlays-like-maps-app

    public func closestPoint(to: MKMapPoint) -> (point: MKMapPoint, distance: CLLocationDistance) {

        var closestPoint = MKMapPoint()
        var distanceTo = CLLocationDistance.infinity

        let points = self.points()
        for i in 0 ..< pointCount - 1 {
            let endPointA = points[i]
            let endPointB = points[i + 1]

            let deltaX: Double = endPointB.x - endPointA.x
            let deltaY: Double = endPointB.y - endPointA.y
            if deltaX == 0.0 && deltaY == 0.0 { continue } // Points must not be equal

            let u: Double = ((to.x - endPointA.x) * deltaX + (to.y - endPointA.y) * deltaY) / (deltaX * deltaX + deltaY * deltaY) // The magic sauce. See the Paul Bourke link above.

            let closest: MKMapPoint
            if u < 0.0 { closest = endPointA }
            else if u > 1.0 { closest = endPointB }
            else { closest = MKMapPointMake(endPointA.x + u * deltaX, endPointA.y + u * deltaY) }

            let distance = MKMetersBetweenMapPoints(closest, to)
            if distance < distanceTo {
                closestPoint = closest
                distanceTo = distance
            }
        }

        return (closestPoint, distanceTo)
    }
}

Sedgewake

Does not work when MKPolyline crosses 180th meridian – Tillfourd

Answer 8

It's an old thread however I found a different way which may help anyone. Tested on multiple routes overlay in Swift 4.2.

 @IBAction func didTapGesture(_ sender: UITapGestureRecognizer) {
        let touchPoint = sender.location(in: mapView)
        let touchCoordinate = mapView.convert(touchPoint, toCoordinateFrom: mapView)
        let mapPoint = MKMapPoint(touchCoordinate)

        for overlay in mapView.overlays {
            if overlay is MKPolyline {
                if let polylineRenderer = mapView.renderer(for: overlay) as? MKPolylineRenderer {
                    let polylinePoint = polylineRenderer.point(for: mapPoint)

                    if polylineRenderer.path.contains(polylinePoint) {
                        print("polyline was tapped")
                    }
                }
            }
        }
 }

Quenchless

This is not working as expected. The function prints "polyline was tapped" even when some parts outside the polyline is tapped. Checkout and play with repo github.com/abin0992/SupplyLineTouchBug I have explained where to tap to see this logic goes wrong. – Tillfourd