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!
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);
}
}
}