Eliminate Pin Overlap in the MKMapView

I am working with MKMapView Based application. I need a clarification whether it is possible to eliminate the pin OverLap in the MKMapView? Because at some places th开发者_运维问答ere are large number of pins displaying. It is difficult to me to identify the pins.

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If you have an Apple Developer Account, I would strongly recommend getting the Session 111 video from the 2011 WWDC Conference Sessions, entitled "Visualizing Information Geographically with MapKit". One of the segments specifically covers how to cluster content from large data sets to allow you to group or ungroup pins based on density at various zoom levels.

Their example is elegantly simple, but at the heart of the problem you want to replace a group of overlapping pins with a single pin and as you zoom in the single pin will split back into the individual pins.

How and when you decide to group things can be varied considerably. Apple's solution simply subdivides the map into a grid and any box that has more than 1 pin results in a group. You could also take an algorithmic approach such as using a kMeansCluster algorithm which is incredibly simple and you could feed all of your annotations through the algorithm and get an array of groups out the other side logically organized.

From there it's a matter of keeping track of all the individual pins and how they are grouped as you zoom in and out. You will only display a single annotation for each group or any individual pins that are left over. It's also possible to animate the transitions as the map zooms in and out so you can visually reinforce what is happening.

My own technique is too closely related to Apple's approach for me to post here so I'm hoping you can access the above video which covers almost all of these points.

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For this you have to implement clustering concept to your map.By using Apple demo code it's easy to implement clustering concept in our code. Reference link

Simply we can use following code for the Clustering

Steps to implement clustering

Step1 : The important thing is for clustering we use two mapviews(allAnnotationsMapView, ), One is for reference(allAnnotationsMapView).

@property (nonatomic, strong) MKMapView *allAnnotationsMapView;
@property (nonatomic, strong) IBOutlet MKMapView *mapView;

In viewDidLoad

    _allAnnotationsMapView = [[MKMapView alloc] initWithFrame:CGRectZero];

Step2 : Add all annotations to the _allAnnotationsMapView, In below _photos are the annotations array.

        [_allAnnotationsMapView addAnnotations:_photos];
        [self updateVisibleAnnotations];

Step3 : Add below methods for clustering, in this PhotoAnnotation is the custom annotation. MapViewDelegate methods

 - (void)mapView:(MKMapView *)aMapView regionDidChangeAnimated:(BOOL)animated {

    [self updateVisibleAnnotations];
}

- (void)mapView:(MKMapView *)aMapView didAddAnnotationViews:(NSArray *)views {

    for (MKAnnotationView *annotationView in views) {
        if (![annotationView.annotation isKindOfClass:[PhotoAnnotation class]]) {
            continue;
        }

        PhotoAnnotation *annotation = (PhotoAnnotation *)annotationView.annotation;

        if (annotation.clusterAnnotation != nil) {
            // animate the annotation from it's old container's coordinate, to its actual coordinate
            CLLocationCoordinate2D actualCoordinate = annotation.coordinate;
            CLLocationCoordinate2D containerCoordinate = annotation.clusterAnnotation.coordinate;

            // since it's displayed on the map, it is no longer contained by another annotation,
            // (We couldn't reset this in -updateVisibleAnnotations because we needed the reference to it here
            // to get the containerCoordinate)
            annotation.clusterAnnotation = nil;

            annotation.coordinate = containerCoordinate;

            [UIView animateWithDuration:0.3 animations:^{
                annotation.coordinate = actualCoordinate;
            }];
        }
    }
}

clustering Handling methods

    - (id<MKAnnotation>)annotationInGrid:(MKMapRect)gridMapRect usingAnnotations:(NSSet *)annotations {

    // first, see if one of the annotations we were already showing is in this mapRect
    NSSet *visibleAnnotationsInBucket = [self.mapView annotationsInMapRect:gridMapRect];
    NSSet *annotationsForGridSet = [annotations objectsPassingTest:^BOOL(id obj, BOOL *stop) {
        BOOL returnValue = ([visibleAnnotationsInBucket containsObject:obj]);
        if (returnValue)
        {
            *stop = YES;
        }
        return returnValue;
    }];

    if (annotationsForGridSet.count != 0) { 
        return [annotationsForGridSet anyObject];
    }

    // otherwise, sort the annotations based on their distance from the center of the grid square,
    // then choose the one closest to the center to show
    MKMapPoint centerMapPoint = MKMapPointMake(MKMapRectGetMidX(gridMapRect), MKMapRectGetMidY(gridMapRect));
    NSArray *sortedAnnotations = [[annotations allObjects] sortedArrayUsingComparator:^(id obj1, id obj2) {
        MKMapPoint mapPoint1 = MKMapPointForCoordinate(((id<MKAnnotation>)obj1).coordinate);
        MKMapPoint mapPoint2 = MKMapPointForCoordinate(((id<MKAnnotation>)obj2).coordinate);

        CLLocationDistance distance1 = MKMetersBetweenMapPoints(mapPoint1, centerMapPoint);
        CLLocationDistance distance2 = MKMetersBetweenMapPoints(mapPoint2, centerMapPoint);

        if (distance1 < distance2) {
            return NSOrderedAscending;
        } else if (distance1 > distance2) {
            return NSOrderedDescending;
        }

        return NSOrderedSame;
    }];

    PhotoAnnotation *photoAnn = sortedAnnotations[0];
    NSLog(@"lat long %f %f", photoAnn.coordinate.latitude, photoAnn.coordinate.longitude);

    return sortedAnnotations[0];
}

- (void)updateVisibleAnnotations {

    // This value to controls the number of off screen annotations are displayed.
    // A bigger number means more annotations, less chance of seeing annotation views pop in but decreased performance.
    // A smaller number means fewer annotations, more chance of seeing annotation views pop in but better performance.
    static float marginFactor = 2.0;

    // Adjust this roughly based on the dimensions of your annotations views.
    // Bigger numbers more aggressively coalesce annotations (fewer annotations displayed but better performance).
    // Numbers too small result in overlapping annotations views and too many annotations on screen.
    static float bucketSize = 60.0;

    // find all the annotations in the visible area + a wide margin to avoid popping annotation views in and out while panning the map.
    MKMapRect visibleMapRect = [self.mapView visibleMapRect];
    MKMapRect adjustedVisibleMapRect = MKMapRectInset(visibleMapRect, -marginFactor * visibleMapRect.size.width, -marginFactor * visibleMapRect.size.height);

    // determine how wide each bucket will be, as a MKMapRect square
    CLLocationCoordinate2D leftCoordinate = [self.mapView convertPoint:CGPointZero toCoordinateFromView:self.view];
    CLLocationCoordinate2D rightCoordinate = [self.mapView convertPoint:CGPointMake(bucketSize, 0) toCoordinateFromView:self.view];
    double gridSize = MKMapPointForCoordinate(rightCoordinate).x - MKMapPointForCoordinate(leftCoordinate).x;
    MKMapRect gridMapRect = MKMapRectMake(0, 0, gridSize, gridSize);

    // condense annotations, with a padding of two squares, around the visibleMapRect
    double startX = floor(MKMapRectGetMinX(adjustedVisibleMapRect) / gridSize) * gridSize;
    double startY = floor(MKMapRectGetMinY(adjustedVisibleMapRect) / gridSize) * gridSize;
    double endX = floor(MKMapRectGetMaxX(adjustedVisibleMapRect) / gridSize) * gridSize;
    double endY = floor(MKMapRectGetMaxY(adjustedVisibleMapRect) / gridSize) * gridSize;

    // for each square in our grid, pick one annotation to show
    gridMapRect.origin.y = startY;
    while (MKMapRectGetMinY(gridMapRect) <= endY) {
        gridMapRect.origin.x = startX;

        while (MKMapRectGetMinX(gridMapRect) <= endX) {
            NSSet *allAnnotationsInBucket = [self.allAnnotationsMapView annotationsInMapRect:gridMapRect];
            NSSet *visibleAnnotationsInBucket = [self.mapView annotationsInMapRect:gridMapRect];

            // we only care about PhotoAnnotations
            NSMutableSet *filteredAnnotationsInBucket = [[allAnnotationsInBucket objectsPassingTest:^BOOL(id obj, BOOL *stop) {
                return ([obj isKindOfClass:[PhotoAnnotation class]]);
            }] mutableCopy];

            if (filteredAnnotationsInBucket.count > 0) {
                PhotoAnnotation *annotationForGrid = (PhotoAnnotation *)[self annotationInGrid:gridMapRect usingAnnotations:filteredAnnotationsInBucket];

                [filteredAnnotationsInBucket removeObject:annotationForGrid];

                // give the annotationForGrid a reference to all the annotations it will represent
                annotationForGrid.containedAnnotations = [filteredAnnotationsInBucket allObjects];

                [self.mapView addAnnotation:annotationForGrid];

                for (PhotoAnnotation *annotation in filteredAnnotationsInBucket) {
                    // give all the other annotations a reference to the one which is representing them
                    annotation.clusterAnnotation = annotationForGrid;
                    annotation.containedAnnotations = nil;

                    // remove annotations which we've decided to cluster
                    if ([visibleAnnotationsInBucket containsObject:annotation]) {
                        CLLocationCoordinate2D actualCoordinate = annotation.coordinate;
                        [UIView animateWithDuration:0.3 animations:^{
                            annotation.coordinate = annotation.clusterAnnotation.coordinate;
                        } completion:^(BOOL finished) {
                            annotation.coordinate = actualCoordinate;
                            [self.mapView removeAnnotation:annotation];
                        }];
                    }
                }
            }

            gridMapRect.origin.x += gridSize;
        }

        gridMapRect.origin.y += gridSize;
    }
}

By following above steps we can achieve clustering on mapview, it is not necessary to use any third party code or framework. Please check the Apple sample code here. Please let me know if you have any doubts on this.

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It's quite easy to implement your own annotation clustering framework. Here's an example of a basic one that you can refer here.

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If your pins are overlapping then it must be that your zoom level is high for that place. You can think of removing some annotations in that zoom level until you dont have annotation overlaps and while zooming in you can add the annotations so that there are enough space between the annotations.