iPhone Map Kit cluster pinpoints

Question

Regarding iPhone Map Kit cluster pinpoints:

I have 1000\'s of marks that I want to show on the map but it\'s just too many to handle so I want to cluster them.

Answer 1

Inspired by WWDC 2011 video, this code works very well for me. Maybe not the fastest of all proposed here but it's for free and it's definitely the simplest.

It basically use 2 maps. One is hidden and hold every single annotation (allAnnotationMapView in my code). One is visible and show only the clusters or the annotations if single (mapView in my code).

- (void)didZoom:(UIGestureRecognizer*)gestureRecognizer {
    if (gestureRecognizer.state == UIGestureRecognizerStateEnded){
        [self updateVisibleAnnotations];
    }
}
- (void)updateVisibleAnnotations {
    static float marginFactor = 2.0f;
    static float bucketSize = 50.0f;
    MKMapRect visibleMapRect = [self.mapView visibleMapRect];
    MKMapRect adjustedVisibleMapRect = MKMapRectInset(visibleMapRect, -marginFactor * visibleMapRect.size.width, -marginFactor * visibleMapRect.size.height);

    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);

    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;

    gridMapRect.origin.y = startY;
    while(MKMapRectGetMinY(gridMapRect) <= endY) {
        gridMapRect.origin.x = startX;
        while (MKMapRectGetMinX(gridMapRect) <= endX) {
            NSSet *allAnnotationsInBucket = [self.allAnnotationMapView annotationsInMapRect:gridMapRect];
            NSSet *visibleAnnotationsInBucket = [self.mapView annotationsInMapRect:gridMapRect];

            NSMutableSet *filteredAnnotationsInBucket = [[allAnnotationsInBucket objectsPassingTest:^BOOL(id obj, BOOL *stop) {
                BOOL isPointMapItem = [obj isKindOfClass:[PointMapItem class]];
                BOOL shouldBeMerged = NO;
                if (isPointMapItem) {
                    PointMapItem *pointItem = (PointMapItem *)obj;
                    shouldBeMerged = pointItem.shouldBeMerged;
                }
                return shouldBeMerged;
            }] mutableCopy];
            NSSet *notMergedAnnotationsInBucket = [allAnnotationsInBucket objectsPassingTest:^BOOL(id obj, BOOL *stop) {
                BOOL isPointMapItem = [obj isKindOfClass:[PointMapItem class]];
                BOOL shouldBeMerged = NO;
                if (isPointMapItem) {
                    PointMapItem *pointItem = (PointMapItem *)obj;
                    shouldBeMerged = pointItem.shouldBeMerged;
                }
                return isPointMapItem && !shouldBeMerged;
            }];
            for (PointMapItem *item in notMergedAnnotationsInBucket) {
                [self.mapView addAnnotation:item];
            }

            if(filteredAnnotationsInBucket.count > 0) {
                PointMapItem *annotationForGrid = (PointMapItem *)[self annotationInGrid:gridMapRect usingAnnotations:filteredAnnotationsInBucket];
                [filteredAnnotationsInBucket removeObject:annotationForGrid];
                annotationForGrid.containedAnnotations = [filteredAnnotationsInBucket allObjects];
                [self.mapView addAnnotation:annotationForGrid];
                //force reload of the image because it's not done if annotationForGrid is already present in the bucket!!
                MKAnnotationView* annotationView = [self.mapView viewForAnnotation:annotationForGrid];
                NSString *imageName = [AnnotationsViewUtils imageNameForItem:annotationForGrid selected:NO];
                UILabel *countLabel = [[UILabel alloc] initWithFrame:CGRectMake(15, 2, 8, 8)];
                [countLabel setFont:[UIFont fontWithName:POINT_FONT_NAME size:10]];
                [countLabel setTextColor:[UIColor whiteColor]];
                [annotationView addSubview:countLabel];
                imageName = [AnnotationsViewUtils imageNameForItem:annotationForGrid selected:NO];
                annotationView.image = [UIImage imageNamed:imageName];

                if (filteredAnnotationsInBucket.count > 0){
                    [self.mapView deselectAnnotation:annotationForGrid animated:NO];
                }
                for (PointMapItem *annotation in filteredAnnotationsInBucket) {
                    [self.mapView deselectAnnotation:annotation animated:NO];
                    annotation.clusterAnnotation = annotationForGrid;
                    annotation.containedAnnotations = nil;
                    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;
    }
}

- (id)annotationInGrid:(MKMapRect)gridMapRect usingAnnotations:(NSSet *)annotations {
    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];
    }
    MKMapPoint centerMapPoint = MKMapPointMake(MKMapRectGetMinX(gridMapRect), MKMapRectGetMidY(gridMapRect));
    NSArray *sortedAnnotations = [[annotations allObjects] sortedArrayUsingComparator:^(id obj1, id obj2) {
        MKMapPoint mapPoint1 = MKMapPointForCoordinate(((id)obj1).coordinate);
        MKMapPoint mapPoint2 = MKMapPointForCoordinate(((id)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;
    }];
    return [sortedAnnotations objectAtIndex:0];
}