Function to spread MapView annotation such that none are overlapping

Question

It seems like many have touched on this issue of overlapping MKAnnotation Views, and gracefully spreading them out at the end of a zoom, and at viewdidload. So I think I am just going to bite the bullet and dev out a solution, but before I do I wanted to ask advice on the algo to implement. Previous posts about this topic that had no viable solution offered:

ios sdk MKMapView overlapping pins? Laying out overlapping rectangles

and many more...

So the function I am thinking of is this: (Note all the CGRects are the same size)

-(NSArray *)spreadOutTheseViews:(NSArray *)arrayofCGRects{



    ////////////////////////////////////
    //find out who overlaps with who..
    ////////////////////////////////////

    NSMutableArray *arrayOfArraysOfRects = [[NSMutableArray alloc] init];

    // 1. make an array to let you know which Rects have already been added to one of the sets
    int n = (int)[arrayofCGRects count];
    NSMutableArray *addedAlready = [[NSMutableArray alloc] init];
    for (id obj in arrayofCGRects ) {
        [addedAlready addObject:@0];
    }

    // 2. go through and add them if they overlap
    for (int i=0; i<[arrayofCGRects count]; i++) {
        if ([[addedAlready objectAtIndex:i] isEqualToValue:@(0)]) {

            CGRect rect1 = [[arrayOfArraysOfRects objectAtIndex:i] CGRectValue];
            [arrayOfArraysOfRects addObject:[[NSMutableArray alloc] initWithObjects:@(i), nil]];
            [addedAlready insertObject:@(1) atIndex:i];

            for (int j=0; j<[arrayofCGRects count]; j++){
                if (i!=j && [[addedAlready objectAtIndex:j] isEqualToValue:@(0)] ) {
                    CGRect rect2 = [[arrayOfArraysOfRects objectAtIndex:j] CGRectValue];
                    if (CGRectIntersectsRect(rect1,rect2)){
                        // check if they are overlapping, if so, add it to
                        [[arrayOfArraysOfRects lastObject] addObject:@(j)];
                        [addedAlready insertObject:@(1) atIndex:j];
                    }
                }
            }
        }
    }
    NSMutableArray *arrayofCGPoints = [[NSMutableArray alloc] init];
    //3. now that we have "clusters" of overlapping rects.. push them away from each other..
    for(NSArray *indexArray in arrayOfArraysOfRects){

        if ([indexArray count]==1){
            // just simply add the CGPoint
            CGRect rect =  [[arrayofCGRects objectAtIndex:(NSInteger)[indexArray firstObject]] CGRectValue];
            [arrayofCGPoints addObject:[NSValue valueWithCGPoint:rect.origin] ];

        }else{

            // heart of the algo..
            // Idea 1: get the average of the CGPoints to find the center of all of them, then find a ring with a specific radius that we can put them all on. Note this is a packing problem that I really dont have a better solution for..


        }



    }

    return arrayofCGPoints;

}

Any help here would be greatly appreciated..

score 0 · Answer 1 · answered Nov 10 '14 at 08:10

Well its not the prettiest of solutions.. but I got something working for now in case someone finds this useful.. Also please still post if you have a more elegant solution!

-(NSArray *)spreadOutTheseViews:(NSArray *)arrayofCGRects{

bool doAnyOverlapStill = true;
int counter=0;
NSMutableArray *newArrayOfCGRects = [[NSMutableArray alloc] initWithArray:arrayofCGRects];

while (doAnyOverlapStill) {
    NSLog([NSString stringWithFormat:@"number of iters %d",counter]);

    for (int i=0; i<[arrayofCGRects count]; i++) {
        CGRect rect1 = [[newArrayOfCGRects objectAtIndex:i] CGRectValue];
        for (int j=0; j<=i; j++){
            if (i!=j) {
                CGRect rect2 = [[newArrayOfCGRects objectAtIndex:j] CGRectValue];
                bool intersect = CGRectIntersectsRect(rect1,rect2);
                if (intersect){

                    if (counter%4==0) {
                        // LEFT
                        NSLog(@"LEFT");
                        // which ever one is on the left, move it further to the left
                        double neededDistanceAdjustment =  5+MAX(rect1.size.width,rect2.size.width) - fabsf(rect2.origin.x - rect1.origin.x);
                        if (rect1.origin.x < rect2.origin.x) {
                            // move rect 1 left (subtract)
                            rect1.origin.x -= neededDistanceAdjustment;
                            [newArrayOfCGRects removeObjectAtIndex:i];
                            [newArrayOfCGRects insertObject:[NSValue valueWithCGRect:rect1] atIndex:i];

                        }else{
                            // move rect 2 left (subtract)
                            rect2.origin.x -= neededDistanceAdjustment;
                            [newArrayOfCGRects removeObjectAtIndex:j];
                            [newArrayOfCGRects insertObject:[NSValue valueWithCGRect:rect2] atIndex:j];
                        }

                    }else if (counter%4==1) {
                        // UP
                        NSLog(@"UP");
                        double neededDistanceAdjustment =  5+MAX(rect1.size.height,rect2.size.height) - fabsf(rect2.origin.y - rect1.origin.y);
                        if (rect1.origin.y < rect2.origin.y) {
                            // move rect 1 up (subtract)
                            rect1.origin.y -= neededDistanceAdjustment;
                            [newArrayOfCGRects removeObjectAtIndex:i];
                            [newArrayOfCGRects insertObject:[NSValue valueWithCGRect:rect1] atIndex:i];

                        }else{
                            // move rect 2 up (subtract)
                            rect2.origin.y -= neededDistanceAdjustment;
                            [newArrayOfCGRects removeObjectAtIndex:j];
                            [newArrayOfCGRects insertObject:[NSValue valueWithCGRect:rect2] atIndex:j];
                        }

                    }else if (counter%4==2) {
                        //RIGHT

                        NSLog(@"RIGHT");
                        double neededDistanceAdjustment =  5+MAX(rect1.size.width,rect2.size.width) - fabsf(rect2.origin.x - rect1.origin.x);

                        if (rect1.origin.x > rect2.origin.x) {
                            // move rect 1 right (add)
                            rect1.origin.y += neededDistanceAdjustment;
                            [newArrayOfCGRects removeObjectAtIndex:i];
                            [newArrayOfCGRects insertObject:[NSValue valueWithCGRect:rect1] atIndex:i];

                        }else{
                            // move rect 2 right (add)
                            rect2.origin.y += neededDistanceAdjustment;
                            [newArrayOfCGRects removeObjectAtIndex:j];
                            [newArrayOfCGRects insertObject:[NSValue valueWithCGRect:rect2] atIndex:j];
                        }

                    }else if (counter%4==3) {
                        // DOWN

                        NSLog(@"DOWN");
                        double neededDistanceAdjustment =  5+MAX(rect1.size.height,rect2.size.height) - fabsf(rect2.origin.y - rect1.origin.y);
                        if (rect1.origin.y > rect2.origin.y) {
                            // move rect 1 down (add)
                            rect1.origin.y += neededDistanceAdjustment;
                            [newArrayOfCGRects removeObjectAtIndex:i];
                            [newArrayOfCGRects insertObject:[NSValue valueWithCGRect:rect1] atIndex:i];

                        }else{
                            // move rect 2 down (add)
                            rect2.origin.y += neededDistanceAdjustment;
                            [newArrayOfCGRects removeObjectAtIndex:j];
                            [newArrayOfCGRects insertObject:[NSValue valueWithCGRect:rect2] atIndex:j];
                        }
                    }
                    // update newArrayOfCGRects
                    counter++;

                }
            }
        }
    }
    if (counter>100) {
        NSLog(@"error!!");
        return arrayofCGRects;


    }

    doAnyOverlapStill = [self doRectsOverlap:newArrayOfCGRects];
    if (!doAnyOverlapStill) {
        return newArrayOfCGRects;
    }
}

return arrayofCGRects;

}

Clarification question: are you talking about point clustering, or about the annotations views not overlapping each other for aesthetic reasons? — incanus, Nov 10 '14 at 18:42
Yes, the latter, as better demonstrated here: http://stackoverflow.com/questions/17710770/ios-sdk-mkmapview-overlapping-pins — fchaubard, Nov 10 '14 at 23:58

Function to spread MapView annotation such that none are overlapping

1 Answers1