Question

How can i calculate a MKPolygon from an CLLocationCoordinate2D (center point) and a CLLocationDistance (radius – green line)?

I want to show an Rect over an map with an given radius (the blue line)

Thanks

Answer 1

I adapted the answer from @Cyril Godefroy and added the conversion from How to make the union between two MKCoordinateRegion

- (MKMapRect) mapRectForCoordinateRegion:(MKCoordinateRegion)coordinateRegion {
    CLLocationCoordinate2D topLeftCoordinate = CLLocationCoordinate2DMake(coordinateRegion.center.latitude + (coordinateRegion.span.latitudeDelta / 2.0), coordinateRegion.center.longitude - (coordinateRegion.span.longitudeDelta / 2.0));

    MKMapPoint topLeftMapPoint = MKMapPointForCoordinate(topLeftCoordinate);

    CLLocationCoordinate2D bottomRightCoordinate = CLLocationCoordinate2DMake(coordinateRegion.center.latitude - (coordinateRegion.span.latitudeDelta / 2.0), coordinateRegion.center.longitude + (coordinateRegion.span.longitudeDelta / 2.0));

    MKMapPoint bottomRightMapPoint = MKMapPointForCoordinate(bottomRightCoordinate);

    MKMapRect mapRect = MKMapRectMake(topLeftMapPoint.x, topLeftMapPoint.y, fabs(bottomRightMapPoint.x - topLeftMapPoint.x), fabs(bottomRightMapPoint.y - topLeftMapPoint.y));

    return mapRect;
}

- (void) addSquareToMap:(CLLocation*)center withRadius:(float)radius{
    MKCoordinateRegion region = MKCoordinateRegionMakeWithDistance(center, radius*2, radius*2);
    MKMapRect rect = [self mapRectForCoordinateRegion:region];

    MKMapPoint leftBottom = MKMapPointMake(MKMapRectGetMinX(rect), MKMapRectGetMinY(rect));
    MKMapPoint leftTop = MKMapPointMake(MKMapRectGetMinX(rect), MKMapRectGetMaxY(rect));
    MKMapPoint rightTop = MKMapPointMake(MKMapRectGetMaxX(rect), MKMapRectGetMaxY(rect));
    MKMapPoint rightBottom = MKMapPointMake(MKMapRectGetMaxX(rect), MKMapRectGetMinY(rect));

    MKMapPoint rect[4] = {leftBottom, leftTop, rightTop, rightBottom};

    MKPolygon *polygon = [MKPolygon polygonWithPoints:rect count:4];
    poly.title = @"Square";

    // Add it to the map
    [map addOverlay:poly];
}

- (MKOverlayView *)mapView:(MKMapView *)mapView viewForOverlay:(id <MKOverlay>)overlay{
    if ([overlay isKindOfClass:[MKPolygon class]]){
        MKPolygonView*    aView = [[[MKPolygonView alloc] initWithPolygon:(MKPolygon*)overlay] autorelease];

        aView.fillColor = [[UIColor redColor] colorWithAlphaComponent:0.15];
        aView.strokeColor = [[UIColor redColor] colorWithAlphaComponent:0.7];
        aView.lineWidth = 3;

        return aView;
    }

return nil;
}