Drawing a route in MapKit in iOS

The following viewDidLoad will (1) set two locations, (2) remove all the previous annotations, and (3) call user defined helper functions (to get route points and draw the route).

-(void)viewDidLoad
{
    [super viewDidLoad];

    // Origin Location.
    CLLocationCoordinate2D loc1;
    loc1.latitude = 29.0167;
    loc1.longitude = 77.3833;
    Annotation *origin = [[Annotation alloc] initWithTitle:@"loc1" subTitle:@"Home1" andCoordinate:loc1];
    [objMapView addAnnotation:origin];

    // Destination Location.
    CLLocationCoordinate2D loc2;
    loc2.latitude = 19.076000;
    loc2.longitude = 72.877670;
    Annotation *destination = [[Annotation alloc] initWithTitle:@"loc2" subTitle:@"Home2" andCoordinate:loc2];
    [objMapView addAnnotation:destination];

    if(arrRoutePoints) // Remove all annotations
        [objMapView removeAnnotations:[objMapView annotations]];

    arrRoutePoints = [self getRoutePointFrom:origin to:destination];
    [self drawRoute];
    [self centerMap];
}

The following is the MKMapViewDelegate method, which draws overlay (iOS 4.0 and later).

/* MKMapViewDelegate Meth0d -- for viewForOverlay*/
- (MKOverlayView*)mapView:(MKMapView*)theMapView viewForOverlay:(id <MKOverlay>)overlay
{
    MKPolylineView *view = [[MKPolylineView alloc] initWithPolyline:objPolyline];
    view.fillColor = [UIColor blackColor];
    view.strokeColor = [UIColor blackColor];
    view.lineWidth = 4;
    return view;
}

The following function will get both the locations and prepare URL to get all the route points. And of course, will call stringWithURL.

/* This will get the route coordinates from the Google API. */
- (NSArray*)getRoutePointFrom:(Annotation *)origin to:(Annotation *)destination
{
    NSString* saddr = [NSString stringWithFormat:@"%f,%f", origin.coordinate.latitude, origin.coordinate.longitude];
    NSString* daddr = [NSString stringWithFormat:@"%f,%f", destination.coordinate.latitude, destination.coordinate.longitude];

    NSString* apiUrlStr = [NSString stringWithFormat:@"http://maps.google.com/maps?output=dragdir&saddr=%@&daddr=%@", saddr, daddr];
    NSURL* apiUrl = [NSURL URLWithString:apiUrlStr];

    NSError *error;
    NSString *apiResponse = [NSString stringWithContentsOfURL:apiUrl encoding:NSUTF8StringEncoding error:&error];
    NSString* encodedPoints = [apiResponse stringByMatching:@"points:\\\"([^\\\"]*)\\\"" capture:1L];

    return [self decodePolyLine:[encodedPoints mutableCopy]];
}

The following code is the real magic (decoder for the response we got from the API). I would not modify that code unless I know what I am doing 🙂

- (NSMutableArray *)decodePolyLine:(NSMutableString *)encodedString
{
    [encodedString replaceOccurrencesOfString:@"\\\\" withString:@"\\"
                                  options:NSLiteralSearch
                                    range:NSMakeRange(0, [encodedString length])];
    NSInteger len = [encodedString length];
    NSInteger index = 0;
    NSMutableArray *array = [[NSMutableArray alloc] init];
    NSInteger lat=0;
    NSInteger lng=0;
    while (index < len) {
        NSInteger b;
        NSInteger shift = 0;
        NSInteger result = 0;
        do {
            b = [encodedString characterAtIndex:index++] - 63;
            result |= (b & 0x1f) << shift;
            shift += 5;
        } while (b >= 0x20);
        NSInteger dlat = ((result & 1) ? ~(result >> 1) : (result >> 1));
        lat += dlat;
        shift = 0;
        result = 0;
        do {
            b = [encodedString characterAtIndex:index++] - 63;
            result |= (b & 0x1f) << shift;
            shift += 5;
       } while (b >= 0x20);
        NSInteger dlng = ((result & 1) ? ~(result >> 1) : (result >> 1));
        lng += dlng;
        NSNumber *latitude = [[NSNumber alloc] initWithFloat:lat * 1e-5];
        NSNumber *longitude = [[NSNumber alloc] initWithFloat:lng * 1e-5];
        printf("\n[%f,", [latitude doubleValue]);
        printf("%f]", [longitude doubleValue]);
        CLLocation *loc = [[CLLocation alloc] initWithLatitude:[latitude floatValue] longitude:[longitude floatValue]];
        [array addObject:loc];
    }
    return array;
}

This function will draw a route and will add an overlay.

- (void)drawRoute
{
    int numPoints = [arrRoutePoints count];
    if (numPoints > 1)
    {
        CLLocationCoordinate2D* coords = malloc(numPoints * sizeof(CLLocationCoordinate2D));
        for (int i = 0; i < numPoints; i++)
        {
            CLLocation* current = [arrRoutePoints objectAtIndex:i];
            coords[i] = current.coordinate;
        }

        self.objPolyline = [MKPolyline polylineWithCoordinates:coords count:numPoints];
        free(coords);

        [objMapView addOverlay:objPolyline];
        [objMapView setNeedsDisplay];
    }
}

The following code will center align the map.

- (void)centerMap
{
    MKCoordinateRegion region;

    CLLocationDegrees maxLat = -90;
    CLLocationDegrees maxLon = -180;
    CLLocationDegrees minLat = 90;
    CLLocationDegrees minLon = 180;

    for(int idx = 0; idx < arrRoutePoints.count; idx++)
    {
        CLLocation* currentLocation = [arrRoutePoints objectAtIndex:idx];

        if(currentLocation.coordinate.latitude > maxLat)
            maxLat = currentLocation.coordinate.latitude;
        if(currentLocation.coordinate.latitude < minLat)
            minLat = currentLocation.coordinate.latitude;
        if(currentLocation.coordinate.longitude > maxLon)
            maxLon = currentLocation.coordinate.longitude;
        if(currentLocation.coordinate.longitude < minLon)
            minLon = currentLocation.coordinate.longitude;
    }

    region.center.latitude     = (maxLat + minLat) / 2;
    region.center.longitude    = (maxLon + minLon) / 2;
    region.span.latitudeDelta  = maxLat - minLat;
    region.span.longitudeDelta = maxLon - minLon;

    [objMapView setRegion:region animated:YES];
}

I hope this would help someone.