Check if CLLocation is in Shape?

Question

Im looking for a way to detect if the user is in The Netherlands or in Belgium. I don't want to call an API or use the users telephone services, so everything needs to be done locally and should be something easy and quick, small check. I have the users location each second and want to check each minute.

Goal: The user is travelling with our app and I want to show a different view when he/she arrived Belgium/Netherlands.

I've found two shape files from http://www.diva-gis.org/datadown with Netherlands and Belgium. These files are quite small and now Im looking for a way to create this method:

- (BOOL)isUserInNetherlands:(CLLocation)location;

which should check the location is it is in the content of the shapefile.

The shapefile for the Netherlands looks something like this:

I can convert the shapefile to a sqlLite database but not idea what to do next.

Any idea's?

Answer 1

One way to do this is:

1) convert the shapefile to geoJson

2) load the geoJson file data in your code.

3) create polygons from these gps points (note: CountryDetectorController is my controller class)

+ (MKPolygon *)overlaysFromPolygons:(NSArray *)polygons title:(NSString *)title;
{
    NSMutableArray *interiorPolygons = [NSMutableArray arrayWithCapacity:[polygons count] - 1];
    for (int i = 1; i < [polygons count]; i++) {
        [interiorPolygons addObject:[CountryDetectorController polygonFromPoints:polygons[i] interiorPolygons:nil]];
    }

    MKPolygon *overlayPolygon = [CountryDetectorController polygonFromPoints:polygons[0] interiorPolygons:interiorPolygons];
    overlayPolygon.title = title;


    return overlayPolygon;
}

+ (MKPolygon *)polygonFromPoints:(NSArray *)points interiorPolygons:(NSArray *)polygons;
{
    NSInteger numberOfCoordinates = [points count];
    CLLocationCoordinate2D *polygonPoints = malloc(numberOfCoordinates * sizeof(CLLocationCoordinate2D));

    NSInteger index = 0;
    for (NSArray *pointArray in points) {
        polygonPoints[index] = CLLocationCoordinate2DMake([pointArray[1] floatValue], [pointArray[0] floatValue]);
        index++;
    }

    MKPolygon *polygon;

    if (polygons) {
        polygon = [MKPolygon polygonWithCoordinates:polygonPoints count:numberOfCoordinates interiorPolygons:polygons];
    } else {
        polygon = [MKPolygon polygonWithCoordinates:polygonPoints count:numberOfCoordinates];
    }
    free(polygonPoints);

    return polygon;
}

4) create a CGPath from the polygon

+ (CGPathRef)pathForPolygon:(MKPolygon*)aPolygon;
{
    CGMutablePathRef mpr = CGPathCreateMutable();

    MKMapPoint *polygonPoints = aPolygon.points;
    size_t nCount = aPolygon.pointCount;

    for (int p = 0; p < nCount; p++)
    {
        MKMapPoint mp = polygonPoints[p];

        if (p == 0)
            CGPathMoveToPoint(mpr, NULL, mp.x, mp.y);
        else
            CGPathAddLineToPoint(mpr, NULL, mp.x, mp.y);
    }

    return mpr; //Keep in memory;
}

5) check if coordinate is in CGPath (pathsBelgium is an array with NSValue of CGPaths)

- (void)checkCoordinate:(CLLocationCoordinate2D)coordinate;
{
    MKMapPoint mapPoint = MKMapPointForCoordinate(coordinate);
    CGPoint mapPointAsCGP = CGPointMake(mapPoint.x, mapPoint.y);

    BOOL userIsInBelgium = FALSE;
    for(NSValue *valuePathBE in pathsBelgium)
    {
        CGPathRef pathBe;
        [valuePathBE getValue:&pathBe];

        BOOL pointInBelgium = CGPathContainsPoint(pathBe, NULL, mapPointAsCGP, FALSE);
        if(pointInBelgium)
        {
            userIsInBelgium = TRUE;
            break;
        }
    }

    NSLog(@"User is in Belgium: %i", userIsInBelgium);
}