Check if CLLocation is in Shape? - ios

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);
}

Answer 2

A simpler method would be to get the user's location and then do a reverse geocode. Then you can extract the country from Apple's API instead of doing all the work yourself.
More here: https://developer.apple.com/library/ios/documentation/UserExperience/Conceptual/LocationAwarenessPG/UsingGeocoders/UsingGeocoders.html