I realise that you can open the google maps app ready for directions by doing something like this:
NSString* urlString = @\"http://maps.google.com/maps?saddr
String url = "http://maps.google.com/maps?f=d&daddr="+latitude+","+longitude+"&dirflg=r";
Intent intent = new Intent(android.content.Intent.ACTION_VIEW, Uri.parse(url));
intent.setClassName("com.google.android.apps.maps", "com.google.android.maps.MapsActivity");
startActivity(intent);
dirflg=r is for public transport.