Raycasting algorithm with GPS coordinates

Question

I\'m making a small application with Google maps that determines if an entered address is part of a predefined service region.

The user enters an address, and a PHP

Answer 1

Well.... your second if() does not compensate for the fact that any of the subtractions may result in a negative number; it would only work if the coordinates are strictly ordered.

Update: On http://rosettacode.org/wiki/Ray-casting_algorithmn there's a whole bunch of algorithms in various languages that describe the process in detail (unfortunately, there is no version for PHP). What seems to be missing from your solution is picking a point that's guaranteed to be outside of the polygon; since you're dealing with longitude/lattitude that should be easy. Second, make sure your polygon is closed (i.e. go from the last point back to the first, if Google Maps doesn't already do so)