Geo Fencing - point inside/outside polygon

Question

I would like to determine a polygon and implement an algorithm which would check if a point is inside or outside the polygon.

Does anyone know if there is any exampl

Answer 1

I add one detail to help people who live in the... south of earth!! If you're in Brazil (that's my case), our GPS coord are all negatives. And all these algo give wrong results.

The easiest way if to use the absolute values of the Lat and Long of all point. And in that case Jan Kobersky's algo is perfect.