Geo-Zone Determination (Point in Polygon)

I use this in my app to determine if a vehicle is within a defined zone made of 5 or more lat/lon coordinates. Point 1 is also Point 5 (first point and last point are same value).
A simple box shows how to create this:

1----------2
| ........... |
| ........... | clockwise (or counter clockwise)
| ........... |
4----------3

In my case, I determine either a) the speed of the vehicle or b) how long stopped in zone.

Note: Larger zones work best due to the inaccuracy of GPS. My accuracy...

Geo-Zone Determination (Point in Polygon)

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