GPS Location?

/*
 * Free to use as you see fit. 
 */

package GPS

type polygon [][]float64

// Enter the lat,long coordinates (min 3)
// poly := [][]float64{ { 1,1 }, { 1,2 }, { 2,2 }, { 2,1 } ... {1,1}}
// Make sure the polygon coordinates are specified in the correct order,
// typically in a counter-clockwise direction, and that the last vertex is
// the same as the first one to close the polygon.
// in := inside(1.5, 1.5, poly) --> True
// in := inside(2.5, 1.5, poly) --> False

// Test if a GPS coordinate is inside the bounding box
func Inside(latitude float64, longitude float64, boundary polygon) bool {
    inside := false

    j := len(boundary) - 1
    for i := 0; i < len(boundary); i++ {

       xi := boundary[i][0]
       yi := boundary[i][1]

       xj := boundary[j][0]
       yj := boundary[j][1]

       // Crossing the border of the polygon?
       intersect := ((yi > latitude) != (yj > latitude)) && 
                    (longitude < (xj-xi)*(latitude-yi)/(yj-yi)+xi)

       if intersect {
          inside = !inside
       }
       j = i
    }

    return inside
}