Check to see if a coordinate is within a given fence.

IsPointInPolygon.js

const fence = [
  [44.969886109093, -93.21685776103517],
  [44.98627907084557, -93.28243240703127],
  [44.9667284078666, -93.28208908427736],
  [44.93611398841498, -93.20192322124025],
  [44.93605322928645, -93.18498107787336],
  [44.956282465359436, -93.18510040629884],
];

// Outside of the fence
const point1 = [45.126606, -93.2065048]; 
console.log(isPointInFence(point1, fence)); // false

// On a fence point
const point2 = [44.9667284078666, -93.28208908427736];
console.log(isPointInFence(point2, fence)); // false

/*
Regarding Point 2:

If the test point is on the border of the polygon, this algorithm will deliver unpredictable results; i.e. the result may be 
“inside” or “outside” depending on arbitrary factors such as how the polygon is oriented with respect to the coordinate system. 
(That is not generally a problem, since the edge of the polygon is infinitely thin anyway, and points that fall right on the 
edge can go either way without hurting the look of the polygon.)
*/

// In the fence
const point3 = [44.9698, -93.2441];
console.log(isPointInFence(point3, fence)); // true

// Formula explination: http://alienryderflex.com/polygon/
// Adapted from: https://stackoverflow.com/a/42460157/5026438
function isPointInFence(point, fence) {
  // [y, x] = [latitude, longitude] 
  const [y, x] = point;
  let isInFence = false;

  for (let i = 0; i < (fence.length - 1); i++) {
    const [p1_y, p1_x] = fence[i];
    const [p2_y, p2_x] = fence[i + 1];

    if ((p1_y < y && p2_y >= y) || (p2_y < y && p1_y >= y)) { // this edge is crossing the horizontal ray of testpoint
      if ((p1_x + (y - p1_y) / (p2_y - p1_y) * (p2_x - p1_x)) < x) { // checking special cases (holes, self-crossings, self-overlapping, horizontal edges, etc.)
        isInFence = !isInFence;
      }
    }
  }

  return isInFence;
}