Simplify a line (using Ramer-Douglas-Peucker algorithm).

rdp-simplify.ts

/**
 * Simplify a line (using Ramer-Douglas-Peucker algorithm).
 * @param points An array of points as [x, y, ...][]
 * @param tolerance The minimum line distance (also called epsilon).
 * @returns Simplified array as [x, y, ...][]
 */
export function simplify(points: number[][], tolerance = 1) {
  const len = points.length,
    a = points[0],
    b = points[len - 1],
    [x1, y1] = a,
    [x2, y2] = b

  if (len > 2) {
    let distance = 0,
      index = 0,
      max = Math.hypot(y2 - y1, x2 - x1)

    for (let i = 1; i < len - 1; i++) {
      const [x0, y0] = points[i],
        d = Math.abs((y2 - y1) * x0 - (x2 - x1) * y0 + x2 * y1 - y2 * x1) / max

      if (distance > d) continue

      distance = d
      index = i
    }

    if (distance > tolerance) {
      let l0 = simplify(points.slice(0, index + 1), tolerance)
      let l1 = simplify(points.slice(index + 1), tolerance)
      return l0.concat(l1.slice(1))
    }
  }

  return [a, b]
}