Vsevolod Kamenovsky

Кому интересно, переписал класс с c++ на php.
Этот код https://github.com/VladimirBalun/Algorithms/blob/m...
Объяснение в этой статье https://habr.com/ru/post/448618/

class RamerDuglasPeucker
{

  /* @var Monitoring $start_point */
  /* @var Monitoring $end_point */
  /* @var Monitoring $point */

  private static function get_distance_between_point_and_line_segment($start_point, $end_point, $point)
  {
    // тут мои кастомные методы (getLatitude, getLongitude). Можно заменить их на ['lat'], ['long']
    $x = $point->getLatitude(); 
    $y = $point->getLongitude();

    $x1 = $start_point->getLatitude();
    $y1 = $start_point->getLongitude();

    $x2 = $end_point->getLatitude();
    $y2 = $end_point->getLongitude();

    $double_area = abs(($y2 - $y1) * $x - ($x2 - $x1) * $y + $x2 * $y1 - $y2 * $x1);
    $line_segment_length = sqrt(pow(($x2 - $x1), 2) + pow(($y2 - $y1), 2));
    if ($line_segment_length != 0)
      return $double_area / $line_segment_length;
    else
      return 0;
  }

  private static function simplify_points(array $src_points, array &$dest_points, float $tolerance, int $begin, int $end)
  {
    if ($begin + 1 == $end)
      return;

    $max_distance = -1;
    $max_index = 0;
    for ($i = $begin + 1; $i < $end; $i++) {
      $cur_point = $src_points[$i];
      $start_point = $src_points[$begin];
      $end_point = $src_points[$end];
      $distance = RamerDuglasPeucker::get_distance_between_point_and_line_segment($start_point, $end_point, $cur_point);

      if ($distance > $max_distance) {
        $max_distance = $distance;
        $max_index = $i;
      }
    }

    if ($max_distance > $tolerance) {
      RamerDuglasPeucker::simplify_points($src_points, $dest_points, $tolerance, $begin, $max_index);
      $dest_points[] = $src_points[$max_index];
      RamerDuglasPeucker::simplify_points($src_points, $dest_points, $tolerance, $max_index, $end);
    }
  }

  public static function downsample(array &$src_points, float $tolerance)
  {
    if ($tolerance <= 0)
      return $src_points;

    $dest_points = [];
    $dest_points[] = reset($src_points);
    RamerDuglasPeucker::simplify_points($src_points, $dest_points, $tolerance, 0, count($src_points) - 1);
    $dest_points[] = end($src_points);
    return $dest_points;
  }
}