along method

Point along(double distance)

Returns the Point at the distance (in meters) along the LineString. If the distance is greater than the length of the LineString, the last Point in the LineString will be returned. If the distance is less than 0, the first Point in the LineString will be returned.

Example:

LineString([Coordinate(1, 2), Coordinate(3, 4)]).along(100); // Point(Coordinate(2, 3))

Implementation

Point along(double distance) {
  if (distance <= 0) {
    return Point(coordinates.first);
  } else if (distance >= length) {
    return Point(coordinates.last);
  } else if (coordinates.length < 2) {
    return Point(coordinates.first);
  }

  if (coordinates.length > 2) {
    double distanceLeft = distance;
    for (int i = 0; i < coordinates.length - 1; i++) {
      final c1 = coordinates[i];
      final c2 = coordinates[i + 1];
      final segmentLength = c1.distanceTo(c2);
      if (distanceLeft <= segmentLength) {
        final ratio = distanceLeft / segmentLength;
        return Point(c1.interpolate(c2, ratio));
      } else {
        distanceLeft -= segmentLength;
      }
    }
  }

  final ratio = distance / length;
  return Point(coordinates.first.interpolate(coordinates.last, ratio));
}