along function

Feature<Point> along(Feature<LineString> line, num distance, [ Unit unit = Unit.kilometers ])

Takes a line and returns a Point at a specified distance along the line.

If distance is less than 0, it will count distance along the line from end to start of line. If negative distance overshoots the length of the line, the start point of the line is returned. If distance is larger than line length, the end point is returned If line have no geometry or coordinates, an Exception is thrown

Implementation

Feature<Point> along(Feature<LineString> line, num distance,
    [Unit unit = Unit.kilometers]) {
  // Get Coords
  final coords = getCoords(line);
  if (coords.isEmpty) {
    throw Exception('line must contain at least one coordinate');
  }
  if (distance < 0) {
    distance = max(0, length(line, unit) + distance);
  }
  num travelled = 0;
  for (int i = 0; i < coords.length; i++) {
    if (distance >= travelled && i == coords.length - 1) {
      break;
    }
    if (travelled == distance) {
      return Feature<Point>(geometry: Point(coordinates: coords[i]));
    }
    if (travelled > distance) {
      final overshot = distance - travelled;
      final direction = bearing(Point(coordinates: coords[i]),
              Point(coordinates: coords[i - 1])) -
          180;
      final interpolated = destination(
        Point(coordinates: coords[i]),
        overshot,
        direction,
        unit,
      );
      return Feature<Point>(geometry: interpolated);
    } else {
      travelled += measure_distance.distance(Point(coordinates: coords[i]),
          Point(coordinates: coords[i + 1]), unit);
    }
  }
  return Feature<Point>(
      geometry: Point(coordinates: coords[coords.length - 1]));
}