Buffering linestring on right side creating weird results

[bertrandpellenard]

Hello,
I have a linestring and I am running the buffer function with an asymmetric distance. I want to buffer only on the right side of the linestring LINESTRING(0 0,-3 5,15 7,17 4,14 2)
I am getting unexpected results.

Here is an idea of the code:

using coordinate_type = double;
  using point = boost::geometry::model::d2::point_xy<coordinate_type>;
  using polygon = boost::geometry::model::polygon<point>;

  // Declare strategies
  const double buffer_distance = amount;
  const int points_per_circle = 36;
  boost::geometry::strategy::buffer::distance_symmetric<coordinate_type>
      bg_both_sides_distance_strategy(buffer_distance);

  boost::geometry::strategy::buffer::distance_asymmetric<coordinate_type>
      bg_left_side_distance_strategy(buffer_distance, 0.0);

  boost::geometry::strategy::buffer::distance_asymmetric<coordinate_type>
      bg_right_side_distance_strategy(0.0, buffer_distance);

  boost::geometry::strategy::buffer::join_miter bg_join_miter_strategy;
  boost::geometry::strategy::buffer::join_round bg_join_round_strategy(
      points_per_circle);

  boost::geometry::strategy::buffer::end_round bg_end_round_strategy(
      points_per_circle);

  boost::geometry::strategy::buffer::end_flat bg_end_flat_strategy;

  boost::geometry::strategy::buffer::point_circle bg_circle_strategy(
      points_per_circle);
  boost::geometry::strategy::buffer::side_straight bg_side_straight_strategy;

 // Declare output
  boost::geometry::model::multi_polygon<polygon> result;

 // Declare/fill a linestring
    boost::geometry::model::linestring<point> ls;
    ls.reserve(pts_in.size());
    for (const auto& pt : pts_in) {
      ls.emplace_back(pt[0], pt[1]);
    }

boost::geometry::buffer(ls, result, bg_right_side_distance_strategy,
                                  bg_side_straight_strategy,
                                  bg_join_round_strategy, bg_end_round_strategy,
                                  bg_circle_strategy);

std::cout << "output: " << boost::geometry::wkt(result) << std::endl;

Thank you.
Best regards.
Bertrand

[barendgehrels]

Thanks for the report. I can reproduce it. Also with different coordinates - so it's not a precision issue.
With a small left distance you see already some artefacts.

I cannot look at it right now, but will do later.

Adapted code:

    boost::geometry::strategy::buffer::distance_asymmetric<coordinate_type> bg_distance_strategy(0.025, 0.1);

and

    boost::geometry::model::linestring<point> ls;
    boost::geometry::read_wkt("LINESTRING(0 0,-3 5,15 7,17 4,14 2)", ls);

[bertrandpellenard]

I used boost::geometry::strategy::buffer::distance_asymmetric<coordinate_type> bg_distance_strategy(0.0, 1.0); in the pictures I shared