Function joinAllWithBuffer

src/utilities/geometry/Intersection.cpp:1557–1633

buffers the polygons to increase reliability of joining

// buffers the polygons to increase reliability of joining
std::vector<std::vector<Point3d>> joinAllWithBuffer(const std::vector<std::vector<Point3d>>& polygons, double offset, double tol) {
  std::vector<std::vector<Point3d>> result;

  const size_t N = polygons.size();
  if (N <= 1) {
    return polygons;
  }

  std::vector<double> polygonAreas(N, 0.0);
  for (unsigned i = 0; i < N; ++i) {
    auto area = getArea(polygons[i]);
    if (area) {
      polygonAreas[i] = *area;
    }
  }

  std::vector<std::vector<Point3d>> modifiedPolygons;

  for (unsigned i = 0; i < N; i++) {
    modifiedPolygons.push_back(*buffer(polygons[i], offset, tol));
  }

  // compute adjacency matrix
  Matrix A(N, N, 0.0);
  for (unsigned i = 0; i < N; ++i) {
    A(i, i) = 1.0;
    for (unsigned j = i + 1; j < N; ++j) {
      if (join(modifiedPolygons[i], modifiedPolygons[j], tol)) {
        A(i, j) = 1.0;
        A(j, i) = 1.0;
      }
    }
  }

  const std::vector<std::vector<unsigned>> connectedComponents = findConnectedComponents(A);
  for (const std::vector<unsigned>& component : connectedComponents) {
    std::vector<unsigned> orderedComponent(component);
    std::sort(orderedComponent.begin(), orderedComponent.end(), [&polygonAreas](int ia, int ib) { return polygonAreas[ia] > polygonAreas[ib]; });

    std::vector<Point3d> points;
    std::set<unsigned> joinedComponents;

    // try to join at most component.size() times
    for (unsigned n = 0; n < component.size(); ++n) {

      // loop over polygons to join in order
      for (const unsigned i : orderedComponent) {
        if (points.empty()) {
          points = modifiedPolygons[i];
          joinedComponents.insert(i);
        } else {
          // if not already joined
          if (joinedComponents.find(i) == joinedComponents.end()) {
            boost::optional<std::vector<Point3d>> joined = join(points, modifiedPolygons[i], tol);
            if (joined) {
              points = *joined;
              joinedComponents.insert(i);
            }