CGAL users discussion list

[Rolf van der Hulst <>]

Hi Efi,

Thanks for your help. I wrote a similar function (using a different approach) myself already, but good to know that there is no library functionality to do this.
Then you can consider my email as a suggestion that such a function could be added to CGAL :)

Best,
Rolf

On 21-12-2022 15:49, Efi Fogel ( via cgal-discuss Mailing List) wrote:

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Hi Rolf,

I don't think that there is a function that splits the boundary of a polygon with holes into simple polygons, but you can do something like the following (untested code):

Construct a Polygon_set_2 object.

Polygon_set_2 ps;

Update it; that is, apply Boolean operations.

Extract the underlying arrangement:

const auto& arrangement = ps.arrangement();

Traverse the arrangement faces; discard faces that are not part of the result; something like the following:

for (auto fh : arrangement.faces_handles()) {

  if (! fh->contained() continue;

  auto ccb = fh->outer_ccb();

  typename Arrangement::Halfedge_const_handle he = ccb;

  do std::cout << he->target()->point() << " ";
  while (++he != ccb);
  std::cout << std::endl;

  // Traverse the outer ccb of the face

}

Efi

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  /_____/_) o    /__________  __  //
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                         _/

On Tue, 13 Dec 2022 at 12:59, Rolf van der Hulst <> wrote:

Hi,

The CGAL manual for 2d-regularized polygon operations states that as requirements on its output that CGAL::Polygon_with_holes_2 must be a relatively simple polygon, e.g. a polygon where vertices may have degree >2, but with non-intersecting edges. Now suppose that the polygon with holes I have has no holes, then if it is relatively simple but not simple, it is actually a set of simple polygons touching eachother in a few points.

Is there an algorithm in CGAL which can convert the relatively simple polygons given by 2d set operations into a vector of simple polygons? I could not find any, but it seems like important functionality, so I may have overlooked something. I could probably write my own, but I'd rather use a more robust library feature if possible.

Best,

Rolf van der Hulst

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