CGAL users discussion list

["Sebastien Loriot (GeometryFactory)" <>]

The first thing to do is to compute snap rounded version of your
polygons and then process them. You will avoid degenerate cases handling.
I have no idea what is the expected output but your either use a
Constrained Delaunay Triangulation or an arrangement to compute one.

Relevant documentation pages:

http://www.cgal.org/Manual/latest/doc_html/cgal_manual/Triangulation_2/Chapter_main.html#Section_36.8
http://www.cgal.org/Manual/latest/doc_html/cgal_manual/Snap_rounding_2/Chapter_main.html
http://www.cgal.org/Manual/latest/doc_html/cgal_manual/Arrangement_on_surface_2/Chapter_main.html

Sebastien.

Graviton wrote:
> I have a lot of polygons. Ideally, all the polygons must not overlap one
> other, but they can be located adjacent to one another. You can assume that
> these polygons represent countries on a map, and I import these polygons
> from a drawing. Due to rounding errors, I would have to allow for slight
> polygon overlap ( defined by a certain tolerance) because all these polygons
> are obtained from user hand drawing input, which is not as machine-precised
> as I want them to be. 
>
> My question is how to convert these polygons into mesh ( with vertexes and
> faces) and at the same time, one still knows which face it belongs to in the
> original polygon. Any idea how to proceed with this?
>
> My current idea is that I would
>
> 1. create one arrangement for each polygon ( a country), tag the faces in
> the arrangement, see whether it is an unbounded face, or a bounded one. So
> that each bounded face, I can still keep track it back to the original
> polygon ( a country)
> 2. overlay all the arrangement together, and obtain an arrangement. Inside
> this arrangement there will be a lot of faces, some of the faces are
> correctly belonged to the only 1 face, some of the face is a result of two
> polygon slightly overlapped one another. 
> 3. After obtaining the faces, I will use snap rounding to clear off all the
> sliver (http://en.mimi.hu/gis/sliver_polygon.html) and maybe eliminate a few
> of the faces resulting from two polygon overlapped one another. This should
> properly clean up the topology
> 4. Now all the polygons are in proper topology, i.e, no more sliver, no more
> overlapped polygon, I can then collect the points and the face to construct
> a mesh.
>
> What do you think about the above approach? Or is there any other more
> direct way of doing things?
>
> This is a SO post, asking about the same thing.
> http://stackoverflow.com/questions/7495487/convert-polygons-into-mesh
>
>
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