Geometry Boost List: Re: [geometry] Ring intersection question

Subject: Re: [geometry] Ring intersection question
From: Barend Gehrels (barend_at_[hidden])
Date: 2014-11-07 04:06:49

Hi Adam,

Adam Wulkiewicz wrote On 7-11-2014 0:33:
> Hi,
>
> Menelaos Karavelas wrote:
>> On 07/11/2014 12:10 ??, Menelaos Karavelas wrote:
>>> On 06/11/2014 11:56 ??, Will Lucas wrote:
>>>
>>>> This would hopefully allow me to define a custom multi_polygon. As 
>>>> my initial attempt to just create an std::vector<dft::Contour> as a 
>>>> multi_polygon, resulted in a bunch of compiler complaints :D
>>>>
>>>
>>> I think this is because your vector's value type is a ring rather 
>>> than a polygon.
>
> Actually this works for me. Though since a container of Rings isn't a 
> "proper" Geometry other functions may not work with it, e.g. bg::wkt() 
> from your example.
> My code:
>
> #include<boost/foreach.hpp>
> #include  <boost/geometry.hpp>
> namespace  bg  =  boost::geometry;
> typedef  bg::model::point<int,  2,  bg::cs::cartesian>  point_type;
> typedef  bg::model::ring<point_type>  ring_type;
> typedef  std::vector<ring_type>  rings_container;
> int  main()
> {
>      ring_type  pol1,  pol2;
>      bg::read_wkt("POLYGON((75  75,75  175,275  175,275  75,75  75))",  pol1);
>      bg::read_wkt("POLYGON((50  50,50  150,250  150,250  50,50  50))",  pol2);
>      rings_container  rings;
>      bg::intersection(pol1,  pol2,  rings);
>      BOOST_FOREACH(ring_type  const&  r,  rings)
>          std::cout  <<  bg::wkt(r)  <<  std::endl;
>      return  0;
> }
> FYI, it compiles also if the input Geometries are Polygons. I tried this:
>
> polygon_typepol1,pol2;
> bg::read_wkt("POLYGON((0  0,0  10,10  10,10  0,0  0),(4  4,6  4,6  6,4  6,4  4))",  pol1);
> bg::read_wkt("POLYGON((1  1,1  11,11  11,11  1,1  1))",  pol2);
> rings_container  rings;
> bg::intersection(pol1,  pol2,  rings);
> BOOST_FOREACH(ring_type  const&  r,  rings)
>      std::cout  <<  bg::wkt(r)  <<  std::endl;
> bg::intersection(pol2,  pol1,  rings);
> BOOST_FOREACH(ring_type  const&  r,  rings)
>      std::cout  <<  bg::wkt(r)  <<  std::endl;
>
> In this case holes aren't included in the output:
>
> POLYGON((1 10,10 10,10 1,1 1,1 10))
> POLYGON((1 10,10 10,10 1,1 1,1 10))
>
> Is this behavior intended?

Yes, it is. Holes are skipped for rings. There are also unit tests for this.

Regards, Barend