
Geometry : 
Subject: Re: [geometry] Why closure?
From: Mateusz Loskot (mateusz_at_[hidden])
Date: 20130620 07:42:16
On 20 June 2013 10:26, TONGARI <tongari95_at_[hidden]> wrote:
>
> I'm not quite understand why we need traits::closure for Ring & Polygon,
> aren't these always closed?
You can define open polygon or ring, means
typedef bg::model::polygon<point, false, false> polygon; // open polygon
typedef bg::model::ring<point, false, false> ring; // open ring
where the following condition does not hold
last point == first point
It is specification of the fact if first point is assumed as repeated or not
at last position.
> What should I expect if the closure is open?
Algorithms won't expect physical presence of the repeated first point.
> Should I see Ring as Linestring
Ring is also known as linear ring, in case you know OGC geometry model.
IOW, (linear) ring is a specialisation of the linestring kind.
Best regards,
 Mateusz Loskot, http://mateusz.loskot.net
Geometry list run by mateusz at loskot.net