
Geometry : 
Subject: Re: [geometry] intersection() gives nonconsistent results
From: Vicky Vergara (vicky_vergara_at_[hidden])
Date: 20190122 18:06:53
The following code is taken from the example on the documentation of
boost::geometry::intersection
I changed the polygons to be simple triangles that have one point in common.
#include <iostream>
#include <deque>
#include <boost/geometry.hpp>
#include <boost/geometry/geometries/point_xy.hpp>
#include <boost/geometry/geometries/polygon.hpp>
#include <boost/foreach.hpp>
int main()
{
typedef boost::geometry::model::polygon<boost::geometry::model::d2::point_xy<double> > polygon;
polygon green, blue;
boost::geometry::read_wkt("POLYGON((3 1,2 2,2 1,3 1))", green);
boost::geometry::read_wkt("POLYGON((2 3,2 2,1 2,2 3))", blue);
std::deque<polygon> output;
boost::geometry::intersection(green, blue, output);
int i = 0;
std::cout << "green && blue:" << std::endl;
BOOST_FOREACH(polygon const& p, output)
{
std::cout << i++ << ": " << boost::geometry::wkt(p) << std::endl;
}
return 0;
}
The Instresection its getting is
POLYGON((2 2,1 2,2 3,2 2))
Instead of a point.
My understanding is that his functions follows the OGC standard that says: Intersection (anotherGeometry: Geometry): Geometry — Returns a geometric object that represents the
Point set intersection of this geometric object with anotherGeometry.
Then the result should be POINT(2 2)
The spatial intersection of 2 polygons can be a collection of multi geometries
Sometimes the intersection can be an Area
Sometimes the intersection can be a linestrig
Sometimes the intersection can be one point
Sometimes the intersection can be a collection of geometries that have an area, linestring and a point
What type do I have to make
std::deque<polygon> output;
in order to get either a polygon, a linestring or a point or a collection of anything?
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