#include <cassert>
#include <iostream>
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Weffc++"
#pragma GCC diagnostic ignored "-Wunused-local-typedefs"
#pragma GCC diagnostic ignored "-Wunused-variable"
#include <boost/geometry.hpp>
#include <boost/geometry/geometries/point_xy.hpp>
#pragma GCC diagnostic pop
//Goal: determine if a polygon, derived from points, is convex
//Member function: if the convex_hull equals that points, it is convex
//
//Bug: convex_hull does make a convex polygon look concave for certain values
//
//Bug report is posted at https://svn.boost.org/trac/boost/ticket/9873
int main()
{
using namespace boost::geometry;
typedef model::d2::point_xy<double> Point;
typedef model::polygon<Point> Polygon;
//Example A: works as expected
{
/* Polygon used:
-
|
- 2---3
| |
- 1---0
|
+--|---|---|
(point values are those simplified from example B)
*/
const std::vector<Point> points {
{15.0,631.0},
{ 8.0,628.0},
{ 8.0,679.0},
{15.0,682.0}
};
Polygon polygon;
append(polygon, points);
assert(boost::geometry::num_points(polygon) == 4);
boost::geometry::correct(polygon);
assert(boost::geometry::num_points(polygon) == 5
&& "OK: boost::geometry::correct adds a point");
Polygon hull;
boost::geometry::convex_hull(polygon, hull);
assert(boost::geometry::num_points(hull) == 5
&& "OK: the hull of a convex polygon has the same number of points as that polygon");
assert(boost::geometry::equals(polygon,hull));
}
//Example B: does not work as expected
{
/* Polygon used:
-
|
- 2---3
| |
- 1---0
|
+--|---|---|
*/
const std::vector<Point> points {
{15.9835,631.923},
{8.24075,628.579},
{8.24075,679.58 },
{15.9835,682.926}
};
Polygon polygon;
append(polygon, points);
assert(boost::geometry::num_points(polygon) == 4);
boost::geometry::correct(polygon);
assert(boost::geometry::num_points(polygon) == 5
&& "OK: boost::geometry::correct adds a point");
Polygon hull;
boost::geometry::convex_hull(polygon, hull);
assert(boost::geometry::num_points(hull) == 6
&& "Should not add an extra point, as the original polygon was convex");
assert(!boost::geometry::equals(polygon,hull)
&& "Should be equal, but does not");
}
}
|
