(C++) BoostGeometryExample7

 

 

Boost.Geometry example 7: Bug in boost::geometry::convex_hull is a Boost.Geometry example.

Technical facts

 

Application type(s)

• Desktop application

Operating system(s) or programming environment(s)

• Lubuntu 15.04 (vivid)

IDE(s):

• Qt Creator 3.1.1

Project type:

• GUI application

C++ standard:

• C++11

Compiler(s):

• G++ 4.9.2

Libraries used:

• Qt: version 5.4.1 (32 bit)
• STL: GNU ISO C++ Library, version 4.9.2

 

 

 

 

 

Qt project file: ./CppBoostGeometryExample7/CppBoostGeometryExample7.pro

 

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exists(../../ConsoleApplication.pri) {   include(../../ConsoleApplication.pri) } !exists(../../ConsoleApplication.pri) {   QT += core   QT += gui   greaterThan(QT_MAJOR_VERSION, 4): QT += widgets   CONFIG   += console   CONFIG   -= app_bundle   TEMPLATE = app   CONFIG(release, debug|release) {     DEFINES += NDEBUG NTRACE_BILDERBIKKEL   }   QMAKE_CXXFLAGS += -std=c++11 -Wall -Wextra -Weffc++   unix {     QMAKE_CXXFLAGS += -Werror   } } exists(../../Libraries/Boost.pri) {   include(../../Libraries/Boost.pri) } !exists(../../Libraries/Boost.pri) {   win32 {     INCLUDEPATH += \       ../../Libraries/boost_1_55_0   } } SOURCES += main.cpp

 

 

 

 

 

./CppBoostGeometryExample7/main.cpp

 

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#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");   } }