CODEWITHSUNDEEP
c++boostboost-geometry
user1228633
user1228633

Reputation: 551

Create and check if point is inside polygon

I have a std::list of 2D points and would like to test if one point p lies inside the polygon given by the vector. I already found that boost::geometry has a function within to test this. Unfortunately I seem to use it in the wrong way:

void someFunction(...) {
    namespace bpl = boost::polygon;
    typedef bpl::polygon_data<double> Polygon;
    typedef bpl::polygon_traits<Polygon>::point_type Point;

    Polygon polygon;
    std::vector<Point> points;

    for (std::list<MyPointType>::const_iterator it = myPolygonPoints.begin(); it != myPolygonPoints.end(); ++it) {
        points.push_back(Point(it->GetX(),it->GetY()));
    } 

    polygon.set(points.begin(),points.end());
    // ...
    if (!boost::geometry::within(Point(someX,someY),polygon)) {
        doSomething();
    }
    //...
}

I get various compile errors, starting by unmatched types in the call of within. So what is the correct way to build a polygon and use it with within?

Greetings

Upvotes: 1

Views: 1729

Answers (2)

mr_georg
mr_georg

Reputation: 3713

Why not stick with the types that are given in the examples? See this page, for instance.

typedef boost::geometry::model::d2::point_xy<double> Point;
typedef boost::geometry::model::polygon<Point> Polygon;

For me it works then.

#include <boost/geometry.hpp>
#include <boost/geometry/geometries/point_xy.hpp>
#include <boost/geometry/geometries/polygon.hpp>
//...

Polygon poly;
//... construct the polygon

Point p(4, 1);

std::cout << "within: " << (boost::geometry::within(p, poly) ? "yes" : "no") << std::endl;

Upvotes: 1

lulyon
lulyon

Reputation: 7225

There is an example from http://www.boost.org/doc/libs/1_47_0/libs/geometry/doc/html/geometry/reference/algorithms/within/within_2.html

Based on what you mean, the code:

if (!boost::geometry::within(Point(someX,someY),polygon)) {
        doSomething();
}

should be:

Point point(someX,someY);
if (!boost::geometry::within(point,polygon)) {
        doSomething();
}

or:

   Point *ppoint = new point(someX,someY);
   if (!boost::geometry::within(*ppoint,polygon)) {
            doSomething();
   }

Because direct call for constructor Point(someX,someY) as a function without class instantiation is not allowed in C++.

Upvotes: 0

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