在使用cgal进行增量空间搜索时修改函子变量

Modifying functor variable when using incremental spatial searching with cgal

本文关键字：搜索 修改 变量 空间 cgal      更新时间：2023-10-16

我修改了计算几何cgal库给出的一个示例(链接)，该示例演示了在2D平面上的增量搜索(第49.3.2节)。这个例子使用一个函子来设置空间边界，以便只搜索平面上的正点。

我想修改函子，使k可以传入，如struct X_not_positive_k所示。下面的完整示例程序显示了修改后的代码和原始代码。

#include <CGAL/Simple_cartesian.h>
#include <CGAL/Orthogonal_incremental_neighbor_search.h>
#include <CGAL/Search_traits_2.h>
typedef CGAL::Simple_cartesian<double> K;
typedef K::Point_2 Point_d;
typedef CGAL::Search_traits_2<K> TreeTraits;
typedef CGAL::Orthogonal_incremental_neighbor_search<TreeTraits> NN_incremental_search;
typedef NN_incremental_search::iterator NN_iterator;
typedef NN_incremental_search::Tree Tree;
int main() {
    Tree tree;
    tree.insert(Point_d(0,0));
    tree.insert(Point_d(1,1));
    tree.insert(Point_d(0,1));
    tree.insert(Point_d(10,110));
    tree.insert(Point_d(45,0));
    tree.insert(Point_d(0,2340));
    tree.insert(Point_d(0,30));
    Point_d query(0,0);
    // A functor that returns true, iff the x-coordinate of a dD point is not positive
    // [ORIGINAL CODE]
    struct X_not_positive {
        bool operator()(const NN_iterator& it) { return ((*it).first)[0]<0;  }
    };
    // [MODIFIED CODE]
    // This does not work when used below.
    struct X_not_positive_k {
    public:
        void assign_k(int k) {this->k = k; }
        bool operator()(const NN_iterator& it) { return ((*it).first)[0] < k;  }
    private:
        int k;
    };
    X_not_positive_k Xk;
    Xk.assign_k(1);
    // An iterator that only enumerates dD points with positive x-coordinate
    // [ORIGINAL CODE]
    // typedef CGAL::Filter_iterator<NN_iterator, X_not_positive> NN_positive_x_iterator;
    // [MODIFIED CODE]
    typedef CGAL::Filter_iterator<NN_iterator, X_not_positive_k> NN_positive_x_iterator;
    NN_incremental_search NN(tree, query);
    // [ORIGINAL CODE]
    // NN_positive_x_iterator it(NN.end(), X_not_positive(), NN.begin()), end(NN.end(), X_not_positive());
    // [MODIFIED CODE]
    NN_positive_x_iterator it(NN.end(), Xk(), NN.begin()), end(NN.end(), Xk()); 
    // error occurs here
    std::cout <<  "The first 5 nearest neighbours with positive x-coord are: " << std::endl;
    for (int j=0; (j < 5)&&(it!=end); ++j,++it)
        std::cout <<   (*it).first << "  at squared distance = " << (*it).second << std::endl;
return 0;
}

但是，编译这个程序(Windows 7 with Visual Studio 2010)会导致以下编译错误。错误的位置在上面的代码中有标记。

2>..main.cpp(56): error C2064: term does not evaluate to a function taking 0 arguments
2>          class does not define an 'operator()' or a user defined conversion operator to a pointer-to-function or reference-to-function that takes appropriate number of arguments
2>..main.cpp(56): error C2064: term does not evaluate to a function taking 0 arguments
2>          class does not define an 'operator()' or a user defined conversion operator to a pointer-to-function or reference-to-function that takes appropriate number of arguments
2>

如何消除错误?是否有另一种方法可以设置k变量?

将Xk()替换为Xk

或者用构造函数参数替换assign(k)，然后替换Xk()与X_not_positive_k(1)

其实真正麻烦的是函子的名字!将名称X_not_positive_k替换为X_less_than -因此调用X_less_than(1)在第56行中看起来很好

: 

struct X_less_than {
public:
    X_less_than(int i)
      : k(i)
    {
    }
    bool operator()(const NN_iterator& it) { return ((*it).first)[0] < k;  }
private:
    int k;
};

你的错误在于

NN_positive_x_iterator it(.., X_not_positive(), .. )

X_not_positive是类型，X_not_positive()是构造函数的调用，

而在你的代码

NN_positive_x_iterator it(.., Xk(),.. )

Xk不是类型而是对象，Xk()是对operator()的调用这是零参数的函数操作符，因此出现错误消息。

andreas

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