如何使用boost::uniform_on_sphere？

Question

我试图在单位球面上选取一个随机点，并发现boost提供的分布正是这样做的。但是当我尝试使用它时，所有生成的值都是nan。我不知道我做错了什么，你能告诉我吗？这段小代码描述了我正在尝试做的事情：

#include <iostream>
#include <fstream>
#include <vector>
#include <boost/random/mersenne_twister.hpp>
#include <boost/random/uniform_on_sphere.hpp>

int main()
{
  boost::mt19937 gen;
  boost::uniform_on_sphere<float> dist(3);

  { // Seed from system random device
    std::ifstream rand_device("/dev/urandom");
    uint32_t seed;
    rand_device >> seed;

    gen.seed(seed);
  }

  while(1) {
    // Generate a point on a unit sphere
    std::vector<float> res = dist(gen);

    // Print the coordinates
    for(int i = 0; i < res.size(); ++i) {
      std::cout << res[i] << ' ';
    }
    std::cout << '\n';
  }
}

输出为：

nan nan nan 
nan nan nan 
nan nan nan 
nan nan nan 

无穷无尽。

Answer 1

我假设你使用的是Boost 1.49。下面的方法适用于这种情况。

这就是Boost有点复杂的地方。uniform_on_sphere对象只是绘制点所需的组件之一，它是分布部分。您还需要按照下面的工作.cpp文件创建一个boost::variate_generator。

注意，这有我自己的包含使用系统时间来播种，等等。你应该能够修改它，以适合你。

// Standards, w/ctime to seed based on system time.
#include <iostream>
#include <fstream>
#include <vector>
#include <ctime>

// Boost. Requires variate_generator to actually draw the values.
#include <boost/random/mersenne_twister.hpp>
#include <boost/random/uniform_on_sphere.hpp>
#include <boost/random/variate_generator.hpp>


int main(){

    typedef boost::random::mt19937 gen_type;

    // You can seed this your way as well, but this is my quick and dirty way.
    gen_type rand_gen;
    rand_gen.seed(static_cast<unsigned int>(std::time(0)));

    // Create the distribution object.
    boost::uniform_on_sphere<float> unif_sphere(3);

    // This is what will actually supply drawn values.
    boost::variate_generator<gen_type&, boost::uniform_on_sphere<float> >    random_on_sphere(rand_gen, unif_sphere);

    // Now you can draw a vector of drawn coordinates as such:
    std::vector<float> random_sphere_point = random_on_sphere();

    // Print out the drawn sphere triple's values.
    for(int i = 0; i < random_sphere_point.size(); ++i) {
        std::cout << random_sphere_point.at(i) << ' ';
    }
    std::cout << '\n';

    return 0;
}

当我在控制台中运行它时，我得到了看似正确的东西：

ely@AMDESK:~/Desktop/Programming/C++/RandOnSphere$ g++ -I /usr/include/boost_1_49/ -L    /usr/include/boost_1_49/stage/lib randomOnSphere.cpp -o ros
ely@AMDESK:~/Desktop/Programming/C++/RandOnSphere$ ./ros 
0.876326 -0.0441729 0.479689 
ely@AMDESK:~/Desktop/Programming/C++/RandOnSphere$ ./ros 
-0.039037 -0.17792 0.98327 
ely@AMDESK:~/Desktop/Programming/C++/RandOnSphere$ ./ros 
-0.896734 0.419589 -0.14076