BGL：用數據獲取頂點描述符

Question

我想用頂點的合成器獲取頂點描述符，如下所示：

struct WayPoint{
std::pair<float, float> pos; // with this composant
};

附件清單：

typedef boost::adjacency_list<  
    boost::listS,              
    boost::vecS,                
    boost::undirectedS,         
    WayPoint,                   
    WayPointConnection          
> WayPointGraph;
typedef WayPointGraph::vertex_descriptor WayPointID;
typedef WayPointGraph::edge_descriptor   WayPointConnectionID;

我構建了我的圖形並創建了所有頂點/邊......目的是在圖上應用astar。

void PathFinding::findMeAPath(std::pair<float, float>begin, std::pair<float, float>end)
{
    std::vector<WayPointID> p(boost::num_vertices(graphe)); 
    std::vector<float>      d(boost::num_vertices(graphe)); 
    WayPointID start = // I want to find the WayPointID with begin
    WayPointID goal = //same with end;
    shortest_path.clear();
    try {
        boost::astar_search
        (
        graphe, 
        start,  
        boost::astar_heuristic<WayPointGraph, float>(), 
        boost::predecessor_map(&p[0]).distance_map(&d[0]).visitor(astar_goal_visitor(goal)).weight_map(boost::get(&WayPointConnection::dist, graphe))
        );

    } catch(found_goal fg) { 

    for(WayPointID v = goal;; v = p[v]) {
        shortest_path.push_front(v);
        if(p[v] == v)
            break;
    }
    }
  }

Answer 1

您需要編寫一個函數來查找給定位置的頂點。 您定義的圖形類型使用std :: vector來存儲頂點，因此函數必須迭代它並將查詢的位置與每個WayPoint進行比較。 像這樣的東西可以做：

std::pair<WayPointID, bool> find_vertex(const WayPoint& wp, const WayPointGraph& graph)
{
  for (WayPointID id = 0; id < boost::num_vertices(graph); ++id)
  {
    if (equal(graph[id], wp))
      return std::make_pair(id, true);
  }
  return std::make_pair(0, false);
}

請注意，該函數返回一對（Id +布爾標志）以指示搜索是否成功，因此您將按如下方式使用它：

bool vertex_found;
WayPointID start;
std::tie (start, vertex_found) = find_vertex(begin, graphe);
if (!vertex_found)
  // do something about it

此功能還使用以下內容來比較位置：

bool equal(const std::pair<float, float>& p1, const std::pair<float, float>& p2)
{
  const float EPS = 1e-6;
  return (std::fabs(p1.first - p2.first) < EPS &&
          std::fabs(p1.second - p2.second) < EPS);
}