How do I use an explicit weight map?  I thought specializing property_map<> would be the preferred way to add edge weights to a graph that doesn't already contain them.

BTW, here is the entire spew up to the first error message:

g++ -g -I/opt/local/include   -c -o main.o main.cpp
/opt/local/include/boost/iterator/transform_iterator.hpp: In constructor ‘boost::transform_iterator<UnaryFunction, Iterator, Reference, Value>::transform_iterator() [with UnaryFunc = boost::detail::grid_graph_vertex_at<boost::grid_graph<2ul, size_t, size_t> >, Iterator = boost::counting_iterator<size_t, boost::use_default, boost::use_default>, Reference = boost::use_default, Value = boost::use_default]’:
/opt/local/include/boost/graph/astar_search.hpp:285:   instantiated from ‘void boost::astar_search(VertexListGraph&, typename boost::graph_traits<G>::vertex_descriptor, AStarHeuristic, AStarVisitor, PredecessorMap, CostMap, DistanceMap, WeightMap, VertexIndexMap, ColorMap, CompareFunction, CombineFunction, CostInf, CostZero) [with VertexListGraph = boost::grid_graph<2ul, size_t, size_t>, AStarHeuristic = boost::euclidean_heuristic, AStarVisitor = boost::astar_goal_visitor, PredecessorMap = boost::dummy_property_map, CostMap = boost::vector_property_map<float, boost::grid_graph_index_map<boost::grid_graph<2ul, size_t, size_t>, boost::array<size_t, 2ul>, size_t> >, DistanceMap = boost::vector_property_map<float, boost::grid_graph_index_map<boost::grid_graph<2ul, size_t, size_t>, boost::array<size_t, 2ul>, size_t> >, WeightMap = boost::edge_weight_map, VertexIndexMap = boost::grid_graph_index_map<boost::grid_graph<2ul, size_t, size_t>, boost::array<size_t, 2ul>, size_t>, ColorMap = boost::vector_property_map<boost::default_color_type, boost::grid_graph_index_map<boost::grid_graph<2ul, size_t, size_t>, boost::array<size_t, 2ul>, size_t> >, CompareFunction = std::less<float>, CombineFunction = boost::closed_plus<float>, CostInf = float, CostZero = float]’
/opt/local/include/boost/graph/astar_search.hpp:318:   instantiated from ‘void boost::detail::astar_dispatch2(VertexListGraph&, typename boost::graph_traits<G>::vertex_descriptor, AStarHeuristic, CostMap, DistanceMap, WeightMap, IndexMap, ColorMap, const Params&) [with VertexListGraph = boost::grid_graph<2ul, size_t, size_t>, AStarHeuristic = boost::euclidean_heuristic, CostMap = boost::vector_property_map<float, boost::grid_graph_index_map<boost::grid_graph<2ul, size_t, size_t>, boost::array<size_t, 2ul>, size_t> >, DistanceMap = boost::vector_property_map<float, boost::grid_graph_index_map<boost::grid_graph<2ul, size_t, size_t>, boost::array<size_t, 2ul>, size_t> >, WeightMap = boost::edge_weight_map, IndexMap = boost::grid_graph_index_map<boost::grid_graph<2ul, size_t, size_t>, boost::array<size_t, 2ul>, size_t>, ColorMap = boost::vector_property_map<boost::default_color_type, boost::grid_graph_index_map<boost::grid_graph<2ul, size_t, size_t>, boost::array<size_t, 2ul>, size_t> >, Params = boost::bgl_named_params<boost::astar_goal_visitor, boost::graph_visitor_t, boost::no_property>]’
/opt/local/include/boost/graph/astar_search.hpp:350:   instantiated from ‘void boost::detail::astar_dispatch1(VertexListGraph&, typename boost::graph_traits<G>::vertex_descriptor, AStarHeuristic, CostMap, DistanceMap, WeightMap, IndexMap, ColorMap, const Params&) [with VertexListGraph = boost::grid_graph<2ul, size_t, size_t>, AStarHeuristic = boost::euclidean_heuristic, CostMap = boost::detail::error_property_not_found, DistanceMap = boost::detail::error_property_not_found, WeightMap = boost::edge_weight_map, IndexMap = boost::grid_graph_index_map<boost::grid_graph<2ul, size_t, size_t>, boost::array<size_t, 2ul>, size_t>, ColorMap = boost::detail::error_property_not_found, Params = boost::bgl_named_params<boost::astar_goal_visitor, boost::graph_visitor_t, boost::no_property>]’
/opt/local/include/boost/graph/astar_search.hpp:372:   instantiated from ‘void 

On Wed, Jun 30, 2010 at 4:09 PM, Jeremiah Willcock <jewillco@osl.iu.edu> wrote:
On Wed, 30 Jun 2010, W.P. McNeill wrote:

I am trying to write a simple example of an a-star search over a 2-dimensional grid using the Boost Graph Library.  The source is hosted
here: http://github.com/wpm/Boost-Searchable-Grid-Example.  My intent is for this to be a resource for other people writing a-star searches.
I am seeing an error about a missing weight map when I try to compile the call to astar_search().  As far as I can tell, everything is in order.  I hoping someone
has insight into what I'm missing.

My graph class is a rank-2 grid graph called weighted_grid defined like so:

  typedef grid_graph<2> weighted_grid;

I have a simple map that returns a weight of zero for every edge.

  struct edge_weight_map {
    typedef float value_type;
    typedef float reference;
    typedef edge_descriptor key_type;
    typedef readable_property_map_tag category;

    reference operator[](key_type e) const {
      // All edges have a weight of zero.
      return 0;
    }
  };

I associate this map with the weighted_grid class by specializing property_map.

  template<>
  struct property_map<weighted_grid,
                      edge_weight_t> {
    typedef edge_weight_map type;
    typedef edge_weight_map const_type;
  };

Since you didn't write the grid_graph class, this is not the correct way to add property maps.  You will need to use an external property map (such as iterator_property_map) as your weight map, and then pass it in explicitly to the astar_search() function.


I've defined valid expression functions for this property map along with a Euclidean distance heuristic and a visitor that throws an exception when a goal vertex is reached.  The complete source is viewable at the URL given above.

With these definitions I can do concept checks on the ReadablePropertyMap, ReadablePropertyGraph, VertexListGraph, and AStarHeuristic concepts.  I can instantiate a weighted_grid.  I can get the edge weight map using get(edge_weight, g) and the vertex index map using get(vertex_index, g).  I think I have written everything I need to do a-star search.

However, the following call does not build:

  vertex_descriptor source = vertex(0, g), goal = vertex(3, g);
  astar_search(g,
               source,
               euclidean_heuristic(goal),
               visitor(astar_goal_visitor(goal)) );

I get a long error spew.  The first relevant problem appears to be here:

The error here doesn't have enough of the instantiation stack to be useful.  Just use an explicit weight map, though, and that is more likely to work.

-- Jeremiah Willcock
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