Re: [Boost-users] Default weight map doesn't work for weighted grid graph in A-star search

Subject: Re: [Boost-users] Default weight map doesn't work for weighted grid graph in A-star search
From: W.P. McNeill (billmcn_at_[hidden])
Date: 2010-06-30 19:25:23

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_at_[hidden]>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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