Augment custom weights to edge descriptors in boost::grid_graph

Question

I am using BGL for a custom AStar search. Basically, the nodes of the graph correspond to the cells of a map, and each cell has an elevation.

I've created an cell traversal score function stepTime which takes in the elevation of two cells, and outputs a cost function. I wanna add this cost function to the edge weights in my boost graph.

How do I go about this? I've seen functions using

auto weightmap = make_transform_value_property_map

to create a weight map, but how do I update the weights according to the output of:

double stepTime(const vertex_descriptor& source, const vertex_descriptor& target, const std::vector<uint8_t>& elevation)

Answer 1

but how do I update the weights according to the output of:

 double stepTime(const vertex_descriptor& source, const vertex_descriptor& target, const std::vector<uint8_t>& elevation)

I have no clue where you get the elevation vector from, but I guess that's your problem.

The source and target vertices are easily gotten from the graph itself, so here goes:

auto custom = boost::make_function_property_map<Graph::edge_descriptor>(
        [&g,&elevation](Graph::edge_descriptor e) {
            return stepTime(boost::source(e, g), boost::target(e, g), elevation);
        });

Demo

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#include <boost/graph/adjacency_list.hpp>
#include <boost/graph/astar_search.hpp>
#include <boost/property_map/function_property_map.hpp>
#include <iostream>

using Graph = boost::adjacency_list<>;

double stepTime(const Graph::vertex_descriptor& source, const Graph::vertex_descriptor& target, const std::vector<uint8_t>& elevation) {
    std::cout << __FUNCTION__ << "(" << source << ", " << target << ", {" << elevation.size() << " elements})\n";
    return 42;
}

int main() {
    Graph g(10);
    add_edge(4, 5, g);
    add_edge(2, 8, g);
    add_edge(5, 1, g);
    add_edge(1, 3, g);

    std::vector<uint8_t> const elevation { 1,2,3,4,5,6 }; // or whatevs

    // custom weight map
    auto custom = boost::make_function_property_map<Graph::edge_descriptor>(
            [&g,&elevation](Graph::edge_descriptor e) {
                return stepTime(boost::source(e, g), boost::target(e, g), elevation);
            });

    // pass it to an algorithm directly, or wrap it in a named-parameter object:
    auto param = boost::weight_map(custom);
    param.weight_map2(custom); // or as the alternative weight map
}