feat: add biconnected_components instead of isolated

CMakeLists.txt

@@ -44,6 +44,8 @@ target_link_libraries(boost_geometry
     Boost::type_traits
     Boost::utility
     Boost::variant
+
+    Boost::graph
 )
 
 # Required for Boost.Geometry Index
@@ -112,7 +114,10 @@ if(BUILD_TESTING AND EXISTS "${CMAKE_CURRENT_SOURCE_DIR}/test/CMakeLists.txt")
           serialization
           tokenizer
           variant
-          test)
+          test
+
+          graph
+          )
 
     if (BOOST_SRC_DIR_IS_VALID)
       set(BOOST_EXCLUDE_LIBRARIES ${PROJECT_NAME})

include/boost/geometry/algorithms/detail/overlay/detect_biconnected_components.hpp

@@ -0,0 +1,227 @@
+// Boost.Geometry
+
+// Copyright (c) 2024 Barend Gehrels, Amsterdam, the Netherlands.
+
+// Use, modification and distribution is subject to the Boost Software License,
+// Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+
+#ifndef BOOST_GEOMETRY_ALGORITHMS_DETAIL_OVERLAY_DETECT_ARTICULATION_POINTS_HPP
+#define BOOST_GEOMETRY_ALGORITHMS_DETAIL_OVERLAY_DETECT_ARTICULATION_POINTS_HPP
+
+#include <map>
+#include <set>
+
+#include <boost/geometry/algorithms/detail/overlay/segment_identifier.hpp>
+#include <boost/geometry/algorithms/detail/overlay/node_util.hpp>
+#include <boost/geometry/algorithms/detail/overlay/graph_util.hpp>
+
+#include <boost/graph/biconnected_components.hpp>
+#include <boost/graph/adjacency_list.hpp>
+
+namespace boost { namespace geometry
+{
+
+#ifndef DOXYGEN_NO_DETAIL
+namespace detail { namespace overlay
+{
+
+
+struct vertex_info
+{
+    signed_size_type node_id{0};
+    std::set<std::size_t> target_vertex_indices;
+
+    bool is_extra{false};
+
+    // For extra nodes, also store the original node
+    signed_size_type original_node_id{0};
+};
+
+struct state_type
+{
+    // Maps from vertex to vertex info
+    std::map<std::size_t, vertex_info> vertex_map;
+
+    // Reverse mapping. Every node (turn or cluster) has only ONE vertex,
+    // but there might be additional vertices, not associated with a node.
+    std::map<signed_size_type, std::size_t> node_to_vertex_index;
+
+    // Keeps track of vertex index, which must, for Boost.Graph,
+    // be consecutive. The turn index is not (because of discarded and clusters).
+    std::size_t vertex_index{0};
+
+    // For some cases (returning to itself) extra nodes are inserted.
+    // They are numbered from turn.size() and up.
+    std::size_t extra_node_id{0};
+};
+
+void add_target_node(signed_size_type source_node_id, signed_size_type target_node_id,
+                     state_type& state, bool allow_returning)
+{
+    // Insert the source and target node (turn or cluster)
+    auto it_source = state.node_to_vertex_index.find(source_node_id);
+    if (it_source == state.node_to_vertex_index.end())
+    {
+        it_source = state.node_to_vertex_index.insert({source_node_id, state.vertex_index++}).first;
+    }
+
+    auto it_target = state.node_to_vertex_index.find(target_node_id);
+    if (it_target == state.node_to_vertex_index.end())
+    {
+        it_target = state.node_to_vertex_index.insert({target_node_id, state.vertex_index++}).first;
+    }
+
+    // Get the accompanying vertex into (might be a new record)
+    auto& vertex_info = state.vertex_map[it_source->second];
+    vertex_info.node_id = source_node_id;
+
+    if (target_node_id == source_node_id && allow_returning)
+    {
+        std::size_t const extra_node_id = state.extra_node_id++;
+
+        // Add a brand new vertex, and add the target to it
+        // To keep the index right, first this brand new vertex as the target
+        vertex_info.target_vertex_indices.insert(state.vertex_index);
+        state.node_to_vertex_index.insert({extra_node_id, state.vertex_index});
+        auto& extra_vertex_info = state.vertex_map[state.vertex_index++];
+        extra_vertex_info.node_id = extra_node_id;
+        extra_vertex_info.is_extra = true;
+        extra_vertex_info.original_node_id = source_node_id;
+        extra_vertex_info.target_vertex_indices.insert(it_target->second);
+    }
+    else
+    {
+        vertex_info.target_vertex_indices.insert(it_target->second);
+    }
+}
+
+
+template <operation_type TargetOperation, typename Turns, typename Clusters>
+void fill_vertex_map(Turns const& turns, Clusters const& clusters, state_type& state)
+{
+    std::set<std::size_t> visited_turns;
+    for (std::size_t i = 0; i < turns.size(); i++)
+    {
+        auto const & turn = turns[i];
+        if (turn.discarded)
+        {
+            continue;
+        }
+        if (visited_turns.count(i) > 0)
+        {
+            continue;
+        }
+
+        auto const source_node_id = get_node_id(turns, i);
+        auto const turn_indices = get_turn_indices_by_node_id(turns, clusters, source_node_id);
+
+        visited_turns.insert(turn_indices.begin(), turn_indices.end());
+
+        auto const target_nodes = get_target_nodes<TargetOperation>(turns, clusters, turn_indices);
+
+        for (auto const& target_node_id : target_nodes)
+        {
+            add_target_node(source_node_id, target_node_id, state, true);
+        }
+    }
+}
+
+// Assigns biconnected components to turns
+template <typename Turns, typename Clusters, typename Graph, typename Components>
+void assign_biconnected_component_ids(Turns& turns, Clusters const& clusters,
+    Graph const& graph, Components const& component, state_type const& state)
+{
+    auto node_id_from_it = [&state](auto const& it)
+    {
+        return it->second.is_extra
+            ? it->second.original_node_id
+            : it->second.node_id;
+    };    
+
+    typename graph_traits<Graph>::edge_iterator ei, ei_end;
+    for (boost::tie(ei, ei_end) = edges(graph); ei != ei_end; ++ei)
+    {
+        auto it_source = state.vertex_map.find(source(*ei, graph));
+        auto it_target = state.vertex_map.find(target(*ei, graph));
+        if (it_source == state.vertex_map.end() || it_target == state.vertex_map.end())
+        {
+            continue;
+        }
+
+        auto const source_node_id = node_id_from_it(it_source);
+        auto const target_node_id = node_id_from_it(it_target);
+
+        auto const source_turn_indices = get_turn_indices_by_node_id(turns, clusters, source_node_id);
+
+        // Assign the component to all the operations
+        // going from the source node to the target node.
+        for (auto const& turn_index : source_turn_indices)
+        {
+            auto& source_turn = turns[turn_index];
+            for (std::size_t j = 0; j < 2; j++)
+            {
+                auto& op = source_turn.operations[j];
+                if (op.enriched.travels_to_ip_index < 0)
+                {
+                    continue;
+                }
+                auto const travels_to_node_id = get_node_id(turns, op.enriched.travels_to_ip_index);
+                if (travels_to_node_id == target_node_id)
+                {
+                    op.enriched.component_id = static_cast<int>(component[*ei]);
+                }
+            }
+        }
+    }
+}
+
+template <operation_type TargetOperation, typename Turns, typename Clusters>
+void detect_biconnected_components(Turns& turns, Clusters const& clusters)
+{
+    using graph_t = boost::adjacency_list
+        <
+            boost::vecS,
+            boost::vecS,
+            boost::undirectedS,
+            boost::no_property,
+            boost::property<edge_component, std::size_t>
+        >;
+    using vertex_t = boost::graph_traits <graph_t>::vertex_descriptor;
+
+    // Mapping to add turns to vertices, count them, and then build the graph.
+    // (It is convenient if the vertex index is the same as the turn index.
+    // Therefore the default mapping is made like that, extra vertices
+    // are added later)
+
+    state_type state;
+    state.extra_node_id = static_cast<std::size_t>(turns.size());
+
+    fill_vertex_map<TargetOperation>(turns, clusters, state);
+
+    // Build the graph from the vertices
+    graph_t graph(state.vertex_map.size());
+    for (auto const& key_value : state.vertex_map)
+    {
+        auto const vertex_index = key_value.first;
+        for (auto const& target_vertex_index : key_value.second.target_vertex_indices)
+        {
+            add_edge(vertex_index, target_vertex_index, graph);
+        }
+    }
+
+    edge_component ec;
+    auto component = get(ec, graph);
+    biconnected_components(graph, component);
+    fix_components(component, graph);
+
+    assign_biconnected_component_ids(turns, clusters, graph, component, state);
+}
+
+
+}} // namespace detail::overlay
+#endif // DOXYGEN_NO_DETAIL
+
+}} // namespace boost::geometry
+
+#endif // BOOST_GEOMETRY_ALGORITHMS_DETAIL_OVERLAY_DETECT_ARTICULATION_POINTS_HPP

include/boost/geometry/algorithms/detail/overlay/enrichment_info.hpp

@@ -41,7 +41,6 @@ struct enrichment_info
         , rank(-1)
         , zone(-1)
         , region_id(-1)
-        , isolated(false)
     {}
 
     inline signed_size_type get_next_turn_index() const
@@ -69,7 +68,8 @@ struct enrichment_info
     signed_size_type rank; // in cluster
     signed_size_type zone; // open zone, in cluster
     signed_size_type region_id;
-    bool isolated;
+
+    signed_size_type component_id{-1};
 };
 
 

include/boost/geometry/algorithms/detail/overlay/graph_util.hpp

@@ -0,0 +1,67 @@
+// #define SKIP_SELF_TURNS
+
+// Boost.Geometry
+
+// Copyright (c) 2024 Barend Gehrels, Amsterdam, the Netherlands.
+
+// Use, modification and distribution is subject to the Boost Software License,
+// Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+
+#ifndef BOOST_GEOMETRY_ALGORITHMS_DETAIL_OVERLAY_GRAPH_UTIL_HPP
+#define BOOST_GEOMETRY_ALGORITHMS_DETAIL_OVERLAY_GRAPH_UTIL_HPP
+
+#include <boost/graph/biconnected_components.hpp>
+#include <boost/graph/adjacency_list.hpp>
+
+namespace boost { namespace geometry
+{
+
+#ifndef DOXYGEN_NO_DETAIL
+namespace detail { namespace overlay
+{
+
+struct edge_component
+{
+    using kind = edge_property_tag;
+};
+
+// It appears that in an undirected graph, the components for two edges are sometimes different. 
+// Fix that. To be found out why this is.
+template <typename Graph, typename Components>
+void fix_components(Components& components, Graph const& g)
+{
+    typename graph_traits<Graph>::edge_iterator ei, ei_end;
+    for (boost::tie(ei, ei_end) = edges(g); ei != ei_end; ++ei)
+    {
+        auto& component = components[*ei];
+
+        auto const source_vertex = source(*ei, g);
+        auto const target_vertex = target(*ei, g);
+
+        // Get the reverse edge and its component
+        auto const reverse_edge_pair = edge(target_vertex, source_vertex, g);
+        if (! reverse_edge_pair.second)
+        {
+            continue;
+        }
+
+        auto& reverse_component = components[reverse_edge_pair.first];
+
+        if (component != reverse_component)
+        {
+#if defined(BOOST_GEOMETRY_DEBUG_ARTICULATION_POINTS)
+            std::cout << "Fix component for edge <" << source_vertex << ", " << target_vertex << "> "
+                << component << " -> " << reverse_component << std::endl;
+#endif                
+            component = reverse_component;
+        }
+    }
+}
+
+}} // namespace detail::overlay
+#endif // DOXYGEN_NO_DETAIL
+
+}} // namespace boost::geometry
+
+#endif // BOOST_GEOMETRY_ALGORITHMS_DETAIL_OVERLAY_GRAPH_UTIL_HPP