CNetworkOfPoses.h

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/* +---------------------------------------------------------------------------+
   |                     Mobile Robot Programming Toolkit (MRPT)               |
   |                          http://www.mrpt.org/                             |
   |                                                                           |
   | Copyright (c) 2005-2017, Individual contributors, see AUTHORS file        |
   | See: http://www.mrpt.org/Authors - All rights reserved.                   |
   | Released under BSD License. See details in http://www.mrpt.org/License    |
   +---------------------------------------------------------------------------+ */
#ifndef CONSTRAINED_POSE_NETWORK_H
#define CONSTRAINED_POSE_NETWORK_H

/** \file The main class in this file is mrpt::poses::CNetworkOfPoses<>, a generic
           basic template for predefined 2D/3D graphs of pose contraints.
*/

#include <iostream>

#include <mrpt/graphs/CDirectedGraph.h>
#include <mrpt/graphs/CDirectedTree.h>
#include <mrpt/utils/CSerializable.h>
#include <mrpt/utils/CFileGZInputStream.h>
#include <mrpt/utils/CFileGZOutputStream.h>
#include <mrpt/utils/TParameters.h>
#include <mrpt/utils/traits_map.h>
#include <mrpt/utils/stl_serialization.h>
#include <mrpt/math/utils.h>
#include <mrpt/poses/poses_frwds.h>
#include <mrpt/system/os.h>
#include <mrpt/opengl/CSetOfObjects.h>
#include <mrpt/graphs/dijkstra.h>
#include <mrpt/graphs/TNodeAnnotations.h>
#include <mrpt/graphs/TMRSlamNodeAnnotations.h>
#include <mrpt/graphs/THypothesis.h>

#include <iterator>
#include <algorithm>
#if MRPT_HAS_CXX11
#include <type_traits>  // is_base_of()
#endif
#include <memory>

namespace mrpt
{
        namespace graphs
        {
                /** Internal functions for MRPT */
                namespace detail
                {
                        template <class GRAPH_T> struct graph_ops;

                        // forward declaration of CVisualizer
                        template<
                                class CPOSE, // Type of edges
                                class MAPS_IMPLEMENTATION,
                                class NODE_ANNOTATIONS,
                                class EDGE_ANNOTATIONS
                                >
                        class CVisualizer;
                        // forward declaration of CMRVisualizer
                        template<
                                class CPOSE, // Type of edges
                                class MAPS_IMPLEMENTATION,
                                class NODE_ANNOTATIONS,
                                class EDGE_ANNOTATIONS
                                >
                        class CMRVisualizer;

                }

                /** A directed graph of pose constraints, with edges being the relative poses between pairs of nodes identified by their numeric IDs (of type mrpt::utils::TNodeID).
                 *  A link or edge between two nodes "i" and "j", that is, the pose \f$ p_{ij} \f$, holds the relative position of "j" with respect to "i".
                 *   These poses are stored in the edges in the format specified by the template argument CPOSE. Users should employ the following derived classes
                 *   depending on the desired representation of edges:
                 *      - mrpt::graphs::CNetworkOfPoses2D    : 2D edges as a simple CPose2D (x y phi)
                 *      - mrpt::graphs::CNetworkOfPoses3D    : 3D edges as a simple mrpt::poses::CPose3D (x y z yaw pitch roll)
                 *      - mrpt::graphs::CNetworkOfPoses2DInf : 2D edges as a Gaussian PDF with information matrix (CPosePDFGaussianInf)
                 *      - mrpt::graphs::CNetworkOfPoses3DInf : 3D edges as a Gaussian PDF with information matrix (CPose3DPDFGaussianInf)
                 *      - mrpt::graphs::CNetworkOfPoses2DCov : 2D edges as a Gaussian PDF with covariance matrix (CPosePDFGaussian). It's more efficient to use the information matrix version instead!
                 *      - mrpt::graphs::CNetworkOfPoses3DCov : 3D edges as a Gaussian PDF with covariance matrix (CPose3DPDFGaussian). It's more efficient to use the information matrix version instead!
                 *
                 *  Two main members store all the information in this class:
                 *              - \a edges  (in the base class mrpt::graphs::CDirectedGraph::edges): A map from pairs of node ID -> pose constraints.
                 *              - \a nodes : A map from node ID -> estimated pose of that node (actually, read below on the template argument MAPS_IMPLEMENTATION).
                 *
                 *  Graphs can be loaded and saved to text file in the format used by TORO & HoG-man (more on the format <a href="http://www.mrpt.org/Robotics_file_formats" >here</a>),
                 *   using \a loadFromTextFile and \a saveToTextFile.
                 *
                 *  This class is the base for representing networks of poses, which are the main data type of a series
                 *   of SLAM algorithms implemented in the library mrpt-slam, in the namespace mrpt::graphslam.
                 *
                 *  The template arguments are:
                 *              - CPOSE: The type of the edges, which hold a relative pose (2D/3D, just a value or a Gaussian, etc.)
                 *              - MAPS_IMPLEMENTATION: Can be either mrpt::utils::map_traits_stdmap or mrpt::utils::map_traits_map_as_vector. Determines the type of the list of global poses (member \a nodes).
                 *
                 * \sa mrpt::graphslam
                 * \ingroup mrpt_graphs_grp
                 */
                template<
                        class CPOSE, // Type of edges
                        class MAPS_IMPLEMENTATION = mrpt::utils::map_traits_stdmap, // Use std::map<> vs. std::vector<>
                        class NODE_ANNOTATIONS = mrpt::graphs::detail::TNodeAnnotationsEmpty,
                        class EDGE_ANNOTATIONS = mrpt::graphs::detail::edge_annotations_empty
                        >
                class CNetworkOfPoses : public mrpt::graphs::CDirectedGraph< CPOSE, EDGE_ANNOTATIONS >
                {
                public:
                        /** @name Typedef's
                            @{ */
                        typedef mrpt::graphs::CDirectedGraph<CPOSE,EDGE_ANNOTATIONS> BASE;      //!< The base class "CDirectedGraph<CPOSE,EDGE_ANNOTATIONS>" */
                        typedef CNetworkOfPoses<CPOSE,MAPS_IMPLEMENTATION,NODE_ANNOTATIONS,EDGE_ANNOTATIONS> self_t; //!< My own type

                        typedef CPOSE              constraint_t;        //!< The type of PDF poses in the contraints (edges) (=CPOSE template argument)
                        typedef NODE_ANNOTATIONS   node_annotations_t;  //!< The extra annotations in nodes, apart from a \a constraint_no_pdf_t
                        typedef EDGE_ANNOTATIONS   edge_annotations_t;  //!< The extra annotations in edges, apart from a \a constraint_t

                        typedef MAPS_IMPLEMENTATION         maps_implementation_t; //!< The type of map's implementation (=MAPS_IMPLEMENTATION template argument)
                        typedef typename CPOSE::type_value  constraint_no_pdf_t;   //!< The type of edges or their means if they are PDFs (that is, a simple "edge" value)

                        /** The type of each global pose in \a nodes: an extension of the \a
                         * constraint_no_pdf_t pose with any optional user-defined data
                         */
                        struct global_pose_t : public constraint_no_pdf_t, public NODE_ANNOTATIONS
                        {
                                typedef typename CNetworkOfPoses<CPOSE,MAPS_IMPLEMENTATION,NODE_ANNOTATIONS,EDGE_ANNOTATIONS>::global_pose_t self_t;

                                /**\brief Potential class constructors
                                 */
                                /**\{ */
                                inline global_pose_t() : constraint_no_pdf_t() { }
                                template <typename ARG1> inline global_pose_t(const ARG1 &a1) : constraint_no_pdf_t(a1) { }
                                template <typename ARG1,typename ARG2> inline global_pose_t(const ARG1 &a1,const ARG2 &a2) : constraint_no_pdf_t(a1,a2) { }
                                /**\} */

                                /**\brief Copy constructor - delegate copying to the NODE_ANNOTATIONS
                                 * struct
                                 */
                                inline global_pose_t(const global_pose_t& other):
                                        constraint_no_pdf_t(other),
                                        NODE_ANNOTATIONS(other)
                                { }

                                inline bool operator==(const global_pose_t& other) const {
                                        return (
                                                        static_cast<const constraint_no_pdf_t>(*this) == static_cast<const constraint_no_pdf_t>(other) &&
                                                        static_cast<const NODE_ANNOTATIONS>(*this) == static_cast<const NODE_ANNOTATIONS>(other));
                                }
                                inline bool operator!=(const global_pose_t& other) const {
                                        return ( !(*this == other) );
                                }

                                inline friend std::ostream& operator<<(std::ostream& o, const self_t& global_pose) {
                                        o << global_pose.asString() << "| " <<  global_pose.retAnnotsAsString();
                                        return o;
                                }

                        };

                        /** A map from pose IDs to their global coordinate estimates, with uncertainty */
                        typedef typename MAPS_IMPLEMENTATION::template map<mrpt::utils::TNodeID,CPOSE> global_poses_pdf_t;

                        /** A map from pose IDs to their global coordinate estimates, without uncertainty (the "most-likely value") */
                        typedef typename MAPS_IMPLEMENTATION::template map<mrpt::utils::TNodeID,global_pose_t> global_poses_t;

                        /** @} */

                        /** @name Data members
                            @{ */

                        /** The nodes (vertices) of the graph, with their estimated "global"
                         * (with respect to \a root) position, without an associated covariance.
                         * \sa dijkstra_nodes_estimate
                         */
                        global_poses_t nodes;

                        /** The ID of the node that is the origin of coordinates, used as
                         * reference by all coordinates in \a nodes. By default, root is the ID
                         * "0". */
                        mrpt::utils::TNodeID root;

                        /** False (default) if an edge i->j stores the normal relative pose of j
                         * as seen from i: \f$ \Delta_i^j = j \ominus i \f$ True if an edge i->j
                         * stores the inverse relateive pose, that is, i as seen from j: \f$
                         * \Delta_i^j = i \ominus j \f$
                         */
                        bool edges_store_inverse_poses;

                        /** @} */


                        /** @name I/O file methods
                            @{ */

                        /** Saves to a text file in the format used by TORO & HoG-man (more on
                         * the format <a href="http://www.mrpt.org/Robotics_file_formats" * >here</a>)
                         * For 2D graphs only VERTEX2 & EDGE2 entries will be saved,
                         * and VERTEX3 & EDGE3 entries for 3D graphs.  Note that EQUIV entries
                         * will not be saved, but instead several EDGEs will be stored between
                         * the same node IDs.
                         *
                         * \sa saveToBinaryFile, loadFromTextFile
                         * \exception On any error
                         */
                        inline void saveToTextFile(const std::string &fileName) const {
                                detail::graph_ops<self_t>::save_graph_of_poses_to_text_file(this,fileName);
                        }

                        /** Loads from a text file in the format used by TORO & HoG-man (more on the format <a href="http://www.mrpt.org/Robotics_file_formats" >here</a>)
                         *   Recognized line entries are: VERTEX2, VERTEX3, EDGE2, EDGE3, EQUIV.
                         *   If an unknown entry is found, a warning is dumped to std::cerr (only once for each unknown keyword).
                         *   An exception will be raised if trying to load a 3D graph into a 2D class (in the opposite case, missing 3D data will default to zero).
                         *
                         * \param[in] fileName The file to load.
                         * \param[in] collapse_dup_edges If true, \a collapseDuplicatedEdges will be
                         * called automatically after loading (note that this operation may take
                         * significant time for very large graphs).
                         *
                         * \sa loadFromBinaryFile, saveToTextFile
                         *
                         * \exception On any error, as a malformed line or loading a 3D graph in
                         * a 2D graph.
                         */
                        inline void loadFromTextFile(const std::string &fileName, bool collapse_dup_edges = true) {
                                detail::graph_ops<self_t>::load_graph_of_poses_from_text_file(this,fileName);
                                if (collapse_dup_edges) this->collapseDuplicatedEdges();
                        }

                        /** @} */

                        /** @name Utility methods
                            @{ */
                        /**\brief Return 3D Visual Representation of the edges and nodes in the
                         * network of poses
                         *
                         * Method makes the call to the corresponding method of the CVisualizer
                         * class instance.
                         */
                        void getAs3DObject(
                                        mrpt::opengl::CSetOfObjectsPtr object,
                                        const mrpt::utils::TParametersDouble& viz_params) const
                        {
                                typedef mrpt::graphs::detail::CVisualizer<CPOSE, MAPS_IMPLEMENTATION, NODE_ANNOTATIONS, EDGE_ANNOTATIONS> visualizer_t;
                                typedef mrpt::graphs::detail::CMRVisualizer<CPOSE, MAPS_IMPLEMENTATION, NODE_ANNOTATIONS, EDGE_ANNOTATIONS> visualizer_multirobot_t;

                                bool is_multirobot=false;
#if MRPT_HAS_CXX11
                                std::unique_ptr<visualizer_t> viz;
                                is_multirobot = (std::is_base_of<mrpt::graphs::detail::TMRSlamNodeAnnotations,global_pose_t>::value);
#else
                                std::auto_ptr<visualizer_t> viz;
                                // Initialize instance of class visualizer
                                global_pose_t n;
                                is_multirobot = dynamic_cast<mrpt::graphs::detail::TMRSlamNodeAnnotations*>(&n)!=NULL;
#endif
                                if (is_multirobot) {
                                        viz.reset(new visualizer_multirobot_t(*this));
                                }
                                else {
                                        viz.reset(new visualizer_t(*this));
                                }
                                viz->getAs3DObject(object, viz_params);
                        }

                        /** Spanning tree computation of a simple estimation of the global
                         * coordinates of each node just from the information in all edges,
                         * sorted in a Dijkstra tree based on the current "root" node.
                         *
                         * \note The "global" coordinates are with respect to the node with the
                         * ID specified in \a root.
                         *
                         * \note This method takes into account the
                         * value of \a edges_store_inverse_poses
                         *
                         * \sa node, root
                         */
                        inline void dijkstra_nodes_estimate() { detail::graph_ops<self_t>::graph_of_poses_dijkstra_init(this); }

                        /** Look for duplicated edges (even in opposite directions) between all
                         * pairs of nodes and fuse them.  Upon return, only one edge remains
                         * between each pair of nodes with the mean & covariance (or information
                         * matrix) corresponding to the Bayesian fusion of all the Gaussians.
                         *
                         * \return Overall number of removed edges.
                         */
                        inline size_t collapseDuplicatedEdges() { return detail::graph_ops<self_t>::graph_of_poses_collapse_dup_edges(this); }

                        /** Computes the overall square error from all the pose constraints (edges) with respect to the global poses in \a nodes
                         *  If \a ignoreCovariances is false, the squared Mahalanobis distance will be computed instead of the straight square error.
                         * \sa getEdgeSquareError
                         * \exception std::exception On global poses not in \a nodes
                         */
                        double getGlobalSquareError(bool ignoreCovariances = true) const {
                                double sqErr=0;
                                const typename BASE::edges_map_t::const_iterator last_it=BASE::edges.end();
                                for (typename BASE::edges_map_t::const_iterator itEdge=BASE::edges.begin();itEdge!=last_it;++itEdge)
                                        sqErr+=detail::graph_ops<self_t>::graph_edge_sqerror(this,itEdge,ignoreCovariances);
                                return sqErr;
                        }

                        /**\brief Find the edges between the nodes in the node_IDs set and fill
                         * given graph pointer accordingly.
                         *
                         * \param[in] node_IDs Set of nodes, between which, edges should be found
                         * and inserted in the given sub_graph pointer
                         * \param[in] root_node_in Node ID to be used as the root node of
                         * sub_graph. If this is not given, the lowest nodeID is to be used.
                         * \param[out] CNetworkOfPoses pointer that is to be filled.
                         *
                         * \param[in] auto_expand_set If true and in case the node_IDs set
                         * contains non-consecutive nodes the returned set is expanded with the
                         * in-between nodes. This makes sure that the final graph is always
                         * connected.
                         * If auto_expand_set is false  but there exist
                         * non-consecutive nodes, virtual edges are inserted in the parts that
                         * the graph is not connected
                         */
                        void extractSubGraph(const std::set<TNodeID>& node_IDs,
                                        self_t* sub_graph,
                                        const TNodeID root_node_in=INVALID_NODEID,
                                        const bool& auto_expand_set=true) const {
                                using namespace std;
                                using namespace mrpt;
                                using namespace mrpt::math;
                                using namespace mrpt::graphs::detail;

                                typedef CDijkstra<self_t, MAPS_IMPLEMENTATION> dijkstra_t;

                                // assert that the given pointers are valid
                                ASSERTMSG_(sub_graph,
                                                "\nInvalid pointer to a CNetworkOfPoses instance is given. Exiting..\n");
                                sub_graph->clear();

                                // assert that the root_node actually exists in the given node_IDs set
                                TNodeID root_node = root_node_in;
                                if (root_node != INVALID_NODEID) {
                                        ASSERTMSG_(node_IDs.find(root_node) != node_IDs.end(),
                                                        "\nRoot_node does not exist in the given node_IDs set. Exiting.\n");
                                }

                                // ask for at least 2 nodes
                                ASSERTMSG_(node_IDs.size() >= 2,
                                                format(
                                                        "Very few nodes [%lu] for which to extract a subgraph. Exiting\n",
                                                        static_cast<unsigned long>(node_IDs.size())));


                                // find out if querry contains non-consecutive nodes.
                                // Assumption: Set elements are in standard, ascending order.
                                bool is_fully_connected_graph = true;
                                std::set<TNodeID> node_IDs_real; // actual set of nodes to be used.
                                if (*node_IDs.rbegin() - *node_IDs.begin() + 1 == node_IDs.size()) {
                                        node_IDs_real = node_IDs;
                                }
                                else { // contains non-consecutive nodes
                                        is_fully_connected_graph = false;

                                        if (auto_expand_set) { // set auto-expansion
                                                for (TNodeID curr_node_ID = *node_IDs.begin();
                                                                curr_node_ID != *node_IDs.rbegin(); ++curr_node_ID) {
                                                        node_IDs_real.insert(curr_node_ID);
                                                }
                                        }
                                        else { // virtual_edge_addition strategy
                                                node_IDs_real = node_IDs;
                                        }
                                }

                                // add all the nodes of the node_IDs_real set to sub_graph
                                for (std::set<TNodeID>::const_iterator
                                                node_IDs_it = node_IDs_real.begin();
                                                node_IDs_it != node_IDs_real.end();
                                                ++node_IDs_it) {

                                        // assert that current node exists in *own* graph
                                        typename global_poses_t::const_iterator own_it;
                                        for (own_it = nodes.begin(); own_it != nodes.end(); ++own_it) {
                                                if (*node_IDs_it == own_it->first) {
                                                        break; // I throw exception afterwards
                                                }
                                        }
                                        ASSERTMSG_(own_it != nodes.end(),
                                                        format("NodeID [%lu] can't be found in the initial graph.",
                                                                static_cast<unsigned long>(*node_IDs_it)));

                                        global_pose_t curr_node(nodes.at(*node_IDs_it));
                                        sub_graph->nodes.insert(make_pair(*node_IDs_it, curr_node));

                                }
                                //cout << "Extracting subgraph for nodeIDs: " <<
                                        //getSTLContainerAsString(node_IDs_real) << endl;

                                // set the root of the extracted graph
                                if (root_node == INVALID_NODEID) {
                                        // smallest nodeID by default
                                        // http://stackoverflow.com/questions/1342045/how-do-i-find-the-largest-int-in-a-stdsetint
                                        // std::set sorts elements in ascending order
                                        root_node = sub_graph->nodes.begin()->first;
                                }
                                sub_graph->root = root_node;

                                // TODO - Remove these lines - not needed
                                // set the corresponding root pose
                                //sub_graph->nodes.at(sub_graph->root) = nodes.at(sub_graph->root);

                                // find all edges (in the initial graph), that exist in the given set
                                // of nodes; add them to the given graph
                                sub_graph->clearEdges();
                                for (typename BASE::const_iterator it = BASE::edges.begin();
                                                it != BASE::edges.end();
                                                ++it) {

                                        const TNodeID& from = it->first.first;
                                        const TNodeID& to = it->first.second;
                                        const typename BASE::edge_t& curr_edge = it->second;

                                        // if both nodes exist in the given set, add the corresponding edge
                                        if (sub_graph->nodes.find(from) != sub_graph->nodes.end() &&
                                                        sub_graph->nodes.find(to) != sub_graph->nodes.end()) {
                                                sub_graph->insertEdge(from, to, curr_edge);
                                        }
                                }

                                if (!auto_expand_set && !is_fully_connected_graph) {
                                        // Addition of virtual edges between non-connected graph parts is necessary

                                        // make sure that the root nodeID is connected to at least one node
                                        {
                                                std::set<TNodeID> root_neighbors;
                                                sub_graph->getNeighborsOf(sub_graph->root, root_neighbors);

                                                if (root_neighbors.empty()) {
                                                        // add an edge between the root and an adjacent nodeID
                                                        typename global_poses_t::iterator root_it =
                                                                sub_graph->nodes.find(sub_graph->root);
                                                        ASSERT_(root_it != sub_graph->nodes.end());
                                                        if ((*root_it == *sub_graph->nodes.rbegin())) { // is the last nodeID
                                                                // add with previous node
                                                                TNodeID next_to_root = (--root_it)->first;
                                                                self_t::addVirtualEdge(sub_graph, next_to_root, sub_graph->root);
                                                                //cout << "next_to_root = " << next_to_root;
                                                        }
                                                        else {
                                                                TNodeID next_to_root = (++root_it)->first;
                                                                //cout << "next_to_root = " << next_to_root;
                                                                self_t::addVirtualEdge(sub_graph, sub_graph->root, next_to_root);
                                                        }

                                                }
                                        }


                                        // as long as the graph is unconnected (as indicated by Dijkstra) add a virtual edge between
                                        bool dijkstra_runs_successfully = false;

                                        // loop until the graph is fully connected (i.e. I can reach every
                                        // node of the graph starting from its root)
                                        while (!dijkstra_runs_successfully) {
                                                try {
                                                        dijkstra_t dijkstra(*sub_graph, sub_graph->root);
                                                        dijkstra_runs_successfully = true;
                                                }
                                                catch (const mrpt::graphs::detail::NotConnectedGraph& ex) {
                                                        dijkstra_runs_successfully = false;

                                                        set<TNodeID> unconnected_nodeIDs;
                                                        ex.getUnconnectedNodeIDs(&unconnected_nodeIDs);
                                                        //cout << "Unconnected nodeIDs: " << mrpt::math::getSTLContainerAsString(unconnected_nodeIDs) << endl;
                                                        // mainland: set of nodes that the root nodeID is in
                                                        // island: set of nodes that the Dijkstra graph traversal can't
                                                        // reach starting from the root.
                                                        // [!] There may be multiple sets of these nodes

                                                        // set::rend() is the element with the highest value
                                                        // set::begin() is the element with the lowest value
                                                        const TNodeID& island_highest = *unconnected_nodeIDs.rbegin();
                                                        const TNodeID& island_lowest = *unconnected_nodeIDs.begin();
                                                        //cout << "island_highest: " << island_highest << endl;
                                                        //cout << "island_lowest: " << island_lowest << endl;
                                                        //cout << "root: " << sub_graph->root << endl;

                                                        // find out which nodes are in the same partition with the root
                                                        // (i.e. mainland)
                                                        std::set<TNodeID> mainland;
                                                        // for all nodes in sub_graph
                                                        for (typename global_poses_t::const_iterator
                                                                        n_it = sub_graph->nodes.begin();
                                                                        n_it != sub_graph->nodes.end();
                                                                        ++n_it) {
                                                                bool is_there = false;

                                                                // for all unconnected nodes
                                                                for (typename std::set<TNodeID>::const_iterator
                                                                                uncon_it = unconnected_nodeIDs.begin();
                                                                                uncon_it != unconnected_nodeIDs.end();
                                                                                ++uncon_it) {

                                                                        if (n_it->first == *uncon_it) {
                                                                                is_there = true;
                                                                                break;
                                                                        }
                                                                }

                                                                if (!is_there) {
                                                                        mainland.insert(n_it->first);
                                                                }
                                                        }

                                                        bool is_single_island = (island_highest - island_lowest + 1 ==
                                                                        unconnected_nodeIDs.size());

                                                        if (is_single_island) { // single island
                                                                // Possible scenarios:
                                                                // | island                       |                            | mainland                                   |
                                                                // | <low nodeIDs>  island_highest|  --- <virtual_edge> --->>  | mainland_lowest <high nodeIDs> ... root ...|
                                                                // --- OR ---
                                                                // | mainland                       |                            | island                       |
                                                                // | <low nodeIDs>  mainland_highest|  --- <virtual_edge> --->>  | island_lowest <high nodeIDs> |

                                                                const std::set<TNodeID>& island = unconnected_nodeIDs;
                                                                this->connectGraphPartitions(sub_graph, island, mainland);

                                                        }
                                                        else { // multiple islands
                                                                // add a virtual edge between the last group before the mainland and the mainland

                                                                // split the unconnected_nodeIDs to smaller groups of  nodes
                                                                // we only care about the nodes that are prior to the root
                                                                std::vector<std::set<TNodeID> > vec_of_islands;
                                                                std::set<TNodeID> curr_island;
                                                                TNodeID prev_nodeID = *unconnected_nodeIDs.begin();
                                                                curr_island.insert(prev_nodeID); // add the initial node;
                                                                for (std::set<TNodeID>::const_iterator
                                                                                it = ++unconnected_nodeIDs.begin();
                                                                                *it < sub_graph->root && it != unconnected_nodeIDs.end();
                                                                                ++it) {
                                                                        if (!(absDiff(*it, prev_nodeID) == 1)) {
                                                                                vec_of_islands.push_back(curr_island);
                                                                                curr_island.clear();
                                                                        }
                                                                        curr_island.insert(*it);

                                                                        // update the previous nodeID
                                                                        prev_nodeID = *it;
                                                                }
                                                                vec_of_islands.push_back(curr_island);

                                                                //cout << "last_island: " << getSTLContainerAsString(vec_of_islands.back()) << endl;
                                                                //cout << "mainland: " << getSTLContainerAsString(mainland) << endl;
                                                                this->connectGraphPartitions(sub_graph, vec_of_islands.back(), mainland);
                                                        }
                                                }
                                        }
                                }

                                // estimate the node positions according to the edges - root is (0, 0, 0)
                                // just execute dijkstra once for grabbing the updated node positions.
                                sub_graph->dijkstra_nodes_estimate();

                        } // end of extractSubGraph

                        /**\brief Integrate given graph into own graph using the list of provided
                         * common THypotheses. Nodes of the other graph are renumbered upon
                         * integration in own graph.
                         *
                         * \param[in] other Graph (of the same type) that is to be integrated with own graph.
                         * \param[in] Hypotheses that join own and other graph.
                         * \param[in] hypots_from_other_to_self Specify the direction of the
                         * THypothesis objects in the common_hypots. If true (default) they are
                         * directed from other to own graph (other \rightarrow own),
                         *
                         * \param[out] old_to_new_nodeID_mappings_out Map from the old nodeIDs
                         * that are in the given graph to the new nodeIDs that have been inserted
                         * (by this method) in own graph.
                         */
                        inline void mergeGraph(
                                        const self_t& other,
                                        const typename std::vector<detail::THypothesis<self_t> >& common_hypots,
                                        const bool hypots_from_other_to_self=true,
                                        std::map<TNodeID, TNodeID>* old_to_new_nodeID_mappings_out=NULL) {
                                MRPT_START;
                                using namespace mrpt::graphs;
                                using namespace mrpt::utils;
                                using namespace mrpt::graphs::detail;
                                using namespace std;

                                typedef typename vector<THypothesis<self_t> >::const_iterator hypots_cit_t;
                                typedef typename global_poses_t::const_iterator nodes_cit_t;

                                const self_t& graph_from = (hypots_from_other_to_self? other : *this);
                                const self_t& graph_to = (hypots_from_other_to_self? *this : other);

                                // assert that both own and other graph have at least two nodes.
                                ASSERT_(graph_from.nodes.size() >= 2);
                                ASSERT_(graph_to.nodes.size() >= 2);

                                // Assert that from-nodeIds, to-nodeIDs in common_hypots exist in own
                                // and other graph respectively
                                for (hypots_cit_t h_cit = common_hypots.begin();
                                                h_cit != common_hypots.end();
                                                ++h_cit) {

                                        ASSERTMSG_(graph_from.nodes.find(h_cit->from) != graph_from.nodes.end(),
                                                        format("NodeID %lu is not found in (from) graph", h_cit->from))
                                        ASSERTMSG_(graph_to.nodes.find(h_cit->to) != graph_to.nodes.end(),
                                                        format("NodeID %lu is not found in (to) graph", h_cit->to))
                                }

                                // find the max nodeID in existing graph
                                TNodeID max_nodeID = 0;
                                for (nodes_cit_t n_cit = this->nodes.begin();
                                                n_cit != this->nodes.end();
                                                ++n_cit) {
                                        if (n_cit->first > max_nodeID) {
                                                max_nodeID = n_cit->first;
                                        }
                                }
                                TNodeID renum_start = max_nodeID + 1;
                                size_t renum_counter = 0;
                                //cout << "renum_start: " << renum_start << endl;

                                // Renumber nodeIDs of other graph so that they don't overlap with own
                                // graph nodeIDs
                                std::map<TNodeID, TNodeID>* old_to_new_nodeID_mappings;

                                // map of TNodeID->TNodeID correspondences to address to if the
                                // old_to_new_nodeID_mappings_out is not given.
                                // Handy for not having to allocate old_to_new_nodeID_mappings in the
                                // heap
                                std::map<TNodeID, TNodeID> mappings_tmp;

                                // If given, use the old_to_new_nodeID_mappings map.
                                if (old_to_new_nodeID_mappings_out) {
                                        old_to_new_nodeID_mappings = old_to_new_nodeID_mappings_out;
                                }
                                else {
                                        old_to_new_nodeID_mappings = &mappings_tmp;
                                }
                                old_to_new_nodeID_mappings->clear();

                                // add all nodes of other graph - Take care of renumbering them
                                //cout << "Adding nodes of other graph" << endl;
                                //cout << "====================" << endl;
                                for (nodes_cit_t n_cit = other.nodes.begin();
                                                n_cit != other.nodes.end();
                                                ++n_cit) {
                                        TNodeID new_nodeID = renum_start + renum_counter++;
                                        old_to_new_nodeID_mappings->insert(make_pair(
                                                                n_cit->first,
                                                                new_nodeID));
                                        this->nodes.insert(make_pair(
                                                                new_nodeID, n_cit->second));

                                        //cout << "Adding nodeID: " << new_nodeID << endl;
                                }

                                // add common constraints
                                //cout << "Adding common constraints" << endl;
                                //cout << "====================" << endl;
                                for (hypots_cit_t h_cit = common_hypots.begin();
                                                h_cit != common_hypots.end();
                                                ++h_cit) {
                                        TNodeID from, to;
                                        if (hypots_from_other_to_self) {
                                                from = old_to_new_nodeID_mappings->at(h_cit->from);
                                                to = h_cit->to;
                                        }
                                        else {
                                                from = h_cit->from;
                                                to = old_to_new_nodeID_mappings->at(h_cit->to);
                                        }
                                        this->insertEdge(from, to, h_cit->getEdge());
                                        //cout << from << " -> " << to << " => " << h_cit->getEdge() << endl;
                                }

                                // add all constraints of the other graph
                                //cout << "Adding constraints of other graph" << endl;
                                //cout << "====================" << endl;
                                for (typename self_t::const_iterator
                                                g_cit = other.begin();
                                                g_cit != other.end();
                                                ++g_cit) {
                                        TNodeID new_from = old_to_new_nodeID_mappings->at(g_cit->first.first);
                                        TNodeID new_to = old_to_new_nodeID_mappings->at(g_cit->first.second);
                                        this->insertEdge(new_from, new_to, g_cit->second);

                                        //cout << "[" << new_from << "] -> [" << new_to << "]" << " => " << g_cit->second << endl;
                                }

                                // run Dijkstra to update the node positions
                                this->dijkstra_nodes_estimate();

                                MRPT_END;
                        }

                        /**\brief Add an edge between the last node of the group with the lower
                         * nodeIDs and the first node of the higher nodeIDs.
                         *
                         * Given groups of nodes should only contain consecutive nodeIDs and
                         * there should be no overlapping between them
                         *
                         * \note It is assumed that the sets of nodes are \b already in ascending
                         * order (default std::set behavior.
                         */
                        inline static void connectGraphPartitions(
                                        self_t* sub_graph,
                                        const std::set<TNodeID>& groupA,
                                        const std::set<TNodeID>& groupB) {
                                using namespace mrpt::math;

                                ASSERTMSG_(sub_graph,
                                                "\nInvalid pointer to a CNetworkOfPoses instance is given. Exiting..\n");
                                ASSERTMSG_(!groupA.empty(), "\ngroupA is empty.");
                                ASSERTMSG_(!groupB.empty(), "\ngroupB is empty.");

                                // assertion - non-overlapping groups
                                ASSERTMSG_(
                                                *groupA.rend() < *groupB.rbegin() ||
                                                *groupA.rbegin() > *groupB.rend(),
                                                "Groups A, B contain overlapping nodeIDs");

                                // decide what group contains the low/high nodeIDs
                                // just compare any two nodes of the sets (they are non-overlapping
                                const std::set<TNodeID>& low_nodeIDs =
                                                *groupA.rbegin() < *groupB.rbegin() ?  groupA : groupB;
                                const std::set<TNodeID>& high_nodeIDs =
                                                *groupA.rbegin() > *groupB.rbegin() ? groupA : groupB;

                                // add virtual edge
                                const TNodeID& from_nodeID = *low_nodeIDs.rbegin();
                                const TNodeID& to_nodeID = *high_nodeIDs.begin();
                                self_t::addVirtualEdge(sub_graph, from_nodeID, to_nodeID);

                        }

                        /** Computes the square error of one pose constraints (edge) with respect
                         * to the global poses in \a nodes If \a ignoreCovariances is false, the
                         * squared Mahalanobis distance will be computed instead of the straight
                         * square error.
                         *
                         * \exception std::exception On global poses not in \a nodes
                         */
                        inline double getEdgeSquareError(
                                        const typename BASE::edges_map_t::const_iterator &itEdge,
                                        bool ignoreCovariances = true) const {

                                return detail::graph_ops<self_t>::graph_edge_sqerror(
                                                this,
                                                itEdge,
                                                ignoreCovariances);
                        }

                        /** Computes the square error of one pose constraints (edge) with respect
                         * to the global poses in \a nodes If \a ignoreCovariances is false, the
                         * squared Mahalanobis distance will be computed instead of the straight
                         * square error.
                         *
                         * \exception std::exception On edge not existing or global poses not in
                         * \a nodes
                         */
                        double getEdgeSquareError(const mrpt::utils::TNodeID from_id, const mrpt::utils::TNodeID to_id, bool ignoreCovariances = true) const
                        {
                                const typename BASE::edges_map_t::const_iterator itEdge = BASE::edges.find(std::make_pair(from_id,to_id));
                                ASSERTMSG_(itEdge!=BASE::edges.end(),format("Request for edge %u->%u that doesn't exist in graph.",static_cast<unsigned int>(from_id),static_cast<unsigned int>(to_id)));
                                return getEdgeSquareError(itEdge,ignoreCovariances);
                        }

                        /** Empty all edges, nodes and set root to ID 0. */
                        inline void clear() {
                                BASE::edges.clear();
                                nodes.clear();
                                root = 0;
                                edges_store_inverse_poses = false;
                        }

                        /** Return number of nodes in the list \a nodes of global coordinates
                         * (may be different that all nodes appearing in edges)
                         *
                         * \sa mrpt::graphs::CDirectedGraph::countDifferentNodesInEdges
                         */
                        inline size_t nodeCount() const { return nodes.size(); }

                        /**  @} */

                        /** @name Ctors & Dtors
                          @{ */

                        /** Default constructor (just sets root to "0" and
                         * edges_store_inverse_poses to "false") */
                        inline CNetworkOfPoses():
                                root(0),
                                edges_store_inverse_poses(false)
                        {
                        }
                        /** @} */

                private:
                        /**\brief Add a virtual edge between two nodes in the given graph.
                         *
                         * Edge is called virtual as its value will be determined solely on the
                         * pose difference of the given nodeIDs
                         */
                        inline static void addVirtualEdge(
                                        self_t* graph,
                                        const TNodeID& from,
                                        const TNodeID& to) {
                                ASSERTMSG_(graph, "Invalid pointer to the graph instance was provided.");

                                typename self_t::global_pose_t& p_from = graph->nodes.at(from);
                                typename self_t::global_pose_t& p_to = graph->nodes.at(to);
                                const typename BASE::edge_t& virt_edge(p_to - p_from);

                                graph->insertEdge(from, to, virt_edge);
                        }

                };  // end class

                /** Binary serialization (write) operator "stream << graph" */
                template <class CPOSE,class MAPS_IMPLEMENTATION,class NODE_ANNOTATIONS,class EDGE_ANNOTATIONS>
                        mrpt::utils::CStream & operator << (mrpt::utils::CStream&out, const CNetworkOfPoses<CPOSE,MAPS_IMPLEMENTATION,NODE_ANNOTATIONS,EDGE_ANNOTATIONS> &obj)
                        {
                                typedef CNetworkOfPoses<CPOSE,MAPS_IMPLEMENTATION,NODE_ANNOTATIONS,EDGE_ANNOTATIONS> graph_t;
                                detail::graph_ops<graph_t>::save_graph_of_poses_to_binary_file(&obj,out);
                                return out;
                        }

                /** Binary serialization (read) operator "stream >> graph" */
                template <class CPOSE,class MAPS_IMPLEMENTATION,class NODE_ANNOTATIONS,class EDGE_ANNOTATIONS>
                        mrpt::utils::CStream & operator >> (mrpt::utils::CStream&in, CNetworkOfPoses<CPOSE,MAPS_IMPLEMENTATION,NODE_ANNOTATIONS,EDGE_ANNOTATIONS> &obj)
                        {
                                typedef CNetworkOfPoses<CPOSE,MAPS_IMPLEMENTATION,NODE_ANNOTATIONS,EDGE_ANNOTATIONS> graph_t;
                                detail::graph_ops<graph_t>::read_graph_of_poses_from_binary_file(&obj,in);
                                return in;
                        }

                /** \addtogroup mrpt_graphs_grp
                 * \name Handy typedefs for CNetworkOfPoses commonly used types
                 @{ */

                typedef CNetworkOfPoses<mrpt::poses::CPose2D,mrpt::utils::map_traits_stdmap> CNetworkOfPoses2D;     //!< The specialization of CNetworkOfPoses for poses of type CPose2D (not a PDF!), also implementing serialization.
                typedef CNetworkOfPoses<mrpt::poses::CPose3D,mrpt::utils::map_traits_stdmap> CNetworkOfPoses3D;     //!< The specialization of CNetworkOfPoses for poses of type mrpt::poses::CPose3D (not a PDF!), also implementing serialization.
                typedef CNetworkOfPoses<mrpt::poses::CPosePDFGaussian, mrpt::utils::map_traits_stdmap> CNetworkOfPoses2DCov;  //!< The specialization of CNetworkOfPoses for poses of type CPosePDFGaussian, also implementing serialization.
                typedef CNetworkOfPoses<mrpt::poses::CPose3DPDFGaussian, mrpt::utils::map_traits_stdmap> CNetworkOfPoses3DCov;  //!< The specialization of CNetworkOfPoses for poses of type CPose3DPDFGaussian, also implementing serialization.
                typedef CNetworkOfPoses<mrpt::poses::CPosePDFGaussianInf, mrpt::utils::map_traits_stdmap> CNetworkOfPoses2DInf;  //!< The specialization of CNetworkOfPoses for poses of type CPosePDFGaussianInf, also implementing serialization.
                typedef CNetworkOfPoses<mrpt::poses::CPose3DPDFGaussianInf, mrpt::utils::map_traits_stdmap> CNetworkOfPoses3DInf;  //!< The specialization of CNetworkOfPoses for poses of type CPose3DPDFGaussianInf, also implementing serialization.

                /**\brief Specializations of CNetworkOfPoses for graphs whose nodes inherit from TMRSlamNodeAnnotations struct */
                /**\{ */
                typedef CNetworkOfPoses<mrpt::poses::CPosePDFGaussianInf, mrpt::utils::map_traits_stdmap, mrpt::graphs::detail::TMRSlamNodeAnnotations> CNetworkOfPoses2DInf_NA;
                typedef CNetworkOfPoses<mrpt::poses::CPose3DPDFGaussianInf, mrpt::utils::map_traits_stdmap, mrpt::graphs::detail::TMRSlamNodeAnnotations> CNetworkOfPoses3DInf_NA;
                /**\} */

                /** @} */  // end of grouping


        } // End of namespace

        // Specialization of TTypeName must occur in the same namespace:
        namespace utils
        {
                // Extensions to mrpt::utils::TTypeName for matrices:
                template<
                        class CPOSE,
                        class MAPS_IMPLEMENTATION,
                        class NODE_ANNOTATIONS,
                        class EDGE_ANNOTATIONS
                        >
                struct TTypeName <mrpt::graphs::CNetworkOfPoses<CPOSE,MAPS_IMPLEMENTATION,NODE_ANNOTATIONS,EDGE_ANNOTATIONS> >
                {
                        static std::string get()
                        {
                                return std::string("mrpt::graphs::CNetworkOfPoses<")
                                        +TTypeName<CPOSE>::get() + std::string(",")
                                        +TTypeName<MAPS_IMPLEMENTATION>::get() + std::string(",")
                                        +TTypeName<NODE_ANNOTATIONS>::get() + std::string(",")
                                        +TTypeName<EDGE_ANNOTATIONS>::get()
                                        +std::string(">");
                        }
                };

                MRPT_DECLARE_TTYPENAME(mrpt::utils::map_traits_stdmap)
                MRPT_DECLARE_TTYPENAME(mrpt::utils::map_traits_map_as_vector)

        }

} // End of namespace


// Implementation of templates (in a separate file for clarity)
#include "CNetworkOfPoses_impl.h"

// Visualization related template classes
#include <mrpt/graphs/CVisualizer.h>
#include <mrpt/graphs/CMRVisualizer.h>

#endif