Class LazyPRM

Nested Relationships

Nested Types

Inheritance Relationships

Base Type

Derived Type

Class Documentation

class LazyPRM : public ompl::base::Planner

Lazy Probabilistic RoadMap planner.

Short description

LazyPRM is a planner that constructs a roadmap of milestones that approximate the connectivity of the state space, just like PRM does. The difference is that the planner uses lazy collision checking.

External documentation

R. Bohlin and L.E. Kavraki Path Planning Using Lazy PRM IEEE International Conference on Robotics and Automation, San Francisco, pp. 521–528, 2000. DOI: 10.1109/ROBOT.2000.844107[more]

Subclassed by ompl::geometric::LazyPRMstar

Public Types

using Vertex = boost::adjacency_list_traits<boost::vecS, boost::listS, boost::undirectedS>::vertex_descriptor

The type for a vertex in the roadmap.

using Graph = boost::adjacency_list<boost::vecS, boost::listS, boost::undirectedS, boost::property<vertex_state_t, base::State*, boost::property<boost::vertex_index_t, unsigned long int, boost::property<vertex_flags_t, unsigned int, boost::property<vertex_component_t, unsigned long int, boost::property<boost::vertex_predecessor_t, Vertex, boost::property<boost::vertex_rank_t, unsigned long int>>>>>>, boost::property<boost::edge_weight_t, base::Cost, boost::property<edge_flags_t, unsigned int>>>

The underlying roadmap graph.

Any BGL graph representation could be used here. Because we

expect the roadmap to be sparse (m<n^2), an adjacency_list is more appropriate than an adjacency_matrix. We use listS for the vertex list because vertex descriptors are invalidated by remove operations if using vecS.

Obviously, a ompl::base::State* vertex property is required.

The incremental connected components algorithm requires vertex_predecessor_t and vertex_rank_t properties. If boost::vecS is not used for vertex storage, then there must also be a boost:vertex_index_t property manually added.

Edges should be undirected and have a weight property.

using Edge = boost::graph_traits<Graph>::edge_descriptor

The type for an edge in the roadmap.

using RoadmapNeighbors = std::shared_ptr<NearestNeighbors<Vertex>>

A nearest neighbors data structure for roadmap vertices.

using ConnectionStrategy = std::function<const std::vector<Vertex>&(const Vertex)>

A function returning the milestones that should be attempted to connect to.

using ConnectionFilter = std::function<bool(const Vertex&, const Vertex&)>

A function that can reject connections.

This is called after previous connections from the neighbor list have been added to the roadmap.

Public Functions

LazyPRM(const base::SpaceInformationPtr &si, bool starStrategy = false)

Constructor.

LazyPRM(const base::PlannerData &data, bool starStrategy = false)

Constructor.

~LazyPRM() override
void setRange(double distance)

Set the maximum length of a motion to be added to the roadmap.

inline double getRange() const

Get the range the planner is using.

template<template<typename T> class NN>
inline void setNearestNeighbors()

Set a different nearest neighbors datastructure.

void setProblemDefinition(const base::ProblemDefinitionPtr &pdef) override
inline void setConnectionStrategy(const ConnectionStrategy &connectionStrategy)

Set the connection strategy function that specifies the milestones that connection attempts will be make to for a given milestone.

The behavior and performance of PRM can be changed drastically

by varying the number and properties if the milestones that are connected to each other.

Parameters:

pdef – A function that takes a milestone as an argument and returns a collection of other milestones to which a connection attempt must be made. The default connection strategy is to connect a milestone’s 10 closest neighbors.

void setDefaultConnectionStrategy()

Set default strategy for connecting to nearest neighbors

void setMaxNearestNeighbors(unsigned int k)

Convenience function that sets the connection strategy to the default one with k nearest neighbors.

inline void setConnectionFilter(const ConnectionFilter &connectionFilter)

Set the function that can reject a milestone connection.

The given function is called immediately before a connection

is checked for collision and added to the roadmap. Other neighbors may have already been connected before this function is called. This allows certain heuristics that use the structure of the roadmap (like connected components or useful cycles) to be implemented by changing this function.

Parameters:

connectionFilter – A function that takes the new milestone, a neighboring milestone and returns whether a connection should be attempted.

inline unsigned long int milestoneCount() const

Return the number of milestones currently in the graph.

inline unsigned long int edgeCount() const

Return the number of edges currently in the graph.

virtual void getPlannerData(base::PlannerData &data) const override

Get information about the current run of the motion planner. Repeated calls to this function will update data (only additions are made). This is useful to see what changed in the exploration datastructure, between calls to solve(), for example (without calling clear() in between).

virtual void setup() override

Perform extra configuration steps, if needed. This call will also issue a call to ompl::base::SpaceInformation::setup() if needed. This must be called before solving.

virtual void clear() override

Clear all internal datastructures. Planner settings are not affected. Subsequent calls to solve() will ignore all previous work.

virtual void clearQuery() override

Clear the query previously loaded from the ProblemDefinition. Subsequent calls to solve() will reuse the previously computed roadmap, but will clear the set of input states constructed by the previous call to solve(). This enables multi-query functionality for LazyPRM.

void clearValidity()

change the validity flag of each node and edge to VALIDITY_UNKNOWN

virtual base::PlannerStatus solve(const base::PlannerTerminationCondition &ptc) override

Function that can solve the motion planning problem. This function can be called multiple times on the same problem, without calling clear() in between. This allows the planner to continue work for more time on an unsolved problem, for example. If this option is used, it is assumed the problem definition is not changed (unpredictable results otherwise). The only change in the problem definition that is accounted for is the addition of starting or goal states (but not changing previously added start/goal states). If clearQuery() is called, the planner may retain prior datastructures generated from a previous query on a new problem definition. The function terminates if the call to ptc returns true.

Protected Functions

inline std::string getIterationCount() const
inline std::string getBestCost() const
inline std::string getMilestoneCountString() const
inline std::string getEdgeCountString() const
void freeMemory()

Free all the memory allocated by the planner.

Vertex addMilestone(base::State *state)

Construct a milestone for a given state (state), store it in the nearest neighbors data structure and then connect it to the roadmap in accordance to the connection strategy.

void uniteComponents(Vertex a, Vertex b)
void markComponent(Vertex v, unsigned long int newComponent)
long int solutionComponent(std::pair<std::size_t, std::size_t> *startGoalPair) const

Check if any pair of a start state and goal state are part of the same connected component. If so, return the id of that component. Otherwise, return -1.

ompl::base::PathPtr constructSolution(const Vertex &start, const Vertex &goal)

Given two milestones from the same connected component, construct a path connecting them and set it as the solution.

inline double distanceFunction(const Vertex a, const Vertex b) const

Compute distance between two milestones (this is simply distance between the states of the milestones)

base::Cost costHeuristic(Vertex u, Vertex v) const

Given two vertices, returns a heuristic on the cost of the path connecting them. This method wraps OptimizationObjective::motionCostHeuristic.

Protected Attributes

bool starStrategy_

Flag indicating whether the default connection strategy is the Star strategy.

ConnectionStrategy connectionStrategy_

Function that returns the milestones to attempt connections with.

ConnectionFilter connectionFilter_

Function that can reject a milestone connection.

bool userSetConnectionStrategy_ = {false}

Flag indicating whether the employed connection strategy was set by the user (or defaults are assumed)

double maxDistance_ = {0.}

The maximum length of a motion to be added to a tree.

base::StateSamplerPtr sampler_

Sampler user for generating random in the state space.

RoadmapNeighbors nn_

Nearest neighbors data structure.

Graph g_

Connectivity graph.

std::vector<Vertex> startM_

Array of start milestones.

std::vector<Vertex> goalM_

Array of goal milestones.

boost::property_map<Graph, boost::vertex_index_t>::type indexProperty_

Access to the internal base::state at each Vertex.

boost::property_map<Graph, vertex_state_t>::type stateProperty_

Access to the internal base::state at each Vertex.

boost::property_map<Graph, boost::edge_weight_t>::type weightProperty_

Access to the weights of each Edge.

boost::property_map<Graph, vertex_component_t>::type vertexComponentProperty_

Access the connected component of a vertex.

boost::property_map<Graph, vertex_flags_t>::type vertexValidityProperty_

Access the validity state of a vertex.

boost::property_map<Graph, edge_flags_t>::type edgeValidityProperty_

Access the validity state of an edge.

unsigned long int componentCount_ = {0}

Number of connected components created so far. This is used as an ID only, does not represent the actual number of components currently in the graph.

std::map<unsigned long int, unsigned long int> componentSize_

The number of elements in each component in the LazyPRM roadmap.

base::OptimizationObjectivePtr opt_

Objective cost function for PRM graph edges.

base::Cost bestCost_ = {std::numeric_limits<double>::quiet_NaN()}
unsigned long int iterations_ = {0}

Protected Static Attributes

static const unsigned int VALIDITY_UNKNOWN = 0

Flag indicating validity of an edge of a vertex.

static const unsigned int VALIDITY_TRUE = 1

Flag indicating validity of an edge of a vertex.

struct edge_flags_t

Public Types

using kind = boost::edge_property_tag
struct vertex_component_t

Public Types

using kind = boost::vertex_property_tag
struct vertex_flags_t

Public Types

using kind = boost::vertex_property_tag
struct vertex_state_t

Public Types

using kind = boost::vertex_property_tag