Class LBKPIECE1

Nested Relationships

Nested Types

Inheritance Relationships

Base Type

Class Documentation

class LBKPIECE1 : public ompl::base::Planner

Lazy Bi-directional KPIECE with one level of discretization.

Short description

KPIECE is a tree-based planner that uses a discretization (multiple levels, in general) to guide the exploration of the continuous space. This implementation is a simplified one, using a single level of discretization: one grid. The grid is imposed on a projection of the state space. When exploring the space, preference is given to the boundary of this grid. The boundary is computed to be the set of grid cells that have less than 2n non-diagonal neighbors in an n-dimensional projection space. It is important to set the projection the algorithm uses (setProjectionEvaluator() function). If no projection is set, the planner will attempt to use the default projection associated to the state space. An exception is thrown if no default projection is available either. This variant of the implementation use two trees of exploration with lazy collision checking, hence the LB prefix.

External documentation

  • I.A. Şucan and L.E. Kavraki, Kinodynamic motion planning by interior-exterior cell exploration, in Workshop on the Algorithmic Foundations of Robotics, Dec. 2008.[PDF]

  • R. Bohlin and L.E. Kavraki, Path planning using lazy PRM, in Proc. 2000 IEEE Intl. Conf. on Robotics and Automation, pp. 521–528, 2000. DOI: 10.1109/ROBOT.2000.844107[PDF]

Public Functions

LBKPIECE1(const base::SpaceInformationPtr &si)

Constructor.

~LBKPIECE1() override
inline void setProjectionEvaluator(const base::ProjectionEvaluatorPtr &projectionEvaluator)

Set the projection evaluator. This class is able to compute the projection of a given state.

inline void setProjectionEvaluator(const std::string &name)

Set the projection evaluator (select one from the ones registered with the state space).

inline const base::ProjectionEvaluatorPtr &getProjectionEvaluator() const

Get the projection evaluator.

inline void setRange(double distance)

Set the range the planner is supposed to use.

This parameter greatly influences the runtime of the algorithm. It represents the maximum length of a motion to be added in the tree of motions.

inline double getRange() const

Get the range the planner is using.

inline void setBorderFraction(double bp)

Set the fraction of time for focusing on the border (between 0 and 1). This is the minimum fraction used to select cells that are exterior (minimum because if 95% of cells are on the border, they will be selected with 95% chance, even if this fraction is set to 90%)

inline double getBorderFraction() const

Get the fraction of time to focus exploration on boundary.

inline void setMinValidPathFraction(double fraction)

When extending a motion, the planner can decide to keep the first valid part of it, even if invalid states are found, as long as the valid part represents a sufficiently large fraction from the original motion. This function sets the minimum acceptable fraction.

inline double getMinValidPathFraction() const

Get the value of the fraction set by setMinValidPathFraction()

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 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.

virtual void clear() override

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

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).

Protected Functions

void freeMotion(Motion *motion)

Free the memory for a motion.

void removeMotion(Discretization<Motion> &disc, Motion *motion)

Remove a motion from a tree of motions.

bool isPathValid(Discretization<Motion> &disc, Motion *motion, base::State *temp)

Since solutions are computed in a lazy fashion, once trees are connected, the solution found needs to be checked for validity. This function checks whether the reverse path from a given motion to a root is valid. If this is not the case, invalid motions are removed

Protected Attributes

base::StateSamplerPtr sampler_

The employed state sampler.

base::ProjectionEvaluatorPtr projectionEvaluator_

The employed projection evaluator.

Discretization<Motion> dStart_

The start tree.

Discretization<Motion> dGoal_

The goal tree.

double minValidPathFraction_ = {0.5}

When extending a motion, the planner can decide to keep the first valid part of it, even if invalid states are found, as long as the valid part represents a sufficiently large fraction from the original motion.

double maxDistance_ = {0.}

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

RNG rng_

The random number generator.

std::pair<base::State*, base::State*> connectionPoint_ = {nullptr, nullptr}

The pair of states in each tree connected during planning. Used for PlannerData computation.

class Motion

Representation of a motion for this algorithm.

Public Functions

Motion() = default
inline Motion(const base::SpaceInformationPtr &si)

Constructor that allocates memory for the state.

~Motion() = default

Public Members

const base::State *root = {nullptr}

The root state (start state) that leads to this motion.

base::State *state = {nullptr}

The state contained by this motion.

Motion *parent = {nullptr}

The parent motion in the exploration tree.

bool valid = {false}

Flag indicating whether this motion has been checked for validity.

std::vector<Motion*> children

The set of motions descending from the current motion.