Collaboration diagram for Algorithm Abstractions:

Modules
	Distance Metrics
	Distance Metrics (DM) compute distances between two configurations.

	Validity Checkers
	Validity Checkers (VC) determine if a configuration is in $\mathcal{C}_{free}$ or $\mathcal{C}_{obst}$ .

	Samplers
	Samplers (S) generate configurations in $\mathcal{C}_{space}$ (usually $\mathcal{C}_{free}$ ).

	Neighborhood Finders
	Neighborhood Finders (NF) determine nearest neighbors within a roadmap.

	Local Planners
	Local Plannners (LP) validate simple, often deterministic paths, between configurations.

	Extenders
	Extenders (E) step configurations toward a direction until an end condition is met, e.g., a distance $\Delta q$ is reached.

	Connectors
	Connectors (C) generate edges of a roadmap, usually a combination of a neighborhood finder and a local planner.

	Metrics
	Metrics (M) determine a value/property from a roadmap.

	Map Evaluators
	Map Evaluators (ME) determine if a roadmap passes an evaluation test, e.g., can solve an example query.

	Path Modifiers
	Path Modifiers (PM) smooth/modify an input path to produce a new valid path.

	Region Decomposition
	Region framework to split space for divide and conquer methods.

	Motion Planning Strategies
	Motion Planning Strategies (MPS) loosely, construct a roadmap, but more generally are anything executable by PPL, e.g., solve this problem or smooth this path.

Detailed Description

The algorithm abstractions in PPL are:

Distance Metrics - Compute distances between two configurations
Validity Checkers - Determine if a configuration is in $\mathcal{C}_{free}$ or $\mathcal{C}_{obst}$
Samplers - Generate configurations in $\mathcal{C}_{space}$ (usually $\mathcal{C}_{free}$ )
Neighborhood Finders - Determine nearest neighbors within a roadmap
Local Planners - Validate simple, often deterministic paths, between configurations
Extenders - Step configurations toward a direction until an end condition is met, e.g., a distance $\Delta q$ is reached
Connectors - Generate edges of a roadmap, usually a combination of a neighborhood finder and a local planner
Metrics - Determine a value/property from a roadmap
Map Evaluators - Determine is a roadmap passes an evaluation test, e.g., can solve an example query
Path Modifiers - Smooth/modify an input path to produce a new valid path.
Region Decomposition - Region framework to split space for divide and conquer methods
Motion Planning Strategies - Loosely, construct a roadmap, but more generally are anything executable by PPL, e.g., solve this problem or smooth this path

Modules