SBPL overview

This tutorial will describe how SBPL is set up. For background information, click here.

Environments

As described in the previous tutorial, planning with search-based methods have two parts - representing the problem as a graph, then solving the graph with graph-search methods. SBPL has two objects it uses for these two roles - the environment and the planner. Unless you're fiddling with the actual graph search algorithm, the environment object will be the thing you interact most with.

In a nutshell, the environment handles domain specific details and translates them into a generic form for the planner to handle. For example, the environment handles the translation between the (x, y, theta) position of a robot into a graph composed of generic state IDs. The planner then solves the graph without having to know about the domain. (This doesn't actually happen in one step - the graph is generated on demand by the planner. As a result, the planner often calls the environment object to retrieve information on demand). 

The environment also implements the heuristic computation. This is domain dependent, since the heuristic for guiding a robotic arm to an object will be different from navigating a car close to its goal.

There already exists many environments and planners in SBPL, but they might not cover a custom scenario. In this case, you will have to implement your own environment (a very involved topic that might be covered in the future).

  • Environment2D - for robots navigating in (x, y) coordinates
  • EnvironmentXYTHETALAT - for robots navigating in (x, y, theta) coordinates
  • EnvironmentXYTHETALEVLAT - for robots navigating in (x, y, theta) but alsohandles collision checking and cost computations for a given set of footprints.
  • Environment_robarm - motion planning for a 7D (7 joint angles) robotic arm.

These can all be found in sbpl/src/discrete_space_information.

Other environments that have successfully been implemented (but not included in SBPL): 

  •     pushing a cart with the PR2 (x, y, theta, theta of the cart)
  •     opening a door with the PR2 (x, y, theta, door interval)
  •     quadrotor path planning (x, y, z)
  •     time dependent planning (x, y, z, time)

Planners

There are a number of planners that are available in sbpl/src/planners

  •     ARA*
  •     Anytime D*
  •     R*