The critical radius in sampling-based motion planning

Kiril Solovey*, Michal Kleinbort

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


We develop a new analysis of sampling-based motion planning in Euclidean space with uniform random sampling, which significantly improves upon the celebrated result of Karaman and Frazzoli and subsequent work. In particular, we prove the existence of a critical connection radius proportional to Θ(n-1/d) for n samples and d dimensions: below this value the planner is guaranteed to fail (similarly shown by Karaman and Frazzoli). More importantly, for larger radius values the planner is asymptotically (near-)optimal. Furthermore, our analysis yields an explicit lower bound of 1-0(n-1) on the probability of success. A practical implication of our work is that asymptotic (near-)optimality is achieved when each sample is connected to only (log n/n)1/d neighbors. This is in stark contrast to previous work that requires Θ(log n) connections, which are induced by a radius of order Θ(1). Our analysis applies to the probabilistic roadmap method (PRM), as well as a variety of “PRM-based” planners, including RRG, FMT*, and BTT. Continuum percolation plays an important role in our proofs. Lastly, we develop similar theory for all the aforementioned planners when constructed with deterministic samples, which are then sparsified in a randomized fashion. We believe that this new model, and its analysis, is interesting in its own right.

Original languageEnglish
Pages (from-to)266-285
Number of pages20
JournalInternational Journal of Robotics Research
Issue number2-3
StatePublished - 1 Mar 2020


  • Motion planning
  • asymptotic optimality
  • continuum percolation
  • probabilistic completeness
  • probabilistic roadmaps
  • random geometric graphs
  • sampling-based algorithms


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