Planning to Chronicle: Optimal Policies for Narrative Observation of Unpredictable Events

Hazhar Rahmani and Dylan A. Shell and Jason M. O'Kane
International Journal of Robotics Research

Abstract An important class of applications entails a robot scrutinizing, monitoring, or recording the evolution of an uncertain time-extended process. This sort of situation leads to an interesting family of active perception problems that can be cast as planning problems in which the robot is limited in what it sees and must, thus, choose what to pay attention to. The distinguishing characteristic of this setting is that the robot has influence over what it captures via its sensors, but exercises no causal authority over the process evolving in the world. As such, the robot's objective is to observe the underlying process and to produce a `chronicle' of occurrent events, subject to a goal specification of the sorts of event sequences that may be of interest. This paper examines variants of such problems in which the robot aims to collect sets of observations to meet a rich specification of their sequential structure. We study this class of problems by modeling a stochastic process via a variant of a hidden Markov model, and specify the event sequences of interest as a regular language, developing a vocabulary of `mutators' that enable sophisticated requirements to be expressed. Under different suppositions about the information gleaned about the event model, we formulate and solve different planning problems. The core underlying idea is the construction of a product between the event model and a specification automaton. Using this product, we compute a policy that minimizes the expected number of steps to reach a goal state. We introduce a general algorithm for this problem as well as several more efficient algorithms for important special cases. The paper reports and compares performance metrics by drawing on some small case studies analyzed in depth in simulation. Specifically, we study the effect of the robot's observation model on the average time required for the robot to record a desired story. We also compare our algorithm with a baseline greedy algorithm, showing that our algorithm outperforms the greedy algorithm in terms of the average time to record a desired story. In addition, our experiments show that the proposed algorithms for the special inputs of the problem are more efficient than the general algorithm.

  author = {Hazhar Rahmani and Dylan A. Shell and Jason M. O'Kane},
  journal = {International Journal of Robotics Research},
  title = {Planning to Chronicle: Optimal Policies for Narrative
           Observation of Unpredictable Events},
  year = {2022}

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