Spatial Aggregation : Theory and

Visual thinking plays an important role in scientiic reasoning. Based on the research in automating diverse reasoning tasks about dynamical systems, nonlinear controllers, kine-matic mechanisms, and uid motion, we have identiied a style of visual thinking, imagistic reasoning. Imagistic reasoning organizes computations around image-like, analogue representations so that perceptual and symbolic operations can be brought to bear to infer structure and behavior. Programs incorporating imagistic reasoning have been shown to perform at an expert level in domains that defy current analytic or numerical methods. We have developed a computational paradigm, spatial aggregation, to unify the description of a class of imagistic problem solvers. A program written in this paradigm has the following properties. It takes a continuous eld and optional objective functions as input, and produces high-level descriptions of structure, behavior, or control actions. It computes a multi-layer of intermediate representations, called spatial aggregates, by forming equivalence classes and adjacency relations. It employs a small set of generic operators such as aggregation, classiication, and localization to perform bidirectional mapping between the information-rich eld and successively more abstract spatial aggregates. It uses a data structure, the neighborhood graph, as a common interface to modularize computations. To illustrate our theory, we describe the computational structure of three implemented problem solvers { kam, maps, and hipair | in terms of the spatial aggregation generic operators by mixing and matching a library of commonly used routines.