Recognizing scenes with hierarchical Implicit Shape Models based on spatial object relations for Programming by Demonstration

Abstract

We present an approach for recognizing scenes, consisting of spatial relations between objects, in unstructured indoor environments, which change over time. Object relations are represented by full six Degree-of-Freedom (DoF) coordinate transformations between objects. They are acquired from object poses that are visually perceived while people demonstrate actions that are typically performed in a given scene. We recognize scenes using an Implicit Shape Model (ISM) that is similar to the Generalized Hough Transform. We extend it to take orientations between objects into account. This includes a verification step that allows us to infer not only the existence of scenes, but also the objects they are composed of. ISMs are restricted to represent scenes as star topologies of relations, which insufficiently approximate object relations in complex dynamic settings. False positive detections may occur. Our solution are exchangeable heuristics for recognizing object relations that have to be represented explicitly in separate ISMs. Object relations are modeled by the ISMs themselves. We use hierarchical agglomerative clustering, employing the heuristics, to construct a tree of ISMs. Learning and recognition of scenes with a single ISM is naturally extended to multiple ISMs.