Markers elucidated and applied in local 3-space

The term "marker" as used in the active vision and reactive planning literature is poorly defined. The underspecification of the marker concept limits the usefulness of this important tool for building perception and action systems for autonomous robots. This paper refines the concept of markers, both at the level of their role in perception-action system, and the level of the representations used in their implementation. Our definition encompasses markers in dynamic 3D environments, which are retained even when not in the current perceptual input, either due to occlusion, a limited field of view, or sensing errors. We develop methods for maintaining the representation in the face of these difficulties. The marker concept is further elaborated by a categorization of marker types we have found useful in our research. Relationships among markers are also discussed: relationships which potentially form a link between classical and reactive planning. Finally, we describe a marker-based implementation of an autonomous agent performing search and avoidance tasks in a three-dimensional virtual environment.