They are also the only signs which are, aside for text, all red. A driving system which needs to know whether there is a stop sign at an intersection might be able to only look for a red octagonal shape to the right side of the road. Here, an octagonal shape over a predominantly red and white color region are simple features which can be cheaply detected by a vision system, allowing a designer to construct a simple yet effective mechanism. Initially, I was just trying to get Shopper to look at signs and search aisles for a sought item. In addressing this problem, I roughly divided work into action selection and perception .
Action selection has to do with figuring out what to do now in order to accomplish tasks.
Perception has to do with figuring out what to look at, and where to look. In response, I built a simple plan execution system based on the Runner and RAPs systems. Essentially, Shopper executes hierarchical plans which check the state of the world and recursively enable other plans. For example, the basic search plan for Shopper is to go to the end of an aisle, and then start moving across aisles until it sees a relevant sign. If Shopper ends up back where it started, it knows that that plan didn't work.