Page 154 - Sensing, Intelligence, Motion : How Robots and Humans Move in an Unstructured World

WHICH ALGORITHM TO CHOOSE? 129

Obstacle

S T

Figure 3.24 In this scene, the path generated by an algorithm with vision would be
almost identical to the path generated by a “tactile” planning algorithm.

With more opportunistic algorithms, like VisBig-22, even this property breaks
down: While paths that algorithm VisBig-22 generates are often significantly
shorter than paths produced by algorithm Bug2, this cannot be guaranteed (com-
pare Figures 3.13 and 3.21).
2. Does better vision (a larger radius of vision, r v ) guarantee better perfor-
mance compared to an inferior vision (a smaller radius of vision)? We know
already that for VisBug-22 this is definitely not so—a larger radius of vision
does not guarantee shorter paths (compare Figures 3.21 and 3.14). Interestingly,
even for a more stable VisBug-21, it is not so. The example in Figure 3.25 shows
that, while VisBug-21 always does better with vision than with tactile sensing,
more vision—that is, a larger r v —does not necessarily buy better performance.
In this scene the robot will produce a shorter path when equipped with a smaller
radius of vision (Figures 3.25a) than when equipped with a larger radius of vision
(Figures 3.25b).
The problem lies, of course, in the fundamental properties of uncertainty. As
long as some, even a small piece, of relevant information is missing, anything
may happen. A more experienced hiker will often find a shorter path, but once in a
while a beginner hiker will outperform an experienced hiker. In the stock market,
an experienced stock broker will usually outperform an amateur investor, but once
9
in a while their luck will reverse. In situations with uncertainty, more experience
certainly helps, but it helps only on the average, not in every single case.

9 On a quick glance, the same principle seems to apply to the game of chess, but it does not. Unlike
in other examples above, in chess the uncertainty comes not from the lack of information—complete
information is right there on the table, available to both players—but from the limited amount of
information that one can process in limited time. In a given time an experienced player will check
more candidate moves than will a novice.