Following a Line
As a first example of using Altaira, we will use
reflex-level rules to follow a line without making a map. For this
task, we consider only the three center sensors; the tile marks
detected by the outboard sensors are irrelevant.
As this example requires only reflex-level rules, there will be no
changes in direction or state in the course of the example.
All of the rules shown here are screen dumps taken from an Altaira
session.
No Correction Required
No course correction is required when the only relevant sensor over a
line is the center sensor. In this case, both motors are turned on,
forward. Since either or both outboard sensors may also be on, we
require the following four rules:
Veering to the Side
This situation can be detected if either the left or the right inboard
sensor is dark (the center sensor may be either light or dark; a light
center sensor indicates that the car has veered farther than a dark
sensor). In all cases, we turn off the motor on the side with the
dark inboard sensor. To save space, we will only show the rules for
which the outboard sensors are light (keep in mind that rules are also
required for the cases in which one or both outboard sensors are dark).
Default Rules
Two situations are not covered by the rules described so far: a
situation in which the sensors are not over a line (this may well be a
case in which the line is between the sensors), and the situation in
which all three center sensors are dark (this will occur while the car
is crossing the mark between two tiles, and as a result of the center
line branching in the 3-way and 4-way intersection tiles). One likely
thing to do in these cases is to simply leav both motors on, under the
theory that simply plunging on is as useful a thing to do as any:
Intersections
The ruleset described here is available as line.rs. It
will successfully follow simple lines, but will lose its way when
entering a three-way intersection from the bottom. An alternate
ruleset, which will turn right at intersections (and not get lost),
may be obtained by changing the ``all-white'' default rules to:
Remember, the analogous states with dark outboard sensors are also
required.