Page 151 - Designing Autonomous Mobile Robots : Inside the Mindo f an Intellegent Machine

Chapter 9

If the distance between points is too small, the number of points can become unnec-
essarily large, requiring a great deal of memory. Since this path may be transmitted
over our communications system, large files are undesirable from a bandwidth stand-
point as well. The spacing between points is usually within an order of magnitude of
the length of the vehicle, unless they describe a particularly tight geometry.

Smoothest performance can be achieved in following such a path if the rabbit is moved
in smaller increments than the distance between the bread crumbs. This can be done by
simply performing a straight-line segment between each of the bread crumbs.

The Z axis, maps, and wormholes
For outdoor systems, the z axis must be saved for each of the points in a bread crumb
trail if the robot is to operate on anything but a flat surface. Indoors, however, the
robot may need to move from floor-to-floor of a building. It is not enough to save
the z value of each floor, because the floor plans are typically different at each level.
For this reason, instead of a normal z axis, I prefer having the ability to change maps.
In Cybermotion systems, each node has a prefix that is the abbreviation for the map
it belongs to. For example, Flr1_AB is node AB on the Flr1 map. Special “paths”
known as wormholes have nodes that are physically at the same location but that
belong to adjoining maps. In this way, an action from Flr1_AB to Flr2_AC creates
no executable instructions for the robot, but causes the base station to register that
the robot has gone from node AB on the Flr1 map to node AC on the Flr2 map.

An object-oriented approach to the situation is to assign both the value of Z and the
map name as properties of the nodes. Paths between nodes would then inherit these
properties. Nodes can be objects in their own right that are in turn properties of
paths, or they can simply be members of arrays that are properties of paths. The
latter representation will conserve memory while the former is more politically
correct.
There are compelling reasons to maintain multiple map capability, even in outdoor
systems. For one thing, the size of each map can be kept reasonable. Smaller maps
mean faster display, pan, and zoom at the base station. In addition, it is quite pos-
sible that an autonomous vehicle will need to enter a structure such as a parking
garage where multiple maps are essential.

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