Details on the Navigation System
The overall navigation software system is divided into on-board and
off-board components, communicating via two radio links for video and
data (eventually, many of the off-board processes will be moved
on-board). The basic data flow is that the stereo process produces terrain
elevation maps which are passed to the obstacle avoidance planner which uses
them to evaluate the efficacy of traveling along different paths.
These recommendations are merged (in semi-autonomous mode) with the
desires of a human operator to
choose the best path to traverse (in autonomous mode, there is
typically no operator input). The command
arbiter then forwards steering and velocity commands to the off-board controller, which packages
them up and ships them, using the RCP
protocol developed at Sandia
Laboratories, to the on-board
controller which then executes the commands and returns status and
Concurrency is very important in achieving the levels of performance
needed (1-2 Hz cycle time is desirable). In particular, perception and
planning functions run simultaneously: while the obstacle avoidance
planner is using one stereo elevation map to evaluate paths, the
stereo system is processing another image. When stereo completes, it
asynchronously sends the image to the planner. Likewise, the arbiter
is getting asynchronous path evaluations from the planner and user
interface, combining the most recent information to produce steering
commands. Meanwhile, the controller module is receiving asynchronous
commands and requests for pose information from different modules.
While it is admittedly more difficult to develop and debug
distributed, concurrent systems, they have great advantages in terms
of real-time performance and modularity in design and implementation.
LRD Navigation Group - email@example.com (last updated in March 1995)
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