Mars Autonomy Project Integration

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Overview
The Mars Autonomy Project unifies a stereo vision module, a mapping module, local obstacle avoidance, path planning, and low-level control. Each of these modules is a major piece of software in its own right, and they were developed in the context of several projects over the past decade. Designing and implementing a system that includes them all is the major challenge of the project.

 

Architecture
Software Architecture Diagram

 

The diagram above shows our system architecture when we run on the Bullwinkle rover test bed. The red ovals are hardware, and the green rectangles are modules. Each module runs as a separate process (on a separate machine if necessary), and the links shown between modules represent network messages.

We also have the ability to run in two other modes which do not require the rover:

  1. Simulator mode. In this mode, our simulator accepts commands from the controller and returns pose. It also sends range points to the Stereo Map traversability mapper (we bypass the stereo algorithm in order to avoid the overhead of generating simulated stereo image pairs).

  2. Series-reader mode. In this mode, we replay a previously recorded series of stereo pairs to the system. Each pair is stamped with the pose at the time it was recorded. Low-level commands from the controller are ignored (in this case there is no way to simulate their effects).

 
Arbiter
The arbiter, developed over the past several years, is responsible for collecting asynchronous votes from the different modules which have a say in high-level control of the rover, then choosing the best action based on those votes.

In our case, the possible actions are forward moves with different curvatures to the left and right. We also have the ability to turn in place, either left or right. The two voting modules are the local obstacle avoidance and global path planning systems.

Each voting module assigns either a veto or a vote between 0 and 1 to each command. This vote is multiplied by the module's weight in the arbiter. The unvetoed command with the highest weighted sum is sent to the controller.

Many of the arbiter's capabilities, such as smoothing in the time domain and interpolating in between the discrete voting bins to achieve finer control, were developed for other projects and go unused in our system. Most useful to us among its advanced features is a GUI which allows us to visualize the votes coming in from each module for debugging.

 

Networking
We use the Real-Time Communications (RTC) package developed at Carnegie Mellon's National Robotics Engineering Consortium (NREC).

In RTC, the locations of individual modules are tracked by a central server. Modules can register and unregister on the fly. Once the location of the recipient is known to the sender, messages are passed point-to-point. The system supports a limited form of publish-subscribe communication.

Visit the RTC web site.

 


Last modified: $Date: 1999/06/28 18:04:26 $