An Example in Smart-AHS: Racetrack

I. Introduction

A racetrack of four sections, and (3 + 4 + 1 + 4 =) 12 segments is created as described in Figure 1 is given in file track.hs. There are three lanes in each segment/section.

The letters 'LL', 'RL', 'RU', and 'LU' describe respectively the lower left, lower right, upper right, and upper left sections of the highway. Values 'lw' and 'sl' are the width of the lanes, and length of the section. See file 'track.hs' for details.


Figure 1. The racetrack.

A massless vehicle/object is used to check the definitions in the highway description file defined above. The object controller uses the value 'lyp' (lane position) as input to evaluate the position error, and detemines the necessary steering (or rotation) to track the center of the lane. A PI controller is used, and therefore, there will a steady state error while tracking the curves. (Also, the P and I gains can be adjusted to obtain a better response.) The details can be found in file 'ufo.hs'.

NOTE: This simulation also requires the Smart-AHS files 'highway.hs' and 'vrep.hs'. The type Ufo in file 'ufo.hs' does not include a statement to stop VREP from exiting; you need at this to your copy, or remove transiton all -> exit from 'vrep.hs'.

2. Simulation results

Figure 2 below shows the result of a simulation run for a vehicle in the leftmost (inner) lane (See file track.hs for details).

Note that the phase plot given in Figure 2 has positive y-axis pointing upwards, therfore resulting in a trajectory in clockwise direction. However, the actual trajectory is in the counter clockwise direction due to the definition of the global axis.


Figure 2.The result of the simulation run: the trajectory of the vehicle in the leftmost lane.

• track.hs
• ufo.hs
• Smart-AHS files vrep.hs, highway.hs, and weather.hs as well as external function definitions for Smart-AHS (ext-functions.hs?).

• Figure 3 shows the TkShift animation window for the simulation. The information on adding this window to TkShift GUI is here.

1. A. Deshpande, D. Godbole, A. Gollu, L. Semenzato, R. Sengupta, D. Swaroop and P. Varaiya, "Automated Highway Systems Tool Interface Format," PATH Report, 1996.
   
   
2. California PATH Smart AHS, http://www.path.berkeley.edu/smart-ahs, California PATH (June 1997).
   
   
3. C. Ünsal, A. Göllü, "Coordinate Frames in Smart-AHS," http://www.cs.cmu.edu/~unsal/research/coordinate_frames.html, June 1997.

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Cem Ünsal
Last modified on December 3, 1997