Page 13 - DCAP601_SIMULATION_AND_MODELING

Unit 1: Introduction to System Simulation

is to select a goal position that is some distance forward of the vehicle on the path. Pure pursuit Notes
is a type of pursuit curve used in aerial combat in which an aircraft pursues another aircraft by
pointing its nose directly towards it. This is in contrast with lead pursuit, in which the chasing
aircraft points ahead of the aircraft it is following (typically used when attempting a gun attack)
and lag pursuit, in which the chasing aircraft points behind the aircraft it is following (typically
used when attempting a rear-aspect missile attack. The name pure pursuit occurs from the
resemblance that we use to portray the method. We have a tendency to think of the vehicle as
chasing a point on the path some distance ahead of it - it is chasing that moving point. That
analogy is frequently used to evaluate this method to the manner in which humans drives. We
have a propensity to look some distance in front of the car and head in the direction of that spot.
This look ahead distance varies as we drive to reflect the twist of the road and visualization
occlusions.

Pursuit Algorilthm

The execution of the pure pursuit algorithm itself is quite simple. The pure pursuit algorithm
can be summarized as below:

1. Establish the current location of the vehicle.
2. Locate the path point closest to the vehicle.
3. Locate the goal point

4. Convert the goal pole to vehicle coordinates.
5. Compute the curvature and appeal the vehicle to set the routing to that curvature.
6. Update the vehicle’s location.
1. Establish the current location of the vehicle. Both the HMMWV and NavLab have a central
vehicle organizer that offers functions which account the vehicle’s current location as
(x,y,heading). The position is reposed with respect to the vehicle’s location at initialization
time. This original location is the global reference frame for the run.
2. Locate the path point closest to the vehicle. In the geometric origin it was confirmed that
the goal point would be inside one look ahead distane of the vehicle. It is probable that
there are numerous points one look ahead distance from the vehicle’s existing location.
The vehicle should steer toward the closest point one look ahead distance from its existing
location. So, the path point closest to the vehicle will first be establish, and the search for
a point 1 lookahead distance away from the vehicle will start at this point and initiate up
the path.
3. Locate the goal point. The goal point is set up by moving up the path and computing the
distance between that path point and the vehicle’s existing location. Path point positions
are recorded in the global frame; this computation is done in worldwide coordinates.

4. Convert the goal point to vehicle coordinates. Once the goal point has been establish, it
must be converted to the vehicle’s local coordinates. The derivation for the curvature was
performed in vehicle coordinates and curvature commands to the vehicle make sense in
vehicle. coordinates.
5. Compute the curvature. Using the curvature equation, compute the desired vehicle
curvature. The curvature is converted into steering wheel angle by the vehicle’s on board
controller.

6. Update the vehicle’s location. During simulation, it is essential to determine what effects
the command has upon the vehicle’s location and heading.

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