Master Thesis - Hochschule Bonn-Rhein-Sieg

5. Algorithms Master Thesis Björn Ostermann page 96 of 126
5.5.5 Calculating the shortest evasion path
For safety reasons, the length value in each point of the borderline from the previous chapter (5.5.4) is
reduced by a certain value, effectively increasing the distance the robot has to keep from intruding
objects by creating a safety borderline (see Figure 69a). As described in the outlook of this work
(chapter 7.2), this increase in the safety distance will later be dynamical, dependant on several factors
like the objects current speed and direction of movement.
If the current goal position of the robot is blocked by an intruding object, it is relocated at its given
angle. Its new position is the same as the point of the safety borderline at that angle. This allows the
robot to drive as close to its goal as possible.
As a next step towards the shortest evasion path, all parts of the safety border line that are further away
than the direct path between the current angle and the goal angle are neglected (see Figure 69b). This
safes computational effort in later steps.
a) b)
current angle
goal angle
Figure 69: a) Red safety border line and b) its significant part
current angle
goal angle
To find those parts of the safety borderline that are closer to the robot base’s centre than the direct path
to the goal, the intersections of the line connecting the current position and the goal position and the
line from the centre of the robot to the individual safety borderline-points are computed (see Equation
13).