Page - 77 - in Integration of Advanced Driver Assistance Systems on Full-Vehicle Level - Parametrization of an Adaptive Cruise Control System Based on Test Drives

6.2. ACC Controller Parameter Identification 300 200 100 0 50 10 15 20 25 30 35 40 [m]0s unfiltered filtered Figure 6.6.: Histogram for filtered and unfiltered s0 TTC−1OTF≤0.05s−1. This limit was set according to Moon et al., [MY08]. The TTC is defined by the equation TTCi=−sri sr˙i . (6.11) This describes the time it will take until the i-th object will collide with the ego vehicle, if neither vehicle accelerates or decelerates. According to Fancher et al., the TTC is a good measure for human-like range-rate estimation because humans approximate the relative velocity of any object at big distances by the so-called looming effect, [FBE01]. The looming effect is the change of the size of the projected picture of the object onto the retina of the human eye, see fig. 6.7. The relationh= rα is given forα 1, which is true for r h. The derivative with respect to time reads 0 = r˙α+rα˙. The definition of TTC in eq. (6.12) could be found by rearranging this equation to α α˙ =−r r˙︸︷︷︸ TTC . (6.12) This relations shows why the TTC is a good measure for evaluating the relative velocity as humans would. During constant following, the distance to the OTF should be described by eq. (2.22). To find the missing parameter τset, a least square problem is defined, where the squared error between the measured distance to the object srOTF and eq. (2.22) is minimized. 77