Path Matching

Concept

The path (or trajectory) matching component is responsible for safety checks based on the target trajectory and calculation of the vehicle position in a path-centered coordinate frame. This calculation is done via a closest point search (localTrajectoryMatching.m).

Safety checks

The software employs multiple safety checks:

• The lateral deviation from the path and the heading deviation have to be within certain bounds

• The target trajectory has to respect the dynamic limits (combined acceleration constraints)

• The emergency trajectory has to respect the dynamic limits as well as ending close to zero velocities

• Both trajectories are required to be updated with sufficient frequency

The dynamic limits are calculated based on a diamond-shape (standard setting) constraint as depicted in the figure below:

Details on the computation of those constraints can be found in checkTrajectory.m.

Warning

All safety checks apply during startup as well as during driving. If these criteria are not met, the vehicle either does not start driving or switches to emergency mode.

Tuning

In the following, the basic tuning process is described for all algorithms in this component. Take care that some data dictionaries have vehicle specific version. This is always named e.g. db_xxxxxxxx.sldd. If you change a parameter, you have to do it in the vehicle specific version. This is configured before simulation or building the model automatically by the vehicle project.

Path Matching: xx_mvdc_path_matching.sldd:

The most step in the setup of this algorithm is the correct parametrization of the safety checks. P_VDC_ActivateHighPathDeviationDetection_b activates the checks path deviation checks. P_VDC_LateralPathDeviationMax_m describes the maximum allowed lateral path deviation and P_VDC_HeadingPathDeviationMax_rad the maximum allowed heading deviation. The parametrization of the dynamic limit safety checks is done via P_VDC_axSafetyChecks_mps2 and P_VDC_aySafetyChecks_mps2.

If only cartesian coordinates and a velocity profile is provided to the controller, P_VDC_LocalFFCalculationActive_b must be set to true. This triggers local calculation of the required feedforward information about the path based on numeric derivatives.

Parameter list xx_mvdc_path_matching

This list only serves as a brief description, see the code and the documentation therein for details.

Parameter	Description
P_VDC_LateralPathDeviationMax_m	Maximum admissable lateral path deviation
P_VDC_HeadingPathDeviationMax_rad	Maximum admissable heading path deviation
P_VDC_PathMatchingTimeOut	Maximum admissable time until a new trajectory is expected
P_VDC_CurvatureForesight_s	Foresight time for readout of actual trajectory curvature
P_VDC_PowertrainForesight_s	Foresight time for readout of actual trajectory longitudinal acceleration
P_VDC_LocalFFCalculationActive_b	Recalculate target trajectory accelerations and curvature based on path and velocity profile