feat(time-based-safe-dist): update readme file

Signed-off-by: Ahmed Ebrahim <[email protected]>

planning/autoware_obstacle_cruise_planner/README.md

@@ -200,12 +200,18 @@ If the acceleration is less than `common.min_strong_accel`, the stop planning wi
 
 | Parameter                     | Type   | Description                                    |
 | ----------------------------- | ------ | ---------------------------------------------- |
+| `common.safe_distance_method` | string | safe distance method selection from time_based and RSS |
 | `common.safe_distance_margin` | double | minimum distance with obstacles for cruise [m] |
+| `common.safe_distance_time_margin` | double | time values used in time-based safe distance rule, e.g. 2-seconds rule, 3-seconds rule [s]|
 
 The role of the cruise planning is keeping a safe distance with dynamic vehicle objects with smoothed velocity transition.
 This includes not only cruising a front vehicle, but also reacting a cut-in and cut-out vehicle.
 
-The safe distance is calculated dynamically based on the Responsibility-Sensitive Safety (RSS) by the following equation.
+The parameter `common.safe_distance_method` is used to select the safe distnace method to be either `RSS` or `time-based`.
+
+#### RSS
+
+In Responsibility-Sensitive Safety (RSS) method, the safe distance is calculated dynamically based on the following equation.
 
 $$
 d_{rss} = v_{ego} t_{idling} + \frac{1}{2} a_{ego} t_{idling}^2 + \frac{v_{ego}^2}{2 a_{ego}} - \frac{v_{obstacle}^2}{2 a_{obstacle}},
@@ -242,6 +248,18 @@ $$
 | `lpf(val)`        | apply low-pass filter to `val`          |
 | `pid(val)`        | apply pid to `val`                      |
 
+#### Time-based
+In time-based method, the safe distance is calculated dynamically based on the following equation.
+
+$$
+d_{time,based} = v_{ego} * t_{safe,distance}
+$$
+
+assuming that 
+- $d_{time,based}$ is the calculated safe distance, 
+- $v_{ego}$ is the ego's current velocity, and 
+- $t_{safe,distance}$ is the selected time value time-based safe distance rule, e.g. 2-seconds rule, 3-seconds rule. Parameter: `common.safe_distance_time_margin`
+
 ### Slow down planning
 
 | Parameter                                                         | Type           | Description                                                                                                                                                                                                                                                                                                  |

planning/autoware_obstacle_cruise_planner/config/obstacle_cruise_planner.param.yaml

@@ -15,7 +15,7 @@
       min_object_accel_for_rss: -1.0 # front obstacle's acceleration to calculate RSS distance [m/ss]
       safe_distance_margin : 6.0 # This is also used as a stop margin [m]
       terminal_safe_distance_margin : 3.0 # Stop margin at the goal. This value cannot exceed safe distance margin. [m]
-      safe_distance_time_margin : 2.0 # This is used for time-based safe distance rule, e.g. 2-seconds rule, 3-seconds rules [s]
+      safe_distance_time_margin : 2.0 # This is used for time-based safe distance rule, e.g. 2-seconds rule, 3-seconds rule [s]
       hold_stop_velocity_threshold: 0.01 # The maximum ego velocity to hold stopping [m/s]
       hold_stop_distance_threshold: 0.3 # The ego keeps stopping if the distance to stop changes within the threshold [m]
       slow_down_min_acc: -1.0         # slow down min deceleration [m/ss]