feat(pid_longitudinal_controller): update readme

Signed-off-by: Berkay Karaman <brkay54@gmail.com>

Author: brkay54

control/pid_longitudinal_controller/README.md

@@ -55,14 +55,16 @@ For reliable stopping, the target acceleration calculated by the FeedForward sys
 
 Based on the slope information, a compensation term is added to the target acceleration.
 
-There are two sources of the slope information, which can be switched by a parameter.
+There are two sources of the slope information, both sources are used in controller with respect to state of the node.
 
-- Pitch of the estimated ego-pose (default)
+- Pitch of the estimated ego-pose
   - Calculates the current slope from the pitch angle of the estimated ego-pose
+  - It is used only for vehicle in stopped state because of delay compensation.
   - Pros: Easily available
   - Cons: Cannot extract accurate slope information due to the influence of vehicle vibration.
 - Z coordinate on the trajectory
   - Calculates the road slope from the difference of z-coordinates between the front and rear wheel positions in the target trajectory
+  - It is used when the vehicle in drive state because we can get the target slope value from the trajectory.
   - Pros: More accurate than pitch information, if the z-coordinates of the route are properly maintained
   - Pros: Can be used in combination with delay compensation (not yet implemented)
   - Cons: z-coordinates of high-precision map is needed.
@@ -99,23 +101,6 @@ Depending on the actuating principle of the vehicle, the mechanism that physical
 
 In this controller, the predicted ego-velocity and the target velocity after the delay time are calculated and used for the feedback to address the time delay problem.
 
-### Slope compensation
-
-Based on the slope information, a compensation term is added to the target acceleration.
-
-There are two sources of the slope information, which can be switched by a parameter.
-
-- Pitch of the estimated ego-pose (default)
-  - Calculates the current slope from the pitch angle of the estimated ego-pose
-  - Pros: Easily available
-  - Cons: Cannot extract accurate slope information due to the influence of vehicle vibration.
-- Z coordinate on the trajectory
-  - Calculates the road slope from the difference of z-coordinates between the front and rear wheel positions in the target trajectory
-  - Pros: More accurate than pitch information, if the z-coordinates of the route are properly maintained
-  - Pros: Can be used in combination with delay compensation (not yet implemented)
-  - Cons: z-coordinates of high-precision map is needed.
-  - Cons: Does not support free space planning (for now)
-
 ## Assumptions / Known limits
 
 1. Smoothed target velocity and its acceleration shall be set in the trajectory