📝 Remove wrong information about trajectory replacement (#1979)

(cherry picked from commit cdcacb5)

Author: christophfroehlich

joint_trajectory_controller/doc/trajectory.rst

@@ -109,60 +109,7 @@ To visualize the difference of the different interpolation methods and their inp
 
 Trajectory Replacement
 ---------------------------------
-*Parts of this documentation were originally published in the ROS 1 wiki under the* `CC BY 3.0 license <https://creativecommons.org/licenses/by/3.0/>`_. [#f1]_
-
 Joint trajectory messages allow to specify the time at which a new trajectory should start executing by means of the header timestamp, where zero time (the default) means "start now".
 
-The arrival of a new trajectory command does not necessarily mean that the controller will completely discard the currently running trajectory and substitute it with the new one.
-Rather, the controller will take the useful parts of both and combine them appropriately, yielding a smarter trajectory replacement strategy.
-
-The steps followed by the controller for trajectory replacement are as follows:
-
-  + Get useful parts of the new trajectory: Preserve all waypoints whose time to be reached is in the future, and discard those with times in the past.
-    If there are no useful parts (ie. all waypoints are in the past) the new trajectory is rejected and the current one continues execution without changes.
-
-  + Get useful parts of the current trajectory: Preserve the current trajectory up to the start time of the new trajectory, discard the later parts.
-
-  + Combine the useful parts of the current and new trajectories.
-
-The following examples describe this behavior in detail.
-
-The first example shows a joint which is in hold position mode (flat grey line labeled *pos hold* in the figure below).
-A new trajectory (shown in red) arrives at the current time (now), which contains three waypoints and a start time in the future (*traj start*).
-The time at which waypoints should be reached (``time_from_start`` member of ``trajectory_msgs/JointTrajectoryPoint``) is relative to the trajectory start time.
-
-The controller splices the current hold trajectory at time *traj start* and appends the three waypoints.
-Notice that between now and *traj start* the previous position hold is still maintained, as the new trajectory is not supposed to start yet.
-After the last waypoint is reached, its position is held until new commands arrive.
-
-.. image:: new_trajectory.png
-  :alt: Receiving a new trajectory.
-
-|
-
-The controller guarantees that the transition between the current and new trajectories will be smooth. Longer times to reach the first waypoint mean slower transitions.
-
-The next examples discuss the effect of sending the same trajectory to the controller with different start times.
-The scenario is that of a controller executing the trajectory from the previous example (shown in red),
-and receiving a new command (shown in green) with a trajectory start time set to either zero (start now),
-a future time, or a time in the past.
-
-.. image:: trajectory_replacement_future.png
-  :alt: Trajectory start time in the future.
-
-|
-
-.. image:: trajectory_replacement_now.png
-  :alt: Zero trajectory start time (start now).
-
-|
-
-Of special interest is the last example, where the new trajectory start time and first waypoint are in the past (before now).
-In this case, the first waypoint is discarded and only the second one is realized.
-
-.. image:: trajectory_replacement_past.png
-  :alt: Trajectory start time in the past.
-
-|
-
-.. [#f1] Adolfo Rodriguez: `Understanding trajectory replacement <http://wiki.ros.org/joint_trajectory_controller/UnderstandingTrajectoryReplacement>`_
+The current implementation just forgets the old trajectory.
+Follow this `issue <https://github.com/ros-controls/ros2_controllers/issues/84#issuecomment-2940787997>`__ for more information.