# Manipulating Trajectories
Once a trajectory has been generated, you can retrieve information from it using certain methods. These methods will be useful when writing code to follow these trajectories.

## Getting the total duration of the trajectory
Because all trajectories have timestamps at each point, the amount of time it should take for a robot to traverse the entire trajectory is pre-determined. The ``TotalTime()`` (C++) / ``getTotalTimeSeconds()`` (Java) / ``totalTime`` (Python) method can be used to determine the time it takes to traverse the trajectory.


.. tab-set-code::

   ```java
   // Get the total time of the trajectory in seconds
   double duration = trajectory.getTotalTimeSeconds();
   ```

   ```c++
   // Get the total time of the trajectory
   units::second_t duration = trajectory.TotalTime();
   ```

   ```python
   # Get the total time of the trajectory
   duration = trajectory.totalTime()
   ```

## Sampling the trajectory
The trajectory can be sampled at various timesteps to get the pose, velocity, and acceleration at that point. The ``Sample(units::second_t time)`` (C++) / ``sample(double timeSeconds)`` (Java/Python) method can be used to sample the trajectory at any timestep. The parameter refers to the amount of time passed since 0 seconds (the starting point of the trajectory). This method returns a ``Trajectory::Sample`` with information about that sample point.

.. tab-set-code::

   ```java
   // Sample the trajectory at 1.2 seconds. This represents where the robot
   // should be after 1.2 seconds of traversal.
   Trajectory.Sample point = trajectory.sample(1.2);
   ```

   ```c++
   // Sample the trajectory at 1.2 seconds. This represents where the robot
   // should be after 1.2 seconds of traversal.
   Trajectory::State point = trajectory.Sample(1.2_s);
   ```

   ```python
   # Sample the trajectory at 1.2 seconds. This represents where the robot
   # should be after 1.2 seconds of traversal.
   point = trajectory.sample(1.2)
   ```

The ``Trajectory::Sample`` struct has several pieces of information about the sample point:

* ``t``: The time elapsed from the beginning of the trajectory up to the sample point.
* ``velocity``: The velocity at the sample point.
* ``acceleration``: The acceleration at the sample point.
* ``pose``: The pose (x, y, heading) at the sample point.
* ``curvature``: The curvature (rate of change of heading with respect to distance along the trajectory) at the sample point.

Note: The angular velocity at the sample point can be calculated by multiplying the velocity by the curvature.

## Getting all states of the trajectory (advanced)
A more advanced user can get a list of all states of the trajectory by calling the ``States()`` (C++) / ``getStates()`` (Java) / ``states`` (Python) method. Each state represents a point on the trajectory. :ref:`When the trajectory is created <docs/software/advanced-controls/trajectories/trajectory-generation:Generating the trajectory>` using the ``TrajectoryGenerator::GenerateTrajectory(...)`` method, a list of trajectory points / states are created. When the user samples the trajectory at a particular timestep, a new sample point is interpolated between two existing points / states in the list.