# 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 predetermined. The`getTotalTimeSeconds()`method can be used to determine the time it takes to traverse the trajectory.

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

## Sampling the Trajectory

The trajectory can be sampled at various timesteps to get the pose, velocity, and acceleration at that point. The `sample(double timeSeconds)` 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).

```java
// 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);
```

The sample 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.


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