Task 1: Stationkeeping Practice Worlds

Task 1: Stationkeeping

The three example worlds provided for the Stationkeeping task are as follows:

• stationkeeping0.world: Easy environment.
• stationkeeping1.world: Medium difficulty environment.
• stationkeeping2.world: Hard difficulty environment.

These three worlds all have goals set relatively close to the WAM-V starting position. Due to the nature of the task, they vary primarily in terms of environmental factors.

Development and Debugging Tips

Details of the ROS interface are provided in the VRX competition documents available on the Documentation Wiki.

For all tasks, monitoring the task information will tell you about the task and the current status, e.g.,

rostopic echo /vrx/task/info 
name: "stationkeeping"
state: "running"
ready_time: 
  secs: 10
  nsecs:         0
running_time: 
  secs: 20
  nsecs:         0
elapsed_time: 
  secs: 135
  nsecs:         0
remaining_time: 
  secs: 165
  nsecs:         0
timed_out: False
score: 10.3547826152
---

The goal pose (x, y and yaw) is provided as a ROS topic, e.g.

rostopic echo /vrx/station_keeping/goal
header: 
  seq: 0
  stamp: 
    secs: 10
    nsecs:         0
  frame_id: ''
pose: 
  position: 
    latitude: 21.31085
    longitude: -157.8886
    altitude: 0.0
  orientation: 
    x: 0.0
    y: 0.0
    z: 0.501213004674
    w: 0.865323941623
---

Note that the yaw component of the goal is provided as a quaternion in the ENU coordinate frame (see REP-103). It may be desirable to determine the yaw angle from the quaternion. There are a variety of tools to convert from quaternions to Euler angles. Here is a Python example that uses the ROS tf module:

In [1]: from tf.transformations import euler_from_quaternion

In [2]: # Quaternion in order of x, y, z, w

In [3]: q = (0, 0, 0.501213004674, 0.865323941623)

In [4]: yaw = euler_from_quaternion(q)[2]

In [5]: print yaw
1.05

Note that the yaw angle is in radians, ENU.

You can monitor the instantaneous pose error with

 rostopic echo /vrx/station_keeping/pose_error 

and the cummulative pose error with

rostopic echo /vrx/station_keeping/rms_error  

Note: As discussed in the current VRX Competition and Task Descriptions document, the following ROS API topics are only available for development/debugging, they will not be available to the team's software during scored runs of the competition.

• /vrx/station_keeping/pose_error
• /vrx/station_keeping/rms_error

stationkeeping0.world

stationkeeping1.world

stationkeeping2.world