vrx_classic_changing_wave_params_tutorial

Changing the Wave Field

In this example we'll walk through running a simulation with different wave scenarios.

Default wave parameters

The wave field characteristics are defined in the wave_gazebo/world_models/ocean_waves/model.xacro file.

• This file defines the ocean_waves XML macro that is used to add the ocean model to a Gazebo world.
• Changing default parameter values in this file will change the default wave conditions for the simulation.

Below is an excerpt showing the macro definition with five optional input parameters and their default values:

 <xacro:macro name="ocean_waves" params="gain:=0.1 period:=5
                     direction_x:=1.0 direction_y:=0.0
                     angle:=0.4">

The following excerpt from the vrx_gazebo/worlds/example_course.world.xacro file shows an example of how to use this macro in a world file with the default input parameters:

    <!--Waves-->
    <xacro:include filename="$(find wave_gazebo)/world_models/ocean_waves/model.xacro"/>
    <xacro:ocean_waves/>

Changing wave parameters

To change the wind plugin parameters we can do any combination of the following:

• Change the default wave parameters in the wave_gazebo/world_models/ocean_waves/model.xacro file.
• Override the default parameters when calling the macro locally in a world file.

Flat ocean example

Consider the case where we are testing a new algorithm and want to start with a flat ocean (no waves) before adding wave-induced motion. We could accomplish this in two ways:

Option 1: Change global default parameters.

Edit the wave_gazebo/world_models/ocean_waves/model.xacro file, changing the gain value to zero, so it looks like this.

 <xacro:macro name="ocean_waves" params="gain:=0.0 period:=5
                     direction_x:=1.0 direction_y:=0.0
                     angle:=0.4">

Now the value of the gain parameter will be zero for any world that uses the macro without explicitly setting the gain parameter. Consequently, all the wave amplitudes will be zero - a flat ocean. Note, you will need to run catkin_make so that the changes take effect.

Option 2: Change local parameters.

A second option is to explicitly set the parameters when calling the macro. For example, edit the vrx_gazebo/worlds/example_course.world.xacro to set the gain parameter to zero when calling the macro:

  <!--Waves-->
    <xacro:include filename="$(find wave_gazebo)/world_models/ocean_waves/model.xacro"/>
    <xacro:ocean_waves gain="0.0"/>

Then execute catkin_make and start vrx.launch (which uses the example_course world):

catkin_make 
roslaunch vrx_gazebo vrx.launch

This will bring up a simulation envirornment in which the ocean waves all have zero amplitude.

Further testing applications

Ideally, solutions would be tested over the range of possible seastate parameters - see current version of the VRX Technical Guide for the envelope of values which used in the VRX challenge.

• After testing in zero seastate, we may want to stress our algorithm by increasing the seastate.
• This can be accomplished by increasing the gain and/or peak period of the wave spectrum.
• We may also want to test with different wave directions to make sure that a particular solution isn't dependent on a particular wave direction.

We've posted a video showing how we would test with three different seastates - including how to break a buoy!

See also:

Changing the Wind

Changing Fog and Ambient Lighting