What does filter use for joint_trajectory_action_controller

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Hi,

I am reading joint_trajectory_action_controller.cpp in robot_mechanism_controllers. Following code is about output filter setup.

// Output filters
output_filters_.resize(joints_.size());
for (size_t i = 0; i < joints_.size(); ++i)
{
  std::string p = "output_filters/" + joints_[i]->joint_->name;
  if (node_.hasParam(p))
  {
    output_filters_[i].reset(new filters::FilterChain<double>("double"));
    if (!output_filters_[i]->configure(node_.resolveName(p)))
      output_filters_[i].reset();
  }
}

What does filter use for the controller?

Thanks for any help in advance!