CoM task in mc_rtc

[Saeed-Mansouri]

Hi Dr. Caron,

I added a new PositionTask to control pelvis position in the z-direction to have more natural walking. Also, I changed dimweight of CoMTask to {0.5, 1., 0.} and {0., 0., 1.} was set for the new PositionTask. However, I found that the third array of "com" element in the CoMTask of gui didn't change at all. I tried to find that what value returned for "com" element.

void CoMTask::addToGUI(mc_rtc::gui::StateBuilder & gui)
{
  TrajectoryTaskGeneric<tasks::qp::CoMTask>::addToGUI(gui);
  gui.addElement({"Tasks", name_},
                 mc_rtc::gui::Point3D("com_target", [this]() { return this->com(); },
                                      [this](const Eigen::Vector3d & com) { this->com(com); }),
                 mc_rtc::gui::Point3D("com", [this]() { return (this->com() - this->eval()).eval(); }));
}

As you can see below, it seems that this->eval() returns a cross-product of the com error and dimweight. However, I couldn't understand the physical interpretation of this process. I will appreciate it if you could explain it.

template<typename T>
Eigen::VectorXd TrajectoryTaskGeneric<T>::eval() const
{
  if(selectorT_)
  {
    return selectorT_->eval().cwiseProduct(trajectoryT_->dimWeight());
  }
  return errorT->eval().cwiseProduct(trajectoryT_->dimWeight());
}

[stephane-caron]

This question is related to mc_rtc. Continuing the discussion in the mc_rtc issue tracker.