fix(autoware_mpc_lateral_controller): fix calculation method of predicted trajectory

[kyoichi-sugahara]

Description

fix calculation method of predicted trajectory.

As a premise, the MPC optimization result considers a first-order delay applied to the ideal steering angle calculated based on the path curvature.
The original method for calculating the predicted path was as follows:

  // update state in the world coordinate
  const auto updateState = [&](
                             const Eigen::VectorXd & state_w, const Eigen::MatrixXd & input,
                             const double dt, const double velocity) {
    const auto yaw = state_w(2);
    const auto steer = state_w(3);
    const auto desired_steer = input(0);

    Eigen::VectorXd dstate = Eigen::VectorXd::Zero(4);
    dstate(0) = velocity * std::cos(yaw);
    dstate(1) = velocity * std::sin(yaw);
    dstate(2) = velocity * std::tan(steer) / m_wheelbase;
    dstate(3) = -(steer - desired_steer) / m_steer_tau;

    // Note: don't do "return state_w + dstate * dt", which does not work due to the lazy evaluation
    // in Eigen.
    const Eigen::VectorXd next_state = state_w + dstate * dt;
    return next_state;
  };

It calculats the desired steering angle based on the MPC optimization result, and then computed the predicted steering angle at each time step. This approach inadvertently considered the first-order delay twice.
As a result, the following issue occurred:

the predicted path became unstable at low speeds.
In this PR, I confirmed that the problem was resolved by removing the term that considers the steering's first-order delay during the predicted path calculation.

Related links

Parent Issue:

• Link

How was this PR tested?

• run psim
• passed TIERIV INTERNAL SCENARIOS

Notes for reviewers

None.

Interface changes

None.

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 26.67%. Comparing base (d4d40cd) to head (bac3f5b).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9048      +/-   ##
==========================================
- Coverage   26.68%   26.67%   -0.01%     
==========================================
  Files        1296     1296              
  Lines       95679    95692      +13     
  Branches    39078    39081       +3     
==========================================
- Hits        25530    25527       -3     
- Misses      67494    67509      +15     
- Partials     2655     2656       +1     

Flag	Coverage Δ		*Carryforward flag
differential	33.11% <100.00%> (?)
total	26.67% <ø> (-0.01%)	⬇️	Carriedforward from d4d40cd

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