Feed forward position setpoint offset

PX4 Autopilot Multicopter 🛸
1

at mc_pos_control_main.cpp ，void MulticopterPositionControl::control_auto(float dt):

/* feed forward position setpoint offset */
math::Vector<3> pos_ff = prev_curr_s_norm *
			 cos_a_curr_next * cos_b * cos_b * (1.0f - curr_pos_s_len) *
			 (1.0f - expf(-curr_pos_s_len * curr_pos_s_len * 20.0f));
pos_sp_s += pos_ff;

What is the principle of this algorithm? Is there any relevant paper on this algorithm?

thanks.