Understanding the mc_att_control.cpp for multicopter attitude controller

#1

Hello !
I am trying to understand the mc_att_control.cpp code. What is TPA_RATE and what is the significance of those indexes ?

Apologies for silly questions.

#2

Additionally what is VELD here ?

MulticopterPositionControl::MulticopterPositionControl() :
SuperBlock(nullptr, “MPC”),
ModuleParams(nullptr),
_vel_x_deriv(this, “VELD”),
_vel_y_deriv(this, “VELD”),
_vel_z_deriv(this, “VELD”),
_control(this)
{
// fetch initial parameter values
parameters_update(true);
// set failsafe hysteresis
_failsafe_land_hysteresis.set_hysteresis_time_from(false, LOITER_TIME_BEFORE_DESCEND);
}