update DH names + notes for MPC output curvatures (commaai#24701)

* update names + notes for MPC outputs

"current_curvature" is not the correct description of what the MPC is outputting in it's curvature_ego state.
The MPC is integrating it's free variable, curvature_rate, such that curvature[0] is actually the desired_curvature before any delay.
inversely: the curvature_rate_desired is the desired rate of change to the setpoint and not the actual curvature rate. 

If we were to set the initial curvature = measured curvature in the MPC initiation these names would be correct. 
This was possibly how it was initially set up but the nomenclature here is now confusing.

* more notes

* match

* Clarify #1

selfdrive/controls/lib/drive_helpers.py

@@ -97,26 +97,27 @@ def get_lag_adjusted_curvature(CP, v_ego, psis, curvatures, curvature_rates):
     psis = [0.0]*CONTROL_N
     curvatures = [0.0]*CONTROL_N
     curvature_rates = [0.0]*CONTROL_N
-
+  v_ego = max(v_ego, 0.1)
+
   # TODO this needs more thought, use .2s extra for now to estimate other delays
   delay = CP.steerActuatorDelay + .2
-  current_curvature = curvatures[0]
-  psi = interp(delay, T_IDXS[:CONTROL_N], psis)
-  desired_curvature_rate = curvature_rates[0]
-
+
   # MPC can plan to turn the wheel and turn back before t_delay. This means
   # in high delay cases some corrections never even get commanded. So just use
   # psi to calculate a simple linearization of desired curvature
-  curvature_diff_from_psi = psi / (max(v_ego, 1e-1) * delay) - current_curvature
-  desired_curvature = current_curvature + 2 * curvature_diff_from_psi
-
-  v_ego = max(v_ego, 0.1)
+  current_curvature_desired = curvatures[0]
+  psi = interp(delay, T_IDXS[:CONTROL_N], psis)
+  average_curvature_desired = psi / (v_ego * delay)
+  desired_curvature = 2 * average_curvature_desired - current_curvature_desired
+
+  # This is the "desired rate of the setpoint" not an actual desired rate
+  desired_curvature_rate = curvature_rates[0]
   max_curvature_rate = MAX_LATERAL_JERK / (v_ego**2)
   safe_desired_curvature_rate = clip(desired_curvature_rate,
                                           -max_curvature_rate,
                                           max_curvature_rate)
   safe_desired_curvature = clip(desired_curvature,
-                                     current_curvature - max_curvature_rate * DT_MDL,
-                                     current_curvature + max_curvature_rate * DT_MDL)
+                                     current_curvature_desired - max_curvature_rate * DT_MDL,
+                                     current_curvature_desired + max_curvature_rate * DT_MDL)
 
   return safe_desired_curvature, safe_desired_curvature_rate

selfdrive/controls/lib/latcontrol_indi.py

@@ -78,6 +78,7 @@ def update(self, active, CS, VM, params, last_actuators, desired_curvature, desi
     steers_des += math.radians(params.angleOffsetDeg)
     indi_log.steeringAngleDesiredDeg = math.degrees(steers_des)
 
+    # desired rate is the desired rate of change in the setpoint, not the absolute desired curvature
     rate_des = VM.get_steer_from_curvature(-desired_curvature_rate, CS.vEgo, 0)
     indi_log.steeringRateDesiredDeg = math.degrees(rate_des)
 

selfdrive/controls/lib/latcontrol_torque.py

@@ -59,6 +59,8 @@ def update(self, active, CS, VM, params, last_actuators, desired_curvature, desi
         actual_curvature_llk = llk.angularVelocityCalibrated.value[2] / CS.vEgo
         actual_curvature = interp(CS.vEgo, [2.0, 5.0], [actual_curvature_vm, actual_curvature_llk])
       desired_lateral_accel = desired_curvature * CS.vEgo ** 2
+
+      # desired rate is the desired rate of change in the setpoint, not the absolute desired curvature
       desired_lateral_jerk = desired_curvature_rate * CS.vEgo ** 2
       actual_lateral_accel = actual_curvature * CS.vEgo ** 2
 

selfdrive/controls/lib/lateral_planner.py

@@ -79,6 +79,9 @@ def update(self, sm):
                      y_pts,
                      heading_pts)
     # init state for next
+    # mpc.u_sol is the desired curvature rate given x0 curv state. 
+    # with x0[3] = measured_curvature, this would be the actual desired rate.
+    # instead, interpolate x_sol so that x0[3] is the desired curvature for lat_control.
     self.x0[3] = interp(DT_MDL, self.t_idxs[:LAT_MPC_N + 1], self.lat_mpc.x_sol[:, 3])
 
     #  Check for infeasible MPC solution