Copter: precision landing velocity PI object

Follow up changes required to actually use this PI during landing

ArduCopter/Parameters.cpp

@@ -851,6 +851,28 @@ const AP_Param::Info Copter::var_info[] PROGMEM = {
     // @User: Standard
     GGROUP(p_pos_xy,                "POS_XY_", AC_P),
 
+#if PRECISION_LANDING == ENABLED
+     // @Param: PRECLNDVEL_P
+     // @DisplayName: Precision landing velocity controller P gain
+     // @Description: Precision landing velocity controller P gain
+     // @Range: 0.100 5.000
+     // @User: Advanced
+
+     // @Param: PRECLNDVEL_I
+     // @DisplayName: Precision landing velocity controller I gain
+     // @Description: Precision landing velocity controller I gain
+     // @Range: 0.100 5.000
+     // @User: Advanced
+
+     // @Param: PRECLNDVEL_IMAX
+     // @DisplayName: Precision landing velocity controller I gain maximum
+     // @Description: Precision landing velocity controller I gain maximum
+     // @Range: 0 1000
+     // @Units: cm/s
+     // @User: Standard
+     GGROUP(pi_precland,            "PLAND_", AC_PI_2D),
+#endif
+
     // variables not in the g class which contain EEPROM saved variables
 
 #if CAMERA == ENABLED

ArduCopter/Parameters.h

@@ -348,6 +348,7 @@ public:
         k_param_rtl_climb_min,
         k_param_rpm_sensor,
         k_param_autotune_min_d, // 251
+        k_param_pi_precland,    // 252
 
         // 254,255: reserved
     };
@@ -500,6 +501,10 @@ public:
     AC_P                    p_vel_z;
     AC_PID                  pid_accel_z;
 
+#if PRECISION_LANDING == ENABLED
+    AC_PI_2D                pi_precland;
+#endif
+
     AC_P                    p_pos_xy;
     AC_P                    p_stabilize_roll;
     AC_P                    p_stabilize_pitch;
@@ -570,6 +575,10 @@ public:
         p_vel_z                 (VEL_Z_P),
         pid_accel_z             (ACCEL_Z_P,       ACCEL_Z_I,        ACCEL_Z_D,      ACCEL_Z_IMAX,       ACCEL_Z_FILT_HZ,    MAIN_LOOP_SECONDS),
 
+#if PRECISION_LANDING == ENABLED
+        pi_precland             (PRECLAND_P,      PRECLAND_I,                       PRECLAND_IMAX,      VEL_XY_FILT_HZ,     PRECLAND_UPDATE_TIME),
+#endif
+
         // P controller	        initial P
         //----------------------------------------------------------------------
         p_pos_xy                (POS_XY_P),