Copter: surf tracking, do-land use inav alt

Also CTUN logging of inav alt switched to get directly from inertial nav
lib instead of using current_loc.alt

ArduCopter/Attitude.pde

@@ -240,12 +240,13 @@ static float get_throttle_surface_tracking(int16_t target_rate, float current_al
     static uint32_t last_call_ms = 0;
     float distance_error;
     float velocity_correction;
+    float current_alt = inertial_nav.get_altitude();
 
     uint32_t now = millis();
 
     // reset target altitude if this controller has just been engaged
     if (now - last_call_ms > SONAR_TIMEOUT_MS) {
-        target_sonar_alt = sonar_alt + current_alt_target - current_loc.alt;
+        target_sonar_alt = sonar_alt + current_alt_target - current_alt;
     }
     last_call_ms = now;
 
@@ -259,7 +260,7 @@ static float get_throttle_surface_tracking(int16_t target_rate, float current_al
     target_sonar_alt = constrain_float(target_sonar_alt,sonar_alt-pos_control.get_leash_down_z(),sonar_alt+pos_control.get_leash_up_z());
 
     // calc desired velocity correction from target sonar alt vs actual sonar alt (remove the error already passed to Altitude controller to avoid oscillations)
-    distance_error = (target_sonar_alt - sonar_alt) - (current_alt_target - current_loc.alt);
+    distance_error = (target_sonar_alt - sonar_alt) - (current_alt_target - current_alt);
     velocity_correction = distance_error * g.sonar_gain;
     velocity_correction = constrain_float(velocity_correction, -THR_SURFACE_TRACKING_VELZ_MAX, THR_SURFACE_TRACKING_VELZ_MAX);
 

ArduCopter/Log.pde

@@ -315,7 +315,7 @@ static void Log_Write_Control_Tuning()
         angle_boost         : attitude_control.angle_boost(),
         throttle_out        : g.rc_3.servo_out,
         desired_alt         : pos_control.get_alt_target() / 100.0f,
-        inav_alt            : current_loc.alt / 100.0f,
+        inav_alt            : inertial_nav.get_altitude() / 100.0f,
         baro_alt            : baro_alt,
         desired_sonar_alt   : (int16_t)target_sonar_alt,
         sonar_alt           : sonar_alt,

ArduCopter/commands_logic.pde

@@ -345,7 +345,7 @@ static void do_land(const AP_Mission::Mission_Command& cmd)
 
         // calculate and set desired location above landing target
         Vector3f pos = pv_location_to_vector(cmd.content.location);
-        pos.z = current_loc.alt;
+        pos.z = inertial_nav.get_altitude();
         auto_wp_start(pos);
     }else{
         // set landing state