diff --git a/README.md b/README.md
index 0b97702..af28b22 100755
--- a/README.md
+++ b/README.md
@@ -1,3 +1,8 @@
+# What I changed (longfish) #
+In file include/plugin_drone.h, changed from ignition/math4/ignition/math.hh to ignition/math6/ignition/math.hh, as we installed the Ignition Citadel which is compatible with ROS Noetic.
+
+Added the /ground truth/state plugin in sjtu_drone.urdf model.
+
 # About sjtu_drone #
 
 sjtu_drone is a quadrotor simulation program forked from ['tum_simulator'] (http://wiki.ros.org/tum_simulator) , which is developed with ROS + Gazebo. It is used for testing visual SLAM algorithms aiding with different sensors, such as IMU, sonar range finder and laser range finder. Here by 'sjtu', it means Shanghai Jiao Tong University. Currently, this program is used for testing algorithms for [UAV contest in SJTU](http://mediasoc.sjtu.edu.cn/wordpress)
@@ -40,4 +45,4 @@ forward looking camera :  /drone/front_camera/image_raw
 downward looking camera: /drone/down_camera/image_raw
 sonar data:  /drone/sonar
 laser range data: /drone/laser
-```
\ No newline at end of file
+```
diff --git a/include/plugin_drone.h b/include/plugin_drone.h
index 874a902..cb524bc 100755
--- a/include/plugin_drone.h
+++ b/include/plugin_drone.h
@@ -4,7 +4,7 @@
 #include "gazebo/gazebo.hh"
 #include "gazebo/physics/physics.hh"
 #include "gazebo/common/Events.hh"
-#include "ignition/math4/ignition/math.hh"
+#include "ignition/math6/ignition/math.hh"
 #include <ros/callback_queue.h>
 #include <ros/ros.h>