Apriltag pkg - Node crash when trying to get position

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Hello,

I'm trying to use a drone (iris model) with a camera in Gazebo to detect apriltag (AP). I cloned a usb-camera pkg, and the AP pkg. All works fine with the webcam. Now, I'm trying to use the position from the topic : /tag_detections_pose to get the position x,y,z. I'm coding in C++ with ROS Kinetic and use Gazebo 7.

I'm using the code provided (as base) by PX4 : https://dev.px4.io/en/ros/mavros_offboard.html

So I included the type of message: #include <geometry_msgs/PoseArray.h> // Tag detection Then, I create a global variable and a call back function:

   // Callback which will save the estimated local position of the Apriltag
   geometry_msgs::PoseArray APtag_est_pos; // Tag detection
   void APtag_est_pos_cb(const geometry_msgs::PoseArray::ConstPtr& AP_est_pos){
   APtag_est_pos = *AP_est_pos;
   ROS_INFO("CALLBACK AP");
   //    ROS_INFO("APtag est pos=[%f, %f, %f]",  AP_est_pos->poses[2].position.x,
   //                                            AP_est_pos->poses[2].position.y,
   //                                            AP_est_pos->poses[2].position.z);
   }

And finally I subscribe to the topic:

// The node subscribe to Topic "/tag_detections_pose", 10 msgs in buffer before deleting
ros::Subscriber APtag_est_pos_sub = nh.subscribe<geometry_msgs::PoseArray>
("tag_detections_pose", 10, APtag_est_pos_cb); // with or without the / ????

Like this it works, but if I try to uncomment the part that should give the position with ROS_INFO, I get this error :

[offb_node-5] process has died [pid 8044, exit code -11, cmd /home/mpperret/project_ws/devel/lib/waypoint_navigation/offb_node __name:=offb_node __log:=/home/mpperret/.ros/log/dbcc83d4-e8b8-11e8-acbf-54bf646662d7/offb_node-5.log].

Is someone know why ? Maybe I'm doing something wrong with the variable to get position x,y,z ?

Thanks in advance