How to subscribe to Array message

edit

I'm writing a program that subscribes to the topic "color / yolov4_Spatial_detections", gets the xyz coordinate value from "geometry_msgs / Point position", gets it with MOVEIT, and does pick and place work.

For now, I'm creating a simple node that subscribes to xyz from "yolov4_Spatial_detections".

I don't know in detail how to subscribe to a message file with an Array structure, and the following error occurs and the subscribe node goes down.

I have confirmed that [color / yolov4_Spatial_detections] is published in the rostopic list. I also checked the xyz coordinate information with a rostopic echo.

Can you give me some advice on how to subscribe to message files with this structure?

Thank you

#include <ros/ros.h>
#include "geometry_msgs/Point.h"
#include <depthai_ros_msgs/SpatialDetection.h>
#include <depthai_ros_msgs/SpatialDetectionArray.h>


//void clbk(const depthai_ros_msgs::SpatialDetection::ConstPtr& msg) {
void clbk(const depthai_ros_msgs::SpatialDetectionArray::ConstPtr& msg) {

ROS_INFO("position: x=%.2f, y=%.2f", msg->detections[0].position.x, msg->detections[0].position.y);

}

int main(int argc, char **argv)
{
  // ROS objects
  ros::init(argc, argv, "yolov4_subscriber_node");
  ros::NodeHandle n;
  ros::Subscriber sub = n.subscribe("/yolov4_publisher/color/yolov4_Spatial_detections", 1, clbk);

  ros::spin();

}

error

   process[yolov4_subscriber-1]: started with pid [8158]
    ================================================================================REQUIRED process [yolov4_subscriber-1] has died!
    process has died [pid 8158, exit code -11, cmd /home/yo4hi6o/oak_ws/devel/lib/depthai_examples/yolov4_subscriber_node __name:=yolov4_subscriber __log:=/home/yo4hi6o/.ros/log/37964ede-bd18-11ec-a47c-e094679e2019/yolov4_subscriber-1.log].
    log file: /home/yo4hi6o/.ros/log/37964ede-bd18-11ec-a47c-e094679e2019/yolov4_subscriber-1*.log
    Initiating shutdown!
    ================================================================================
    [yolov4_subscriber-1] killing on exit

depthai_ros_msgs/SpatialDetectionArray.msg

# A list of 2D detections, for a multi-object 2D detector along with 3D depth information.

std_msgs/Header header
# A list of the detected proposals. A multi-proposal detector might generate along with the 3D depth information
#   this list with many candidate detections generated from a single input.
SpatialDetection[] detections

## These messages are created as close as possible to the official vision_msgs(http://wiki.ros.org/vision_msgs)

depthai_ros_msgs/SpatialDetection,msg

# Class probabilities
vision_msgs/ObjectHypothesis[] results

# 2D bounding box surrounding the object.
vision_msgs/BoundingBox2D bbox

# Center of the detected object in meters 
geometry_msgs/Point position


# If true, this message contains object tracking information.
bool is_tracking

# ID used for consistency across multiple detection messages. This value will
# likely differ from the id field set in each individual ObjectHypothesis.
# If you set this field, be sure to also set is_tracking to True.
string tracking_id

rostopic echo /yolov4_publisher/color/yolov4_Spatial_detections

detections: 
  - 
    results: 
      - 
        id: 0
        score: 0.507520675659
    bbox: 
      center: 
        x: 238.0
        y: 242.0
        theta: 0.0
      size_x: 388.0
      size_y: 374.0
    position: 
      x: 0.0630802065134
      y: -0.0779226049781
      z: 1.63851070404
    is_tracking: False
    tracking_id: ''
---
header: 
  seq: 221
  stamp: 
    secs: 1650080057
    nsecs: 312681360
  frame_id: "oak_rgb_camera_optical_frame"