Set value for distortion coefficient in CameraInfo

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Hi,

I am currently working with 2 stereo cameras and I wish to publish their information on ROS topics (sensor_msgs/Image and sensor_msgs/CameraInfo ) for using the stereo_img_proc package.

I can publish my stereo camera images the sensor_msgs/Image but I am missing one component for the other one, ie sensors_msgs::CameraInfo message/object.

From the online documentation for CameraInfo.msg message, the distortion array D is declared as

float64[] D;

My current attempt does this -

      sensor_msgs::CameraInfo caminfo; 
       cv::FileStorage fs; // using OpenCV to read YAML file 

// read parameters as openCV cv::Mat and then fill array
       cv::Mat D1;
       fs["distortion_coefficients"] >> D1;
       caminfo.D[0] = D1.at<double>(0,0);
       caminfo.D[1] = D1.at<double>(0,1);
       caminfo.D[2]= D1.at<double>(0,2);
       caminfo.D[3] = D1.at<double>(0,3);
       caminfo.D[4] =D1.at<double>(0,4);

However, this does not work and I get an error ( Segmentation Fault core dumped ) on running the node/executable. This is probably because I'm making assumptions on the distortion array length but in reality I'm not aware of where the length is defined , since it is not given even here,

My Question: Can someone please explain how to fill in the distortion matrix parameter for sensor_msgs::CameraInfo ?