# Covariance matrix for /vo and /odom

Hello there! I am currently trying to fuse the odometry messages from the ROSARIA and visual odometry messages from viso2_ros libraries using the robot_pose_ekf. However, I seem to always encounter an error of where the covariance matrix is zero.

I am still a beginner, and I have read a little about covariance. I would like to know how to implement the covariance or include some appropriate values into the matrix in order for the robot_pose_ekf to work succesfully..