Sending position data using MAVSDK mocap

I am trying to use MAVSDK-python mocap plugin to send “position” data relative to an external vision system to the drone. The goal is to obtain position lock without GPS receiver onboard. My external source would not have any other information about the drone besides position (i.e. no attitude information).

I noticed VisionPositionEstimate() function requires angle_body and pose_covariance parameters in addition to position_body.
I am not sure if I fully understand these parameters and how to calculate them. Is there a way to use this function ( and mocap plug-in of mavsdk in general) to only send the position of the drone?