COEX Clover 4.2 Control Law Design

Hello Community, i’m currently developing a project where im coding the control law, the quadcopter im using is a coex clover 4.2 with a pix card, my doubts are related to the way i can get the position of the drone?, what codes should I check o what can I do to obtain the position, using the different positional sensors with a topic from ROS?, thank you in advance