GPS receiver data


I am involved in a project at my university where I have to develop the flight code for a Pixhawk 4-powered quadcopter which is running PX4 autopilot version 1.8. I am programming the flight control system with the PX4 Embedded Coder Support package for Matlab and I have two questions.

Firstly, for this task, I need to extract the data of the current velocity of the UAV from the GPS sensor. I tried to read the information by importing the data from the vehicle-gps-position MSG file, but the MSG file does not give any data at all. I have also tested the GPS receiver by installing the PX4 Flight Stack v1.10.1 Stable Release setup with QGroundControl and the GPS-function worked. Which of the MSG files under Firmware\msg do I have to use to obtain the position and velocity?

My second question regards the Extended Kalman Filter (EKF). Is it possible to obtain the velocity in body-axis coordinates from the EKF. If yes, where do I find it in the Firmware?

Thank you!