PX4 pos estimate integration into rtabmap-ros

Dear people.-

I want to use ZED-SDK camera with rtabmap-ros to build a global map. And, I wonder how difficult would be to integrate GPS readings from Pixhawk to a rtabmap-ros ?

2.-What I understand is that the PX4 computes an EKF which is a kind of SLAM, right? and this estimation is based on GPS, right?

3.-How about to integrate the estimation of the PX4 to the rtabmap to build up a map? do you think would be a good idea?

4.-The ZED camera contains already a odometry, and I am using that to build a 3D map, how about fusing that odometry with the estimation of PX4 and feed the rtabmap to build the map and later on fuse that map when using global planner?

cheers and looking forward for your replay?