External GPS Ardusub / Mavlink / Mavros

Hello,
I have been working on starting up a new underwater project that will be using Ardusub. I’ve used it before, but never quite like this.

Typically, I’ve just used it in manual mode with a controller connected and I’ve been sending rc overrides through a mavlink/mavros connection to my sub and controlled it that way. Now, however, I want to include some of the nice autonomy features that Ardusub can do.

At the end of the day, I want to be able to select waypoints in QGroundControl then send them to the sub to follow autonomously. For my sub, I do some SLAM localization and get a starting GPS location, so I have what is essential a GPS sensor on board that can spit out GPS lat/lon. I want to feed this into Ardusub so it can use this information to do the waypoint navigation, preferable using mavros to send this gps data.

So, my questions are:

  1. How do I send Ardusub a GPS location that I know the sub is at?
  2. Once I’ve given it a GPS location, how do I tell it to start following these waypoints?

Any insight into this would be super helpful!
Thanks!