I believe "ground zero" is the first point where you use the Homelink. In my case it is where the home link is trained to the opener (when I push the opener button to recognize the Tesla Homelink).
On the Tesla screen touch the Homelink icon, (green house), at the bottom touch "Homelink Settings", in the next screen touch "garage" (your name may be different). Enter the distance, from ground zero, you want the door to open, check the box "Auto-open when arriving". Close all screens and drive away, I'm not sure how far but the car has to know you left and are coming back. I have gone around the block and it satisfied the requirement.
It should work.
NOTE, you can't program two things to trigger at the same time, like a gate and garage. The Homelink transmits for 5 seconds so you will have to stagger the distance so they don't go together or only one will open.