Folks,
Haldir is correct. The EXACT location of the vision tetras is indeed a "known" position and is accurate to one inch. The official field layout is
HERE.
I also created a larg-scale paper "tabletop" playing field
HERE as well as a printable 11'x17" playing field with no dimension lines
HERE which does indeed show the floor markings of where the randomly-placed vision tetras can possible go.
The referees will place the vision tetras onto the field on the pre-difined spaces at the beginning of a match "very shortly" before autonomous period starts.
So....You could pre-program your robot to "know" all eight possible locations and send a signal just before the match that the vision tetras are in locations #2 and #7 as an example. Or........read on
There is a separate discussion about enabling the on-board cameras to watch the field and to seek-out the location of the vision tetras as they are being placed, even before the gun goes off....very advanced....and scary!