This question already has an answer here:
Even when the Falcon 9 "punched the barge", it did so with extreme precision. SpaceX has now had several successful landings, many of them extremely spot-on. Two questions:
There are obvious visual navigation markers on the barges. Is that only for show, or does the Falcon 9 use visual navigation?
What other techniques (if any) does the Falcon 9 use to enable those precision landings?
To be specific, I'm asking about terminal guidance. GPS alone will not do the trick. Relative GPS might do the trick.