Perhaps relevant to this subject, there are now <$400 three-band GNSS compass receivers (e.g. two three band receivers in a single unit so you can run two antennas with a meter or two baseline and get accurate headings in addition to position), based on the Unicorecomm UM982 chipset. E.g. https://www.ardusimple.com/product/simplertk3b-compass/ (There are other vendors, but I've done business with this one before)

I mention it because for imaging, small heading errors have way more impact on where you're looking than small position errors but single antenna gps doesn't really give you headings except with assumptions from motion.

I've got one sitting in a box here, haven't tried it out yet but plan to soon...