I think that there are machines (possibly not road graders, though such
function would be useful) that work from either laser referencing or
differential GPS to put the blade under computer control, and ignore the
whole question of where the wheels are at or how long the wheelbase is,
just moving dirt to where it should be.

If you see any road construction near you these days, that's what that
globe on top of the 10' pipe attached to the dozer/grader/whatever
blade is for. I suspect they also use one when setting grade stakes,
etc. for use with excavators and such, too. I've noticed crews in my
area are certainly getting better road grades (more consistent slopes
and better drainage) with far less work-and-rework than even five
years ago.

But one of the weird side effects of all this technology is how much
of a piecework quilt things are starting to become, they used to have
to get everything to the same point (say the sub-grade) before they
went on to the next (say, the final grade before paving). Now you'll
get a 100' section graded and paved while they're still blasting and
digging and building retaining walls a few feet away, and it all lines
up perfectly with the next section already paved on the other side of
where they are still doing work. It's very interesting seeing
everything come together so well with as much change in the road base
they wouldn't even have thought possible in the same amount of time
not that long ago.

A lot of commercial farming is also done using a GPS, such as when
using a sprayer or broadcast spreader on a non-row crop where you want
to minimize gaps and overlaps (and thus over- or untreated spots)
without the reference points you get when dealing with produce grown
in rows.

--Glenn Lyford