First and foremost, I'm a robotic total station user and not up to speed with GPS as many of you are, so here's my question:
I serve on a local board with a member that is a very large cash cropper. He was talking about demo'ing a new precision ag system (GPS for tractors). The salesman told him to expect half-inch accuracy. This is the second time in the last two weeks I heard this statement. My son is considering going to school for agricultural engineering and during a college visit the professor was claiming the same thing.
Is this possible?
Tractor salesman/used car salesman, what's the difference.......No!
Surveying with a tractor. Great concept!!! No more brushing!!! Just mow everything down. And... you can plant crops at the same time. Its a win-win all the way around.
I too have heard the same thing from my dairy farm clients. I highly doubt it, but do know that Cat/Deere maintain their own reference stations which are accessible by subscription only. Wonder if the data can be accessed to supplement the local cors?
Sure and they can measure the elevation changes of the oceans to 1mm. 😛
But my experience with machine control is in mines and it isn't within 1/2 inch.
But what in a field needs to be done to 1/2 inch?
The thing about GPS is that it can surprise you just how good it can get then surprise you just how bad it can be.
I have long noted an increase in accuracy after the rover has settled in for ten seconds or so. I suspect the unit may be that accurate if the tractor is sitting, but not if moving.
They're stating half-inch "accuracy" as though it's a constant. Your verticals can be expected to have twice the uncertainty of the horizontals. If what they were saying is true, expect 0.5" horizontal positioning and 1" vertical.
The statements they make are also based on ideal satellite geometry, no multipath, and (probably) averaging a parked vehicle. When in motion it likely uses the same stakeout routines that our RTK systems do, in which case it's using an old correction from the base to establish a position. Since the equipment is being operated by people without the technical knowledge of what's happening, I would bank on no better than 1-2" horizontal and 3" vertical precision to account for the many potential issues.
I'd tell them they better investigate a little further - like everything else - show me the mfg. specs.
However, 1/2 inch vs 2 inches horiz and 1 inch vs 4 inches vertical for precision farming - they'd never know or find the difference in the field.
I had to remind one of my clients that uses RTK for farming that using it for surveying is like buying dentist's tools and performing a root canal at home on his wife.
We have a number of Precision Ag subscribers to our C4GNet service here at LSU. The farmers seem to be happy; don't know what accuracy they're getting, though. They do a lot of work 24/7, just like the offshore geophysical surveyors.
I would be surprised if precision AG positioning was interested much in vertical accuracy. But they are using the same signals if they doing network or base/rover RTK positioning, no reason it should be any worse than a survey-grade unit in land surveying applications.
One possible difference is that except for the times they are working along the edge of a field that has a stand of large trees, most of the time they are in near ideal GPS conditions with clear sight lines horizon to horizon.
Half-inch accuracy relative to......what? Do they know where their fences are to the nearest ½"...no. Do they know where their edge of their field is to the nearest ½"? - no. Do they know how and where the wheels and/or tools on their tractor is in relation to the antenna to the nearest ½"? - no. Is it ½" global accuracy? Probably not, and they don't need to know that either. What do they have? Maybe, on a real good day, some of their data is accurate on their antenna in relation to the base station whatever the network is using.
Do they need ½" accuracy? No, they are driving a big tractor on terrain that they don't necessarily even know the ground elevation that well.
Where's the harm? The disservice, I think, is to surveyors when the consumers seem to think they probably can survey in property corners to ½" accuracy. They don't realize the surveyor's needs for control and that we need to survey in controlling monuments and determine the local property pin's locations based on field data. They think that the GIS down at the county has some kind of perfect coordinates that, if they can get to them within a ½" they will know where their properties are.
Some of the systems have gone to RTK. So 1/2 inch is sort of stretching the truth but it should be about as good as we get if they do everything right.
What I'd like to be able to do is buy the same equipment for about 1/2 the cost.
They could get corrections from a network same as us (some do). I think the AG GPS equipment market dwarf's the survey market.
Some planting systems plant between the last years rows. Say small grain on a 6 in row spacing and you want to be in the middle of last years rows in a no till situation. You's want to be fairly tight.
> I would be surprised if precision AG positioning was interested much in vertical accuracy. But they are using the same signals if they doing network or base/rover RTK positioning, no reason it should be any worse than a survey-grade unit in land surveying applications.
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> One possible difference is that except for the times they are working along the edge of a field that has a stand of large trees, most of the time they are in near ideal GPS conditions with clear sight lines horizon to horizon.
Not true. Move your rover around while trying to get a shot and see what it tells you.
Ultimately, a half of a foot for moving navigation should be obtainable, which for EVERYTHING I've EVER done on a farm or with a tractor (save mowing where I shouldn't have been) is MORE than accurate enough.
Machine control has come a long way.
Some big farms in Louisiana are close to having as many RTN subscriptions from us as big Surveying/Engineering firms. Plus, the (on land) surveyors don't work 24/7 in some seasons like the farmers will do. We deal with the equipment dealers rather than directly with the farmers because oftentimes it takes a lot of hand-holding when a farmer is getting started. We are better suited to working with Land Surveyors.
>Case IH AFS® equipment can achieve sub-inch (2.5 cm) accuracy, repeatable 95 percent of the time.
Sub inch sounds reasonable since I assume they are using survey grade RTK. I believe the stats for RTK accuracy are typically expressed as 1cm 68% of the time, 2cm 95% of the time, and 3 cm 99% of the time. So, if they are saying 2cm (sub inch), 95% of the time, it sounds reasonable to me.
Some of the systems also have tilt correction capabilities since the antennas are usually mounted on top of the combine or tractor cab. I use my Trimble RTK surveying equipment with the rover mounted on the front of the tractor hood. I don't use auto steer, just a light bar, but I can split 30" rows of corn stalks with 2-15" bean rows and stay off the rows without much effort. Auto steer would make it effortless, I'd probably go to sleep. 1/2", nope, 1", yep.
I was talking to my cousin in the panhandle last year, they were using RTK. I don't think their equipment is the least bit concerned with elevation, just location.
Some areas are putting in underground irrigation systems and want the rows planted on top of the irrigation tubes to maximize the use of water.
It's come a long way since I was a kid on a cotton farm.
The oddest thing I have seen recently is when they started round baling cotton.
James
My wife has some friends that run in big time farming circles in the Columbia River valley (pun intended of you know the area). I keep having this nagging idea that a consulting business that combines setting up and supporting the hardware & software with mapping and GIS could be a very interesting endeavor.