GPS acre counter vs GPS

When using a GPS system in planting corn or beans, which do you go by, the one on the planter, or the acre numbers from the county FSA. I have a dispute with the custom planter guy about how many acres are in the field, he wants to go by his GPS system on his planter and I want to go by what the county office says..how can there be any difference in the acres if the GPS is run off of the same satilite??? I dont know how to spell sateilitey..

I'd be inclined to go with the county FSA figures, and put the onus on him to prove otherwise.

I assume the FSA figures are in your favor.

The question should be why don't the GPS systems record the same figure? Thanks

I think the fsa is now using aerial maps and then tracing them out by computer. They used to have this device that traced out the perimeter and transfered it to scale to calculate the acres.

Is your ground flat or hilly? The aerial view of a hillside or even a mountain side just shows a slice from over head. But if you were to measure off the surface area, it would be more.

The FSA does not use GPS. They trace aerial photographs. You can do this yourself on the website for NRCS soil maps. As others have mentioned, a hilly site will show less area from an aerial photo than will an accurate GPS measurement.

This isn't a huge effect -- for a field with a steady 10% grade the aerial photo method will give 99.5 percent of the true area measured along the slope of the hill.

Non-differential GPS, even with WAAS, is not accurate enough to measure field area or distance of travel with 0.5 percent of precision. You need a separate, local transmitter to begin to approach that accuracy, AND the operator has to set up the equipment and use it correctly.

One example way to mis-use the equipment would be to use the GPS to measure distance traveled, then multiply by swath width to come up with "area". Naturally, this will over-estimate area by the amount that any swaths overlap each other.

I would query the operator closely as to exactly HOW the gps calculates area, when the equipment was last calibrated, and what comparisons he's made against between reported area surveyed area. If the answer is "I push the button and it give me the area, I don't know how it does it, I've never tested it", then I'd be unlikely to accept his numbers unless the difference was too small to argue about.

I used a handheld GPS on my 4 wheeler and drove around the perimeter of all my fields. It read out acres to three decimal points. I'd say the GPS on the planter is pretty much balls on, and up to date.

Gordo

Our county has the maps on computer and they use a computer program now. They click dots around a field and the pooter conects them and figures the area. It is quick and most of the time close but they ain't always right. I know I have some real small fields that FSA says are twice as big as they really are. I'd put money on the planter if I was gonna bet which was closer.

Dave

Red, I just had some ground grid sampled by GPS. The operator rides around the perimeter of the field and the field is measured to start with. This is about as accurate as you can get. Several of my fields have different measurements than FSA have on the same thing. So don't think that FSA's figures are absolute because they are not. I have done a lot of custom work for others and when you include point rows, etc., it is not unusual to have more acres on a machine than what FSA calls for. I tell everyone before I start that I will get paid for what is on the drill/planter, etc., whether it is in my favor or against me. You would be surprised how many times there are LESS acres than someone thinks there are. Unless the figures for your custom operator are way off, you'd better pay him and be happy you have a good operator to do your work. Many don't care for anything but to cover acres. Mike

I have checked all three, the google planimeter, the FSA and handheld GPS. They were all pretty close to one another.
Google Planimeter

Well, Google Planimeter doesn't seem complicated enough to mess up, BUT.....I just ran 3 recently surveyed plots of 12, 20, and 56 acres and Google told me each was about half size or smaller?????????????? :roll: