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SF1 accuracy and lon/lat
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Posted 3/14/2023 14:26 (#10139757 - in reply to #10139527)
Subject: RE: SF1 accuracy and lon/lat

There are two aspects to GPS accuracy. There's the pass-to-pass accuracy (technically called precision), and then there's the accuracy of repeatably coming back to the same lat/lon position at a later time. If you make a pass with SF1 and turn and immediately make the next pass, the new pass should be within 4-6" relative to the previous pass. But if you come back in a few hours or days, it can be a foot or more off, requiring shifting the track to line up again. And over the course of a long day it will drift as well, relative to that first pass you put down. So if you mark a spot and come back in a month or a year, you'll be able to get maybe within a couple of feet of that original mark with SF1. For many farmers and operations, SF1 is quite adequate.

As for how much SF1 drifts, it depends on the receiver. With a Starfire 3000 I definitely get drift of about a foot over the course of a day. But like the previous poster said, it "comes back" around. In other words the drift is always +/- about an average. So it's not like your flags or boundaries are going to slowly march off the field.

Satellite-delivered systems like SF1, SF3, RTX, etc, cover a wider area, so they can never be quite as good as RTK because of variances in atmospheric conditions across that area, but advances in the math, and GPS receiver sensitivity allow SF3 and RTX to get near-RTK accuracy and repeatability. In practical terms, that might be an inch or less pass to pass, and a repeatability of less than 4" in my experience.

I use RTK mainly because I have my own base station that I built for cheap, and I have GPS receivers in my tractors that are already capable of working with it. I don't need the accuracy that RTK gives me necessarily, but the ability to come back and hit the line without any adjustments year on year is very nice to have, especially when working around pivots. And accurate boundaries to contain spraying is also very nice to have.

Edited by torriem 3/14/2023 14:29
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