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Comparing Tractor GPS with Rod GPS

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April 04, 2017 09:58AM
Hello all - I'm new to the forums here and relatively new to FMX software. I work as a surveyor and GIS specialist with my local Department of Agriculture where we do soil conservation design to assist farmers with erosion issues. Our Soil conservation structures (terraces, berms, waterways, etc.) need to account for farmers' AB lines in the field.

We've been working with a local farmer to compare some GNSS system outputs (tractor and on the ground)

I was in the field yesterday with a farmer and he surveyed a few lines with his GPS (cm accuracy) unit on his tractor. I followed along and placed flags directly in the center of his hitch, then measured them with our own Trimble GPS unit with cm accuracy connected to a local VRS network.

I downloaded the Swath.shp files from the survey and loaded them in ArcGIS along with the points file that I collected in the field. I converted my points to lines (as seen on the attached map). Both surveys used the same datum

I've attached a map here and You can clearly see that the Swath line from the tractor does not line up with the line I measured with the Rod. The first line (to the west) is off by about 15 feet. The second line is off by about 35 feet and the third line is off about 33 feet.

The extents of the line to the North and South are not of concern. The red dots shown on the map were part of the file I downloaded from the Tractor GPS which is a log file (3DTrack file) showing where the GPS was measuring the tractor's location as it was running the survey. These points line up well with the line that I measured in the field - which means there must be an offset applied to the Swath line that the farmer picked up.

I'm not very familiar with FMX or the Tractor GPS gear but I'm sure it's a setting that needs to be changed here?

Any help is appreciated - Thank you in advance


Map of field test


Comparing Tractor GPS with Rod GPS

eymacdonaldApril 04, 2017 09:58AM

Re: Comparing Tractor GPS with Rod GPS

Scott NusbaumApril 04, 2017 04:55PM

Re: Comparing Tractor GPS with Rod GPS

eymacdonaldApril 05, 2017 10:46AM

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