We have an issue where someone mistakenly uploaded Colorado State Plane (feet)coordinates into a Garmin eTrex 10 with the correct datum but position format degrees, minutes, seconds, instead of first converting to a format that Garmins can read.

How do I reconstruct which coordinates she actually visited in the field?

The points were a ballpark of about 150 m too far south from desired location, not the whopping 60 degrees off that you would expect it to be off if it read them as lat/long? As an example, the uploaded file had point X as 478739, 448129 in state plane feet, vs. the GPS displays its coordinates as 105°15'05.0", 40°29'02.1"N. I hope someone has some insight on how to figure out the actual coordinates for the waypoints the GPS actually took her to.

  • I think this question is just too confusing to answer. Break it down into step-by-step actions in detail and you'll likely get an answer. Oct 3, 2016 at 21:47
  • as you noticed, it appeared to correctly read the state plane coordinates. There could be two issues. 1) a datum problem, NAD27 versus NAD83; 2) US survey feet versus Int'l feet.
    – mkennedy
    Oct 12, 2016 at 12:21

1 Answer 1


I ended up going back out into the field to record the lat & long of where the GPS believed the points were located, and it was off by 218 m. Not sure exactly how the GPS unit came to put them there, but now I know where the points ended up, so good enough.

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