I revisited a survey I did 20 years ago. Found a pair of my old control nails. They seemed to match fairly well. Couldn't find my gps base line due to road work. Started locating pins I set way back when. All had differences in location. 0.15' south and west. Some north and east. Had one on a ridge 0.50' down a ridge north and west, going toward a large pond. I could find the pins thou. This alarmed me. I'm very anal about surveying control and setting corners. This bothers me. I finished the day, and after getting home pondering the situation. This land is thick brown loam soil. I'm starting to think the soil is living, breathing, and growing causing the differences. I'm not sure what I'm going to do about this. Tomorrow I'm moving to the rear of the property to set up on an original gps point, and back sight a first traverse nail from it. I should see how they relate to each other.
Have any of you had this happen before?
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Being a West-coaster I consider seismic activity, 20 years is a long time.
YES!
Being able to find my hubs and other working points set decades ago is an important part of my normal day.
I have found similar movement and/or difference between what was noted?ÿ years ago with TS and what I find today.
With GPS, the difference is usually some ratio with how far apart the points are in relation to each other.
I do remember in the early to mid 80s that we began to include curvature of the earth as a setting in our TS and software before we had electronic data collection and carried that practice on to today. That has helped match GPS data of today.
No telling what has gone on with our hubs in 20+ years, I've found it common to observe possible movement of the ground and/or simple run over during a wet period and/or critter tampering and/or human tampering, etc.
We have many sandy loam and deep sand areas that 60d nails must be set deep to have a chance to stay in place.
It is necessary to practically set a deep post and place a 60d on top for some hubs locations.
All of the above.
In Northeast Mississippi, we have highly expansive clay in some parts. Some of our points "walk" around a bit.
Consider adding to the mix tectonic plate movement, which is noticeable in GPS work over time.
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