Scale Factor
Any attempts to use micrometers to reconcile work done first by axes and later by cross-cut saws will be mindwarpingly futile.
It is more vital to conquer the sloppiness that exists today. A section corner and the section's east quarter corner were monumented as being 2579.86 feet from each other many years ago. Section corner references reports were filed with the State and the County for those corners. Surveys were made for small tracts on either side of the section line they formed. Those surveys were on file with the County. A highway improvement project comes along straddling that line in 2020. The new monuments, in monument boxes, are now 2577 61 feet apart. It makes one wonder what happened every half mile over a 15 mile project.
Could the old monuments not be found. Why did they set new monuments.
A section many years ago we were retracing for ROW survey had a nice big disc all stamped and the RM’s all done easy to find nice well drawn monuments record. We we eating lunch a few of us had gathered and had completed a weeks worth of static surveys. As always in my younger days I was curious and always practicing setting up the instrument to become better and faster than the next guy during lunch. I bucked in on a fence line to see how it lined up with the monument. It did so nicely. As I walked around in awe of the beautiful landscape in Colorado being from Mississippi I noticed a nice hedge row of those tumble weds in the distance. I wiggled in on it and spun the bearing around to the monument and I was missing it so kept trying I walked down a hill and found a small patch of cotton wood trees and remembered some of the old notes and started peaking around. That grove was about 50’ ft off the line of the new fence line but the pristine was found that day and the reference stone beneath that. A little wiggling in and looking at how the old fence line caught all those tumble weeds like a net proved to have been built on that line. A nice subdivision was tied to the new mark not the original. All luck I found it but it was neat and the distance matched they had just drifted over the course. I use to love reading the GLO notes and such.
Learning the underlying math is relatively easy when one has a lot of free time, but applying this stuff in the field under time and terrain pressures is a whole different matter. Using abstract mathematical inventions like ellipsoids and the planes that approximate them to produce usable and valuable surveys is the enviable skill.
When I was in school in an engineering class road and bridges. The professor made a statement to us students. He was trying his best to attract more of us to the civil engineering side of the house.
Yall can do this in here out of the weather as engineers or you can become surveyors and do it on the hood of a truck in all weather and fighting mosquitoes ticks snakes and who knows what else and make less money. Your choice.
Well I joined the United States Marines because it was a challenge and I followed the surveying route. I reckon I will never learn LOL. I guess he motivated me in the other direction. Or just stubborn pride to do something that most would not even try.
There are many ways to "get on ground". When we first got GPS we calibrated to terrestrial control. That didn't last long as it tends to degrade the accuracy of the GPS putting it down to the level of the total station.
Then we started using LDP's for areas, which I prefer to do, since I can get near to ground, and my grid bearings are closer to "true".
A township survey with the CM of a TM projection near the center of the township will rotate about 2 minutes along the east west edges. For most townships that's well within the original survey's accuracy.
But the advantage with the DOT method is that you can easily import-export data into your programs. All you need to do is have the one scale factor and much of online data will sample in without any manipulation.
"But the advantage with the DOT method is that you can easily import-export data into your programs. All you need to do is have the one scale factor and much of online data will sample in without any manipulation."
Absolutely true and that is sufficient justification for using ground coordinates, given that distance calculations produce the same result regardless.
Here is a link to NGS Publication 5 where, on page 50, more insight to the site-wide combined factor is given: ManualNOSNGS5.pdf (noaa.gov) It will go to your search engine rather than to the site where navigation is pretty straight forward.
It's also helpful to read beginning on page 46. The discussion is centered on converting ground observations to state plane, but it's just the other side of converting state plane to ground.
Of course, reading the whole manual with pencil and paper in hand can be a very productive use of time.
Which is is why I will never get licensed! 😚
