I have a project, it was started by another firm and it is part of an older ROS of my company. We have four ROS in the same section from the early 2000's to 2023. The 2023 survey is based on DOT control given to us with a mix of old DOT monuments and new. The old ones have shifted from earlier lat, long locations by about .1'N, .1'E., more or less and DOT resurveyed them with new coordinates. We scrapped old coordinates and relocated everything needed for that one project which starts at the new subdivision and heads south only touching the new subdivision along the south like. We saw a fairly consistent .15-.20' shift, not exact but at least moving the same direction all the time. All our ROS's used the community factor of 1.000235 as did the two DOT projects. DOT multiplied grid coordinates by the scale factor, so we continued with that system.
The new project from the different firm calculated a scale factor by using a coordinate, jumping up and down on it, slapping it in the face, throwing it into a Least Squares program and coming up with 1.00023549. So I plotted the figures sent to me and found it didn't fit the other coordinates by about 600' or the shift from grid to surface by multiplying coordinates. Clearly, they expanded around a point, somewhere. But metadata from them didn't say where. I had two really good candidates, and since I couldn't get with the surveyors who were off on an out of state project and the engineer didn't know, I tried both and sure enough the one which is a concrete and capped DOT control point just west of the site was it. Using it everything fits by applying the scale factor to the distances from it. Then in a fit of inspiration I calculated a scale factor for that point-1.00023549. They set on the control point, punched a button and it kicked out that factor and away they went. Not a big deal, but metadata is a must. I had to do a plat for the subdivision and I included the control point, lat's and long's on it and some section corner ties and the scale factor showing the control point as the scale point, should help the next guy.
But now I have to expand a survey using the new subdivision system. I have old coordinates on points, I can simply download the lat, long from them into the new, but there is that shift. It's really annoying. We do know that over time the ground will shift at many of our sites, the earth isn't stable, coordinates drift, the world is ruled by physics and that will never change.
The longer I do this the more I'm convinced that the idea of a coordinate system for boundaries is a terrible idea. We will see today if my calcs fit the section corners and by how much they are "off".
The longer I do this the more I'm convinced that the idea of a coordinate system for boundaries is a terrible idea. We will see today if my calcs fit the section corners and by how much they are "off".
AMEN
AMEN
DOT multiplied grid coordinates by the scale factor, so we continued with that system.
That is not correct in my area because GRID = GROUND x CSF on our maps. So GROUND = GRID / CSF.
DOT multiplied grid coordinates by the scale factor, so we continued with that system.
That is not correct in my area because GRID = GROUND x CSF on our maps. So GROUND = GRID / CSF.
Yes, they multiply grid coordinates by the project scale factor to produce surface coordinates. These of course aren't calculated for each point, a project scale factor is to simulate a surface close to ground. It would be possible to calculate each point's grid scale and height scale then recalculate a surface coordinate, but that would add an enormous amount of work for all concerned.
They have been doing it this way since at least the 1960's so almost 60 years now that I know of.
Trimble's local site setting also does it this way, for Autocad you need to imput the inverse so 1.000235 becomes .999765,,,,,. Both work.
Their data sheets explain the process.
To an outside observer, many of the DOT procedures seem mired in the past, archaic and just plain weird.
Trimble's local site setting also does it this way, for Autocad you need to imput the inverse so 1.000235 becomes .999765,,,,,. Both work.
Their data sheets explain the process.
That's what we do on every project and ALWAYS scale to 0,0. With those two things set in stone along with a master spreadsheet to document each project metadata that all staff use and include on all our plans makes jumping into any project simple. No funky rotation, no scaling to a central point no one knows about.
That's what we do on every project and ALWAYS scale to 0,0. With those two things set in stone along with a master spreadsheet to document each project metadata that all staff use and include on all our plans makes jumping into any project simple. No funky rotation, no scaling to a central point no one knows about.
A long time ago we would pick a NGS monument to fix with state plane then create a scale factor between it and the nearest NGS monument that would corral our project. Then we would calculate a new coordinate for the second NGS monument applying the scale factor to the inversed grid distance, then survey from the fixed point to the new coordinates for monument #2 using strictly ground distances. With GPS that isn't such a big deal. But running traverses with a T2 and distance meters it made for a good way to get coordinates without reducing everything to grid for each calc.
I objected to the DOT system cause I couldn't plot coordinates on a quad or photos, of course once those became easily available electronically, that objection became moot.
Three words: .... Low ... Distortion.... Projection.
Here for our DOT they have a similar method. Scale factor x’ coordinates to get to ground yet they do set up a false northing and easting historically. For everything not DOT a bunch of different methods are used. Some scale from a point a known one or centroid of project. Most do not provide the metadata though. Some do about 0,0 still no metadata usually. No scale no lat long or origin you can usually tell fairly quickly if it was about 0,0. I personally hate the scaling but it’s what is done so I do it. When I do I make sure I provide the lat long ellipsoid height used the combined factor and the reciprocal of that. We do place that on the plats in a note. So anyone following us should be able to quickly compile in state plane or at the surface and be pretty darn close to everything we did within our measurements capabilities and such. Doesn’t mean they should use the coordinates for the boundary just an extra tool to get them close to finding the same evidence we platted. There are some changes coming to our regulation that I believe will aid in folks providing the metadata hopefully.
I do see the absolute tremendous advantage of using a LDP but it’s just not practiced here.
Perfection is a myth, especially when it comes to coordinates.
Today, I was reviewing a survey that took a 20-sided new tract being subtracted from a tract surveyed three years ago which is adjacent to a tract created four years ago. The current survey required one new monument be set something like 11.00 feet from a monument common to both prior surveys. The bearing of the 11.00 foot piece differed by close to five arc-minutes or very close to 0.015 feet from the line it was supposed to occupy.. Every other monument on the combination of three surveys were exactly where they were put. I know what happened. They set the new bar, then reshot it to find it was "off" the old line by that amount. One whack on the bar would have fixed things. We know the "finding" all of the old monuments in perfect locations to be only in someone's imagination.
Perfection is a myth, especially when it comes to coordinates.
PC located the E1/4, the N1/16 on the east Section, and the CN1/16. The E1/4 was .02' from the calculated position using new tweaked 2011 coordinates, the CN1/16 was .01' but the N1/16 was .11'. He shot it multiple times but kept coming up with the same result. Still, what am I doing even wondering about it? Time to touch grass and move on.
@mightymoe so true. If it was more I I probably would have moved along myself. Good grief I mean the math will lead you to the monument I am not getting upset over a small discrepancy in a darn measurement. I get excited that I land on the bar or pipe or stone etc.
@mightymoe so true. If it was more I I probably would have moved along myself. Good grief I mean the math will lead you to the monument I am not getting upset over a small discrepancy in a darn measurement. I get excited that I land on the bar or pipe or stone etc.
GPS is changing my expectations. We keep returning to old monuments and seeing 1cm or less. We check DOT control and see 1/2cm or less. We are also finding moving monuments. Some are hills sliding some are messed with. Of course, 0.11' isn't much of evidence of either.
@mightymoe In 2018 we had a strong earthquake, 7.8 I think. Some areas I had surveyed in shifted up to a 1' while others didn't move at all less than a mile away. I suspect that there were some areas that I never got back to where the shifts were a good deal more substantial seeing what happened to some building's foundations and roads split apart. I look at all measurements on monuments as just a snapshot in time.
Just because I'm paranoid, doesn't mean they aren't out to get me.
@mightymoe In 2018 we had a strong earthquake, 7.8 I think. Some areas I had surveyed in shifted up to a 1' while others didn't move at all less than a mile away. I suspect that there were some areas that I never got back to where the shifts were a good deal more substantial seeing what happened to some building's foundations and roads split apart. I look at all measurements on monuments as just a snapshot in time.
There is a township corner. In 1979 I went with a helper and set a brass cap for it. Then in the mid 1990's we had a boundary and located it again. It didn't seem to fit very well to the 1979 position but I didn't think much about it. Then in 2000 with GPS we located it a third time and it didn't fit either old location. Then a new job around 2010 and there was a foot of movement from 2000, same thing in 2020, just about 1' each time moving SE. Plotting all the movements from 1979 and it's really close to 1' per decade southeast. Where it was in 1880, there isn't any way to know. But it would makes sense that it was 10 northwest of the 1979 position and 14' northwest of the 2020 position. The cap looks totally undisturbed, standing plumb and a foot or so above ground.
@mightymoe I've seen some BLM monuments on slopes, with the freeze thaw, just gradually moving down the mountain at a glacial pace, but they usually have a good lean in the direction of travel. What are you going to do. Makes for an ambulatory boundary I guess. Did this one survey some years back on a piece of property a family was fighting over after their homesteader father passed. They all wanted this piece of bluff to build their dream home. Long story short, since the property was originally surveyed by BLM in 1950, the bluff had eroded back I estimated at a rate of a foot a year to where all that was left was a dining room table size portion. When I broke the news to them the parcel they'd been squabbling over for a decade no longer existed, the fireworks were spectacular and I was berated to no end, to which I responded to them as calmly as I could muster. 'Look, I just measure land, I don't make it and I don't take it away. You'll have to take this up with a higher power than me.' Later they asked if I'd do more work for them. I told them I'm too busy. Left out the part, 'not for all the tea in China'.
Just because I'm paranoid, doesn't mean they aren't out to get me.
@mightymoe so true. If it was more I I probably would have moved along myself. Good grief I mean the math will lead you to the monument I am not getting upset over a small discrepancy in a darn measurement. I get excited that I land on the bar or pipe or stone etc.
GPS is changing my expectations. We keep returning to old monuments and seeing 1cm or less. We check DOT control and see 1/2cm or less. We are also finding moving monuments. Some are hills sliding some are messed with. Of course, 0.11' isn't much of evidence of either.
I adjusted a rtk network some terrestrial observations from a job that the subject parcels were last surveyed in 1939 and 1958 for the ROW. Anyway all in canopy except a few corners. A tough survey. After getting the research all done and except a few outliers I had to get crew to get additional observations on it all worked very well and alll called for distances and bearings of subject and abutting properties the LS had the research on said man this all works great. I went last week and located 26 monuments ran through them all twice base at 2 different locations a 1945 survey. All RTK base and rover great results. Now to send a crew up to do the Topo work. With a little patience and redundancy GNSS has come a long way for sure.