Recently I've had two projects that were surveyed by out of state company's. One from Virginia the other from South Carolina. No big deal. We cover the whole southeast. What I ran into that puzzles me is this. The first project was a 2 acre lot in a shopping center. It was tied to the NC grid system. Great! The monument they tied to was about 8000' away. There is a perfectly good monument 300' from the corner! We did the original subdivision and tied to this monument. Still there. No obstructions within 400'.
The second project was a tied to a monument 14000' away and there are monuments ON THE PROPERTY!!!! Do you try to tie the closest monuments? I know in theory grid is grid, but why not use the monuments close to the tract you are surveying? The NCGS website has a map to pull up showing all monuments.
surveyorjake, post: 411373, member: 8349 wrote: Recently I've had two projects that were surveyed by out of state company's. One from Virginia the other from South Carolina. No big deal. We cover the whole southeast. What I ran into that puzzles me is this. The first project was a 2 acre lot in a shopping center. It was tied to the NC grid system. Great! The monument they tied to was about 8000' away. There is a perfectly good monument 300' from the corner! We did the original subdivision and tied to this monument. Still there. No obstructions within 400'.
The second project was a tied to a monument 14000' away and there are monuments ON THE PROPERTY!!!! Do you try to tie the closest monuments? I know in theory grid is grid, but why not use the monuments close to the tract you are surveying? The NCGS website has a map to pull up showing all monuments.
Depends on the quality of the monument, i wouldnt use an old third order NAD27 monument that was recalucated with a new NAD83 number, heck back in the old days I didnt use them for 27 control.
If you have the far away data and can calculate project coordinates before you get to the project why waste 10 minutes onsite tying into a closer one? That firm and client believe time is more important than quality. I would worry more to know if they even had a copy of your original subdivision for their work file?
Paul in PA
Is this an elevation issue or a location issue?
I believe from what's been posted here in the past is that the rule in NC is to tie a survey to a known State Plane monument that is near the site being surveyed. I can see where going 3 miles from the site to tie a monument might seem extreme, however published monuments by the NGS come with lots of caveats. A good example is a nearby small town, 2 miles to the east is a first order bench mark that was turned into a HARN point, it has new 83(2011) coordinates published and is also very good elevation control, on a hill above the town is a triangulation station that also appears in a list of local monuments by the NGS. The HARN point says it was surveyed using GPS, the Tri station says it was surveyed by classical geodetic methods (in other words, turned angles referenced from a base line during the NAD27 surveys).
And since there is a first order bench loop there are lots of bench marks published with lat, longs but these are scaled numbers pretty much useless.
The HARN coordinates will be pretty good, the Tri station probably within a foot for a first order station, this is a third order station, so.................
I'm not sure if the point of the NC rule is to just do a radial tie to the monument for the purposes of being able to add close stability to the survey (like swing ties for a section corner), or is it to establish a state plane coordinate, if the latter, I would tie the monument 2 miles east, if the former then the close one just up the hill would be the pick.
You need to be careful looking at datasheets, the third order monument publishes a lat long coordinate out to the 5th decimal place when the accuracy probably falls somewhere near the 2nd place. I wouldn't be surprised that the coordinate is more than a foot "off". But as a swing tie, it's sat there for 70-80 years so it's great for that.
The old triangulation stations had their NAD83(86) coordinates recalculated from observations, so they are a lot better than a simple shift from NAD27, and have been updated using the HARN measurements in the area.
But they definitely aren't as good as HARN or NAD83(2011). By my measurements, the old horizontal control in my area that did not have GPS remeasurements are about a ft off of what GEOCON2 would predict. It is 40 miles to the nearest point in the NGS data base that has both classical triangulation and GPS data, so that is well within their spec.
Bill93, post: 411406, member: 87 wrote: The old triangulation stations had their NAD83(86) coordinates recalculated from observations, so they are a lot better than a simple shift from NAD27, and have been updated using the HARN measurements in the area.
But they definitely aren't as good as HARN or NAD83(2011). By my measurements, the old horizontal control in my area that did not have GPS remeasurements are about a ft off of what GEOCON2 would predict. It is 40 miles to the nearest point in the NGS data base that has both classical triangulation and GPS data, so that is well within their spec.
I will generally see 1st order 27 monuments that have been recalculated to be within .5', I've only located a few third order monuments, but they don't work very well, which isn't surprising since they were not very good as 27 monuments either.
I have surveyed in NC and have tied multiple projects that were surveyed concurrently to a monument that worked for both. It is my opinion that the intent of the rule was to place surveys on the SPCS. If this is correct, I don't see why we would waste time looking for a monument that may or may not exist, undisturbed, in the location it should be found.
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Jweiss, post: 411437, member: 11740 wrote: It is my opinion that the intent of the rule was to place surveys on the SPCS.
If that's the case, why did they specify a tie to a physical (if remote) monument, instead of letting you get SPC from your GNSS unit?
Bill93, post: 411441, member: 87 wrote: If that's the case, why did they specify a tie to a physical (if remote) monument, instead of letting you get SPC from your GNSS unit?
Very good point Bill.
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I assume the rule predates common use of GPS, in those days the monuments were treated as "fixed" positions.
Bill93, post: 411441, member: 87 wrote: If that's the case, why did they specify a tie to a physical (if remote) monument, instead of letting you get SPC from your GNSS unit?
Many of the laws relating to ties to the NSRS were written when civilians had no access to GPS. Unfortunately getting legislation through to clean it up isn't a priority in many States. Worse yet is that Counties are using the archaic code as a template for ordinances.
We need to be educating ourselves and the people that produce policies we work with.
The NC rule is that surveys must tie to an NGS monument if one exists within 2000'. If not, you can tie to a centerline intersection or other prominent/permanent feature. Of course I am paraphrasing. I have always understood this to be a way to eliminate "floating" surveys within a colonial survey system. In other words the rule was put in place to establish a substantial POB, and not an attempt to put all surveys on the NC Grid. When the rule was established there was no GPS. So tying into NC Grid would have required two monuments with established NC Grid coordinates. This would have added significant costs to all boundary surveys at the time.
But the original question is why did the surveyor go so far to tie down the survey. Without knowing the specific area, my guess would be GNSS. The surveyor may have found/used the nearest monument that had open sky and setup an observation there and another point on the site with open sky and setup an observation there. Both running while he performed his traverse around the site boundary that included the site GNSS point. Yes, this is over and beyond the requirements of the rule. But his actions may have been dictated by the client and his scope of work, not just NC rules. ......purely speculation on my part.
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BushAxe, post: 411476, member: 11897 wrote: tying into NC Grid would have required two monuments with established NC Grid coordinates
I believe that if you have a single mark with coordinates you trust, you can orient the survey to the grid meridian with solar or Polaris observations.
Just sayin'.....
Here's the survey tie guidelines issued by the NC Board.
