So, I've come across a few surveys from a particular surveyor who's accuracy verbage is as follows:
NORTH CAROLINA
****** COUNTY
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I,(SURVEYOR NAME), PROFESSIONAL LAND SURVEYOR NUMBER
L-####, CERTIFY THAT THIS SURVEY WAS DRAWN UNDER MY
SUPERVISION FROM AN ACTUAL GPS SURVEY MADE UNDER MY
SUPERVISION (DEED BOOK ### PAGE ###) AND THE FOLLOWING
INFORMATION WAS USED TO PERFORM THE SURVEY:
CLASS OF SURVEY:B;
POSITIONAL ACCURACY:500 RMS;
TYPE OF GPS FIELD PROCEDURE: VRSRTKGPS;
DATUM NAD83 "2007", NAVD88;
GEOID MODEL; GEOID 03;
COMBINED GRID FACTOR: 0.9999466;
UNITS: US SURVEY FEET;
THAT THE SURVEY IS OF ANOTHER CATEGORY, SUCH AS THE RECOMBINATION OF EXISTING
PARCELS, A COURT-ORDERED SURVEY, OR OTHER EXEMPTION OR EXCEPTION TO THE DEFINITION
OF SUBDIVISION.?ÿ THIS PLAT WAS PREPARED IN ACCORDANCE WITH G.S. 47-30 AS AMENDED.
?ÿ
_________________________________________________
SURVEYOR NAME, PLS?ÿ L-###
?ÿ
Here in NC we usually us the 95% confidence level to express accuracy and I know of 2 methods of calculating it.?ÿ One using VRS and the other using OPUS.?ÿ However, I'm not so sure as to what this "500 RMS" is.?ÿ ?ÿAnyone else out there got a clue?
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Thanks,
Firestix
I'm not so sure as to what this "500 RMS" is.
That's the first thing that jumped out to me, too.?ÿ There should be units on that, and 500 doesn't seem to relate to the expected units.
I suppose there is no question that it is done with the proper SPC zone, although unstated, with SPC bearings and scaled to ground. There are some trivial things to pick at also, starting with punctuation, spacing, and "COMBINED GRID FACTOR" where I would want to distinguish CF from grid factor. But you can generally get the meaning of everything but that 500, and it is a better effort than many.
It has the earmarks of someone who is regurgitating lingo he does not really understand.
I'm sure you realize that the last 3 lines are a direct quote of G.S 47-30 (f)(11)(d). As such, it doesn't really comply with that.?ÿ I think that you are wasting your time if you spend it trying to figure out what this mental midget was thinking.?ÿ
For a class B survey in NC the Positional accuracy at the 95% confidence level should be .125'. Our board rules describe the certificate in .1607
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@adam
Exactly Adam. I've search the board rules and found Zero refrernce to the "500 RMS" blurb or any reference to RMS. I'm fairly new to the Licensed Land Surveying world (did a lot of GPS and Geodetic Surveying in the Marines) so what do yall do when you come across something like this?
Sounds like they're saying it's plus or minus 5 feet or so, and listing an exemption that allows that level of error??ÿ Just a wild guess.
Sounds like they're saying it's plus or minus 5 feet or so, and listing an exemption that allows that level of error??ÿ Just a wild guess.
I doubt that.?ÿ Possibly 0.500 but even that doesn't fit the requirements.
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He states a survey class for I assume North Carolina. By doing so he also ties to the accuracy standard for a Class B survey. He doesn't need to go beyond that. As far as the GPS information he is on NAD83 something epoch 2007, he is using NAVD88 elevations with Geoid 03. He is tied to the VRS and the scale factor to adjust to surface is .9999466.
the 500RMS is not necessary he already defined his accuracy with the Class B statement.
I wouldn't think twice about the statement he has it covered with one weird inclusion and one big exclusion (North Carolina Coordinate System?).
One other thing would be the NAVD88 statement, are there elevations given for this survey, if not I would remove that.?ÿ
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I've seen wwwwwaaaayyyyy worse than that one.?ÿ
I probably wouldn't give it much thought as long as you find all his corners within reason. How old is the map? If he is using the NCRTN recently he isn't using the epoch or geoid he listed. Unless, Perhaps he shifted to an older monument but if so he should show the monument information on the plat. Also, there is one item missing from the cert which is "Published/Fixed Control". If using the rtn you basically say rtn vrs. If he used a monument he needs to state which monument with the metadata.
This is a 2019 map and there is no published control referenced.
I use the same basic note on my plats as well, however I do give a horizontal and vertical accuracy based on my observations. My question would be how much is he relying on GPS to do the survey. I know where I am located in NC there is no way I can really do an entire survey using GPS, but I do still have to make the grid ties if within 2000 feet of a monument. Unfortunately in NC we don't seem to have any notes to put on plats for just using GPS to tie to state plane, so we have to use the crazy long note that we have.
