Yes, it's less than 5PPM through the entire subdivision. 5PPM represents an elevation change of 200', .05' in 10,000' or .0005' in 100', not measurable in a subdivisional context.
Remember, you're calculating from state plane to ground individually. Presumably, your drawing lines are connected to XY coordinates in state plane and now the task is to individually recalculate each line, how is that accomplished and how are the CAD lines labeled?
No, see, that's the CAD problem. CAD needs coordinates, but once we reduce state plane distances to the topographical surface, we no longer have usable Cartesian coordinates. Now lat/lon and XYZ are unchanged, but they're on the ellipsoid, not the topographical surface.
That's why CAD drives surveying procedures and why it probably can't be overcome.
Mathematically and surveying procedure-wise, there's absolutely nothing wrong with what you do. Sure, I could develop an independent LDP for the area, but it wouldn't perform any better than what you have.
Actually, I'm a fan of yours. You know your work, you know your tools, and you're a real pro.
When I hover over a point on Google Earth I get Lat, Long, Elevation and it's really accurate in a world wide context. Sometime, maybe not too far in the future, there will be models similar to the Google Earth model that we survey on. True north at all times, precise ground distances between points and a CAD engine that draws it all. That's the dream, it's possible now, Eric Burkholder has developed a program to do it, I think it's not far off for everyone to get on something like that.
But it has to do CAD, drawings, engineering design, GIS, ect.
Of course, SPC will be a quaint anachronism.
Again, using state plane distances to compute acreage produces a meaningless number and you should know that.
Working in the shale plays of Texas, it was common to run in straight state plane grid for unit maps. In that case grid distances & areas were just fine, because the intent is to calculate mineral interest (and payments) by percentage of area. Scaling from grid to ground would yield the same result.
Surveying on the state plane grid does not mean using state plane grid distances as if they were on the topographical surface, and you should know that, too.
I don't think we get to choose what part of state plane we use. Perhaps prior to global reference networks and widespread use of GNSS, we could make the argument that azimuths were the primary way to "get on to state plane", with network accuracy taking a backseat to local accuracy - and in many cases network accuracy wasn't even along for the ride.
We're not setting up terrestrially on passive marks and observing an azimuth reference, then jumping off on a traverse, any more. At least not for 99% of our projects, I am sure there might be a few who are still using that methodology.
Once GNSS hit the mainstream, and especially once the NCN got up and running, the primary connection to the NSRS has been through published coordinates that we evaluate and constrain to. Everyone tells themselves that they're "surveying in SPCS", conveniently ignoring the fact that they messed with the coordinates (and lines in turn) after the fact.
When it comes down to it, I don't care about your basis of bearings. Project that job any way you please. If you give me the geodetic basis and your projection parameters that keep the grid at the topographic surface, and don't screw with your data after they have been projected, I'll just reproject and be on my merry way.
Google Earth is remarkable. Web Mercator uses a sphere with semi-major axis and semi-minor axis equal to the semi-major axis of WGS84 and a Mercator projection. It is prime evidence of how closely a sphere and an ellipse are to each other.
It may well be true that GNSS should have completely displaced plane projections of every kind, but that hasn't happened and, indeed, NGS is prolonging plane projections with its 2022 work.
SPCS were derived in order to simplify calculations, but as software has progressed along with drafting software, things have become more complicated.
@mightymoe I think a better example of small differences in area potentially being costly is zoning. For example, if my lot were over 5 acres most building permits would just be a matter of filing a form and paying a modest fee. But under 5 acres, everything needs a variance, which means going before the development review board, which may take months and incur $xxx in fees.
I need to correct an erroneous statement I made above. XYZ coordinates are not on the ellipsoid, except by happenstance. They exist in free space whether there's a defined ellipsoid or not.
Given that, a survey done in 3d coordinates could satisfy both ground distance and CAD considerations. However, calculated distances would be slope distances.
Here is the 3d graph of the three points DQ3133, DQ3134, and RW0581 used in one of the posts above,
Look at the differences between the XYZ coordinates between the NC plane and the MT plane in your post on 3/24.
Those differences are due to the International Foot in MT and the US Survey foot in NC.
XYZ users beware: After the 2022 changes become effective, old coordinate records in current Survey Foot states can't be used with newly published ones.
Fortunately, NGS datasheets don't show XYZ coordinates other than in meters.
They should add: furlongs, barleycorns, Smoots, & cubits.
Because, surveyors...
Yes. But using metric is like everything else we've discussed here. Solving a problem often creates at least one more problem
Yes. But using metric is like everything else we've discussed here. Solving a problem often creates at least one more problem
Older versions: Some feet, some meters, even logarithms
Fascinating old data sheet! It doesn't have the 3d XYZ coordinates; they had only 2 dimensions to work with.
When i did metrology work i used north east and up which made it easy with multiple measurements tools . And we didn’t care about gravity or which way water flowed for the testing we did. I used gps scanners laser trackers radial arm scanners x ray and some other cool toys. Working with xyz only is not complicated math but the distance inverse is point to point though.
Fascinating old data sheet! It doesn't have the 3d XYZ coordinates; they had only 2 dimensions to work with.
Z is there, you had to have Z.
In the NAD 27 days, I think, x was Easting and y was Northing. The terms Northing and Easting came later.
For DQ3133, NAD83 (2011) (Northing and Easting, or y and x, are:
while (X,X,Z) are
We can't compute these from lat/lon without ellipsoidal height, the missing element from NAD27.
This can be demonstrated empirically with NCAT. Take the lat/lon from the old data sheet, enter them in NCAT, make both input and output systems NAD27.
On the far right hand side of the output are X, Y, Z. They'll be blank because NAD27 has no ellipsoidal heights.
@mathteacher The wife got this shirt for my daughters birthday coming up April. She has her own egg business. Raises her layers . I just couldn’t help but to think of you when the wife showed me this weekend.
Nad27 was lat long only so you are correct. Clark 1866 ellipsoid which better fit North America. But does not work well with the global model and gps since it looks for center of the earth. When you have time to play use your math skills to play with north east up. I am thinking it might interest you . It could be a option for surveyors with the computing power we have.
We can't compute these from lat/lon without ellipsoidal height, the missing element from NAD27.
This can be demonstrated empirically with NCAT. Take the lat/lon from the old data sheet, enter them in NCAT, make both input and output systems NAD27.
On the far right hand side of the output are X, Y, Z. They'll be blank because NAD27 has no ellipsoidal heights.
And this is yet another reason why NAD27 needs to die. NAD83 is already on its way out, and there are multiple deprecated realizations of NAD83 that came after NAD27, so it's time to let it go.
If something that was originally on NAD27 (or even an older realization of NAD83) is important enough to resurvey accurately today, it's important enough to spend the time to resurvey and get it on the NSRS to perpetuate it in the future.
In the NAD27 days ellipsoid heights weren't used. The datasheet I downloaded explains quite a bit about how NAD27 was implemented and how it's to be used.
If you really want to dig into NAD27 I would suggest getting a copy of the booklet for North Carolina. Those can walk you through the fundamentals and they also have scale factors for interpolation.
I have a big map (somewhere) of the local NAD27 network which is illuminating.
About 15 miles NW of the office is a NAD27 monument called SE Base. There is a sister monument NW of it called NW Base. They sit at opposite ends of the topographic feature called Five Mile Flats.
I will assume there are similar monuments near your location.
Those monuments tell a story about the implementation of the network.
What this means and what the datasheet is telling you is that there are fundamental differences between 83 and 27. NAD27 is used quite differently from 83 and ellipsoid heights are not a thing.
The NCAT functions are an attempt to get on NAD27, but the monuments are the bible.
If you want to see the difference do a monument at your location and one at Helena, review the differences between 83 and 27 at each location, I'm guessing a huge spotlight will click on.
Reminiscing about (or trying to use) NAD27 is like watching vcr tapes on a 480p tube television. The resolution isn't there, and it's rather pointless to continue with outdated junk.
Yes, there are conversions that can be made, but you aren't making anything better than the limitations built into the system of that era.
The 1930's are gone, but apparently those people and their ideas are harder to shake than a time-share condo.
Why not also advocate for USSD, or NAD?
Well, yes. Actually, the methods for calculating state plane coordinates from lat/lon are very different along with the absence of ellipsoidal heights and different ellipsoids.
Now if you ask NCAT to convert from NAD27 to NAD27, guess what? The entered and computed coordinates will be identical.
But there will be no XYZ coordinates computed.
Also, there is a huge difference between survey software xyz and geodetic XYZ. The former are strongly related to a horizon-based system while the latter are determined by the spatial distance of the point from the center of the ellipsoid.
NAD27 xy is analogous to xyz in survey software. Changing the z does not affect x or y.
In XYZ, changing the ellipsoidal height changes all three coordinates.