Iowa law requires distances on the horizontal plane whatever that means. The only plane defined in the survey code is state plane but absolutely no one practices using that definition. It's assumed to mean a horizontal plane at whatever point the total station is at. In the case of GNSS usage its assumed to mean a project plane approximating ground.
I would say limited in height more than size. You could create a sizable LDP that could include a number of mountain tops for example.
I'll bet all this talk amuses Loyal. He's Mr. Mountain LDP before it was cool.
Yes. Where there are saddlebacks that aren't swaybacks, it would work fine.
As you know, rapid elevation changes kill LDPs and ground coordinates computed from state plane coordinates. On the NC coastal plain, we could probably do a 50 mile by 50 mile LDP with no problem.
We could perhaps do something reasonable between Boone and Blowing Rock.
But between North Wilkesboro and Boone, probably not.
@mathteacher i 100% agree. That is correct that is what you asked originally. The issue is that some do not look at state plane coordinates the same way they were intended to be used. Reality is i see surveyors use them as if they are just coordinates and not on a mapping projection. I know they can use them correctly they have already proven they perform the math as they use similar equations every day. But it’s that maybe they are in such a hurry or don’t want to i have no idea. I stay in the dog house all the time as i make the necessary computations when i process jobs. But i have to deal with the issues on projects that are not mine and were not done the correct way and it becomes a this is how we always do it and that’s the way it should be done. It is very productive to devise a system that everyone does the same exact thing same exact steps on pushing the same exact buttons. And this stuff was established these procedures before some of the software could do it so easily like we have had for many years and today. So for some it doesn’t matter that Trimble Business Center or any other software can compute this so easily. Heck microsoft excel is easy enough also. Its just thats what was done and in surveying bucking the system is frowned upon at company levels. I was almost fired once because I discovered a company had duplicated tempature and pressure settings in total station and data collector then apply it again in office. So triple . It didn’t matter that both the data collector manual and total station manual specified that use one or the other. It was the way it was always done. I agree the math the process is not hard and i am not the brightest bulb myself. But I always said if i can figure it out anyone can. If the system is used as intended its one of the most accurate ways we can measure and position things next to true geodetic work. I am no cad guru so maybe thats the road block. I have worked on both sides geodetic and daily ground surveying. I didn’t not see the why a system like state plane was so great until i had done geodetic work. Utm and others. Once learned and saw how to handle everything the light bulb shined and now personally if i were solo i would simply do everything in a state plane and do whatever computation’s necessary to meet the state specific standards. I have followed one surveyor here that had his required coordinates in a certain county on the plat that i would say were true state plane. His bearings were state plane grid and his distances were ground and he had a good set of meta data notes etc that when i followed him it was only a difference of my measurements vs his and that was all within the rtk tolerances and traverse tolerances. So so minute it was negligible. Most of what I follow i see they have scaled to ground but publish the state plane ishhhhh coordinates as required and i can follow the boundary nothing wrong with the boundary information but the coordinates have a shift and sometimes i wonder if they know exactly how far they are shifted. I usually reverse engineer it and see if i can determine hiw they scaled. Some scale from a zero zero location and a combine factor for a county. Some scale in centroid of the property at an point and elevation not necessarily the average elevation or ellipsoid height. Some pick a point. Some use spreadsheets but most are not scaling distances they are scaling the northing and easting coordinates. They have spreadsheets set up to do this. I have asked . Now it doesn’t change the boundary survey just the coordinates themselves. And yes some probably have done this on jobs that a one combined factor is probably introducing distortion that maybe they don’t realize. I caught one of those approaches on a job i was troubleshooting. Once i showed the person why simply clicking in tbc at approximately the center of the site would not work in that situation they were like ohhhh. Now i see what you have been saying. I think the answer to your original question is not what is most understood but what is the most negligence use of the system might be better question. I think this has been a great topic for sure. I enjoy reading all the comments and seeing things. Remember i am told this all the time surveyors hate change. Look its 2023 and if it were not for rtk dominance a lot of surveyors would not be using state plane period. It would be as simple as setting up on a site assuming a north and east and off to the races. I started my career doing that using a compass for azimuth and or sun shots. Everything else was just assumed. Sometimes we just assumed north because we knew we were holding a certain line off a deed anyway.
OK, I see the problem between individual state plane distances converted to ground and CAD.
CAD is itself a plane coordinate system. It needs coordinates to draw lines. If we want ground distances out of CAD, we have to give it ground coordinates. If we use a single combined factor to derive the coordinates, the angles on the drawing will be state plane angles by geometrical similarity.
If different lines have different combined factors, CAD will have difficulty coping. Have to call in an AI shrink. The old plane table guys would throw up their hands and walk off the job.
Thanks for being patient with me. I had to make a lot of connections to get to the underlying cause.
Think of it this way, I recently did a subdivision of small lots kinda in the country south of town. These lots were about 8000sq ft. They were being offered at 120k. Seems crazy to me but I'm not the buyer. I do see houses being constructed there and they are nice looking. What the lots actually went for I don't know.
Anyway that's $15 per sq ft.
Using a state plane of 300ppm (6000' below ground) will change the sq ft per lot by almost 5 sq ft. Not a big deal, but that's $75 per lot, 150 lots and you just cost your client $11,000. All cause of a state plane fetish.
So, to correct that, your idea is to recalculate all the lines surrounding each of the 150 lots. Probably doing that using strictly state plane coordinates will cost at least the $11,000 to hand enter each number, check all the calculations, ect.
In a small, flat, low state the difference is probably not noticeable.
I doubt I would ever be taken to court over the $75 per lot, but I feel like doing the best for my client is important.
Well, that's sort of my idea. I would actually divide each of those separate state plane coordinate lines by its own individual combined factor to get the same length that I would measure on the ground for each one. I wouldn't redo anything in this case, though.
Again, using state plane distances to compute acreage produces a meaningless number and you should know that. 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.
But, even if the surveying software could do that, which it probably can, CAD couldn't handle it.
With your method, you get something very close to topographical distances along with state plane azimuths. Measuring a lot line will produce the CAD result, but turning the angles won't.
And that is a plane geometry relationship, not a surveying truth.
@norm VA has similar wording. I asked the question once and was told that the standards stated ground. I am getting a beer soon as i won the bet lol. Around 1930 ish I found where it was added that all distances were to be reduced to a horizontal plane. No where does it state ground. Prior to the 1930’s ish. I am still trying to do the research but many surveys were along the slope especially when measuring with poles up a hill. Not uncommon for any area I imagine. My date is approx. i was studying and came across the topic and lead me down the rabbit hole. I like researching this stuff. Anyway if one wanted to make a good case to argue with the way the standards are written one could probably do very well in arguing that since the state plane was adopted at about tge same time all horizontal distances were required that surveying on the ground could be a mistake from Assuming. And we should have all been on plane. But historically the surveys were on ground. But I imagine one of those good smooth talking lawyers could make a good argument either way. It was drilled into my head we measure horizontal distance at the surface for boundary work. We have approached the time in which we can measure so well and it’s not slowing down either. Can you imagine one can survey 20 miles a part and have confidence that those two points are within an error ellipse of a coke bottle top. Now to traverse that far if we fell within the come bottle itself we would be tickled pink.
Just off the top of your head, how long after each 150 lot is drawn and labeled would it take you to hand calculate each line, relabel them by hand, check it all somehow for errors and typos?
Remember, at the time you start the effort I'm already finished with the exact numbers and $0 for the client.
Now, Moe, I said above that I wouldn't change anything that's been completed. And you don't have the exact numbers; they're probably within a few hundredths or thousandths, but you really don't know, do you?
I'm not criticizing your work, but I do object to considering surveying on state plane to mean using grid coordinates as if they were ground.
Can you tell me the ppm error in any of those lines? Is it the same for all of them?
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.
