With so much data available via GIS every topo project we do is on SPC in my area. The main reason some topo projects around here are on assumed datum is for the PLS to retain the layout or atleast force the phone call for BM and control. About 90% of the construction plans do not have a BM or a baseline. I talked to several Engineers who were told not to place BM on the plan by their own surveyor. It sucks, but true.
Lately we see many Engineer plans drawn on a GIS aerial image with GIS lidar contours. No boots on the ground.
The main reason some topo projects around here are on assumed datum is for the PLS to retain the layout or atleast force the phone call for BM and control.
Ugh. That is the truth.
I've been on both sides of topo and construction throughout my career, and I still can't figure out when the bulk of topo surveyors and the construction surveyors collectively decided to remove "establish tight control" as a line item from their contract, try to dodge the work, and thus not get paid for it. It's like a game of hot potato, except if you get the potato you get...money.
Do it right and make sure you get paid for it, or tell the client that it wasn't in the scope. If we held the line as a profession we'd all be better off.
@stlsurveyor Nice. If he ran ground traverse already he needs a lat and long ellipsoid ht. He first needs to reduce his ground distances for mean sea level aka now ellipsoid distances then he can go to grid. I have no experience in NY. But one thing software has done is make it so easy that most people have not done the math and understand the seal level reduction now ellipsoid reduction. ?ÿIt was a FS exam question also. Grid to Ground terminology has its cons for terminology use. I was qc an old project not long ago and i quickly spotted that they had used the Scale Factor on the ground distances. And not the combined scale factor. I asked if they had calculated the elevation factor and combined scale factor. ?ÿSo in essence they had reduced well they went the wrong way as well using the grid to ellipsoid and applied that to ground measurements and called it Grid. Every surveyor should have to calc a few traverses making all corrections by hand so they know what??s going on under the hood. ?ÿI think even doing the corrected ZA from different in ht etc. have a scale table . ?ÿThat would really help in understanding for sure.
The term MSL was associated with NAD27 and is usually not used nowadays except as an inaccurate carryover in aviation.
The elevation factor should ideally be calculated from height above the ellipsoid, which is reported by OPUS and probably most other GNSS software. The error from using elevation above the geoid is probably not serious, but avoidable.
He should be able to get two points converted to state plane at each end, then it's a simple inverse to get the scale factor.
There isn't any need to calculate elevation or grid scales.
I haven't figured out a combined factor in many years.
To get a project scale factor it's ground divided by grid for some programs, grid divided by ground for others, he will have both numbers and should use them. Then I would take all the points and simply scale and rotate the figure.?ÿ
@bill93 Yes sir. Even Trimble Access under the advanced geodetic settings has it termed both ways. You are correct it is why i used aka when describing above. Because so many use it loosely unfortunately. ?ÿWhen the first datums were created it was assumed that all distances would be reduced for sea level correction. Some still assume that state plane was created to be within a 1:10000 however that was assuming distance was reduced and that 1:10000 was grid and geodetic distance or ellipsoid distance now. ?ÿI hope I am wording all this correctly.
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yes OPUS or any gnss system should yield ellipsoid heights easily. If not a simple visit to NGS site and use of the tools should help anyone convert from a grid coordinates to lat long ellipsoid height. I am kinda hoping when the new datum??s come out that scale factor elevation factor etc. get some much needed clarification definition. ?ÿSo our slang ??surveying slang? doesn??t cause confusion. MSL is still an issue with a lot of folks. Even younger folks use it loosely and do not have a basic understanding of it. ?ÿ
There isn't any need to calculate elevation or grid scales.
If he's going to go through all this trouble in the first place, why wouldn't you advocate he complete the process in its entirety and/or properly, to get on SPC? He is doing topo (elevations) too. I know he's not chasing 1-2mm of precision/accuracy, but "C'mon, man!"
It's like those surveyors that go through all the trouble to run an extensive traverse, but don't record the measure-ups...
5 seconds worth of effort can add so much more value, whether you need it "right now", or not.
I am kinda hoping when the new datum??s come out that scale factor elevation factor etc. get some much needed clarification definition. ?ÿSo our slang ??surveying slang? doesn??t cause confusion. MSL is still an issue with a lot of folks. Even younger folks use it loosely and do not have a basic understanding of it. ?ÿ
I dunno, I think all the textbooks, seminars, and NGS publications are pretty clear. In my experience, it's a matter of people not using the terms correctly, or flat-out not knowing what they are doing.
I've lost count of how many times I've heard the combined scale factor referred to as just "scale factor" (which is ambiguous) or "ground scale factor" (confusing) or even "grid scale factor" (just incorrect). I've seen surveyors insist on using the grid scale factor rather than the combined scale factor to bring a project to "ground", or reference their site calibration scale factor (computed from calc points, not ground points) as their "ground factor".
When we start throwing additional terms in there like Combined Adjustment Factor (which is usually - but not always - the reciprocal of the CSF, and what is actually applied to grid distances to bring them to ground) it just gets even messier.
Words mean things, especially technical terms, and we have to be absolutely clear about what we are doing when we mess with data in post-processing.
Even if our software gives a non-standard or goofy name to standard terms, we need to write our datum notes and metadata using standard language.
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(Edit to add the obligatory "Get off my lawn!")
Some of the best advice I ever received:
"We live in a 4D geospatial world. The sooner you accept that and get comfortable with the nuance of it, the better off you will be as a professional."
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Don't know what you're talking about.
He is getting on state plane.?ÿ
That's the whole point, he is getting state plane on both ends of the traverse and putting the entire traverse on state plane.
This isn't difficult, no reason to make it difficult. State plane was designed just for this. Been doing similar calculations for more than forty years now,,,,,,,,lllllloooonnnnngggggggg before the button pushers showed up with black boxes.?ÿ
@rover83 Thats because you read. ?ÿNot everyone reads. Text books ngs publications. Go to further training. ?ÿStudy ask questions. ?ÿNot everyone does that. ?ÿAnd not every college course makes it through all the material to educate one on that. Example. ?ÿWhen I took advanced geodetic course in college. It used the NAD27 approach. ?ÿAlmost every person came out of that class not understanding the ellipsoid of nad83 in the grid vs geodetic calculations. Only reason I knew was because of the Defense Mapping School and reading more on my own. Things like geodesy for the layman othe publication. Attending ngs classes webinars ceu pdh. I agree that it??s plane if one studies all the material. I am a little slow so every-time i re read or dive in and study i get a little more. ?ÿI wish more people did pay attention but it is simply not reality. Sure some know the buzz words but like I mentioned above when you look at data and quickly identify that a scale factor doesn??t mean the same to everyone. ?ÿI like that you pointed out a site calibration scale. ?ÿGeezers we could discuss this disaster all day. Try a site calibration with 4 points almost in straight line with a .991xxxxxxxx and they call it good. Because residuals fell somewhat low or good enough. Fix that to 1 and you see how well gps observations met existing control. You are right on. Just remember not everyone takes the time to study and improve. Its a how fast can you get the data into the office kinda world. It checked in cad so its good. I enjoy reading your write ups. You do well in communication by writing. Would love to sit and pick your brain over dinner.
There isn't any need to calculate elevation or grid scales.
I haven't figured out a combined factor in many years....
If you don't compute the elevation factor, the grid factor, or the combined factor....what are you computing?
Straight from Michael Dennis at the NGS:
"Total linear distortion of grid (map) coordinates is a combination of distortion due to Earth
curvature and distortion due to ground height above the ellipsoid. In many areas, distortion due
to variation in ground height is greater than that due to curvature."
Ignoring either source of distortion is just poor practice, especially when we have readily available tools to compute both.
Been doing similar calculations for more than forty years now,,,,,,,,lllllloooonnnnngggggggg before the button pushers showed up with black boxes.
What is this fetish with calling anyone who uses a software program a button pusher? Do you use a pencil and paper without a calculator, and hand-comp the equations from the NOS NGS 5 every time you need a convergence angle or scale factor?
I've written programs in Matlab and Python to use those equations for various purposes, and I've checked them by calculator when my code was throwing some odd results, but I've never done them by hand because...why would I? I have better things to do with my time.
I've been doing this for nearly twenty years, and I've gotten more efficient in that time; I plan on continuing to do so.
I don't care whether someone relies upon software to do tedious calculations, I care whether they understand what that software program is doing.
@rover83?ÿ
Yes. I came to surveying terminology late and learned from NGS, books, you guys, GISers, trial and error, etc. Here's a snippet from a Data Sheet:
Notice there is a scale factor, an elevation factor, and a combined factor. There is no "elevation scale factor" nor "combined scale factor."
CG0981! - Elev Factor x Scale Factor = Combined Factor CG0981!SPC AZ E - 0.99974534 x 0.99990499 = 0.99965035 CG0981!SPC AZ C - 0.99974534 x 1.00016154 = 0.99990684 CG0981!UTM 12 - 0.99974534 x 0.99964263 = 0.99938806
Now a lot of this was determined by mathematicians, most of whom had never held a rod, stretched a tape or chain, or sighted a heliotrope.
But here's the thing. The scale factor is the ratio of an infinitesimal distance on a map projection to its corresponding infinitesimal distance on the reference ellipsoid. It is constant and calculable for any point whose geographic and/or map coordinates are known along with the map projection and the reference ellipsoid used. It depends on nothing other than mathematics. It is unaffected by crustal motion or other physical processes.
NCDOT road maps include the following notation:
These maps are smaller representations of the NC State Plane, which has an approximate scale of 1:1. The reference alludes to the fact that distance scales are not constant between every pair of points.
The elevation factor, on the other hand, measures the vertical distance between the earth's topographic surface and the reference ellipsoid at a point. Knowing the map or geographic coordinates of a point does not give enough information to calculate an elevation factor. Thus, although the elevation factor is a ratio, a mathematical quantity, it is not a "scale factor." It cannot be determined without reference to the topographical surface, a non-calculable quantity, and is thus not a scale factor.
The combined factor, the product of a scale factor and a non-scale factor, is likewise not a scale factor.
The terms "elevation scale factor" and "combined scale factor" are so embedded in surveying terminology that they now appear in equipment manuals. I think, and someone can probably find an example, that Michael Dennis has used one or the other or both terms in his 2022 papers.
It's interesting to note that "sea level factor" does not include the word "scale." In essence, it is used as a combined factor, as it converts between ground and map distances. Those old guys back when were far smarter than I am and they knew that the geoid and ellipsoid were different, but they didn't have sufficient measurements of the geoid to separate it out and NAD27 fit the US very well. The result is the same as assuming geoid height to be 0 everywhere.
So, it seems likely that inserting "scale" everywhere came about with or after NAD 83 and NAVD 88. Perhaps when that last old persnickety wordsmith at NGS dies off, scale will intrude every ratio in the Datasheets, or whatever replaces them.
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@mathteacher You have an attention for detail. You are another on this site I would love to sit with. Yes you are very much correct in how all the terminology that is used by manufacturers, instructors, even I blame myself many times on doing some type of verbiage to try and relate something in a way so someone gets a basic understanding that I know has no idea what goes on in the box. ?ÿMatLab is one awesome tool. I am not a coder type person but have used Malab to aid in speeding up task over time.?ÿ
Now back to bouncing across the field tedding hay. Its not easy keeping tractor straight as I try and educate myself as I farm. But what a great classroom. Fresh air bugs sunshine and reading an this site. If I had a good computer I would just sit down with a traverse set of data and write it all out for the calculations but my iPhone is about as good as it gets. I know the ngs pubs. One i have saved from before i was born I believe has some great examples for many calculations. I can??t think of the name. It shows the formulas and gives exams. Some ngs pubs give definitions and formulas but no examples. Not that is the point but a good easy to follow cheat sheat would probably help many.?ÿ
@rover83?ÿ
What in the world are you going on about?
This is simple, basic, easy.?ÿ
He is getting a SPC coordinate on the ends of a finished?ÿGROUND?ÿtraverse that's completed and adjusted. All that's needed is to inverse between the ground coordinates and the grid. That relationship is the scale factor.?ÿ
Holy moly, this isn't that difficult, what he heck is this about NGS books, Micheal Dennis, Matlab, Python, it's a word salad that's unneccessary for this simple, simple, simple SPC conversion. All the work is completed, he just needs a couple of points for translation and a couple of checks.?ÿ
This is SPC surveying in it's simple form, as it was designed to be done.?ÿ
It's 800' long!!!!!!!!!!!!
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Sounds like a reading comprehension problem to me, or maybe you're just being disingenuous.
I made it clear early on in the thread that a simple translation/rotation/scale may be warranted depending on the circumstances.
Later on, I was specifically responding to your implication that it is unnecessary to calculate grid, elevation, or combined factors at all and that people who do are "button pushers".
I quoted your own post for reference if you're having trouble following along. Clicking on the quoted text will take you to the origin post.
This thread is going in circles.
A ground traverse to SPC should??ve ended with 3-4 replies. It??s a straight forward transformation. HP41 survey pack could handle it. And it??s a small site.?ÿ
