Someone made the analogy that it's like pin cushioning. They don't understand the weaknesses of the equipment or methods used and have an understanding of the errors inherent in the process and significance of the actual precision that can be achieved.
They're paid to know that and should be questioning the edicts they are enforcing. But they're not. And it's our fault for not educating them??ÿ
@oldpacer pin pricks? Now that sounds pretty accurate ground control.
Since I am dense explain to me how NGS got the money and man power to run level loops? Please undensify me.
Pin prick control. That's a new one on me.
@skeeter1996?ÿ ?ÿWhen you have not been around very long or have much experience surveying, new ones come easy.
@skeeter1996?ÿ ?ÿWasn't trying to insult you. You just had a bunch of knowledgeable people trying to help you but you could not get over your complaint that NGS is no good and that local official are out to get you. Your problem has NOTHING to with inaccurate NGS benchmarks and your local official is doing EXACTLY what local officials are trained to do. You have an unpermitted building built below the base flood elevation. FEMA has a big problem with that. Instead of blaming a bunch of people, fix the problem and move on.
@skeeter1996?ÿ You are correct, it was accurate and the shoe fits. NGS is a government organization, when the need money, they tax you. They get the manpower from private contracts administered through Water Management Districts or by using state field crews like DEP or DOT. It is amazing, as screwed up as the government is, they can provide such accurate control monumentation.
@oldpacer Thanks for adding additional ammunition. DEP and DOT crews are and were not qualified Differential Leveling personnel. At best they may knew a little bit about slope staking. I doubt any of the original NGS leveling crew people are still alive. When NGS upgraded their benchmarks from NAVD27 to NAVD88 they didn't go out and re-observe them. They recomputed them using interpolated values mathematically. The newest NGS benchmarks set in my area are late 1970's vintage. The Surveyors that ran the levels over them are all probably dead now. I would sure like to have a beer with one of them and learn a little history about their work routine. The technology and surveying equipment have changed significantly since the late 1970's. That's almost 50 years ago. I did have a chance to briefly chat with an old GLO (BLM) Surveyor Roy Bandy before he died. The crews back then were poorly educated farm kids. Certainly pretty unqualified to do error analysis of Differential Level Loops (If in fact they did run loops).That's probably why we're probably having accuracy problems with the benchmarks today.
That aside I believe the FIRM maps were never physically controlled using NGS benchmarks. Perhaps pin pricking is a magical method for doing that.
Some of the biggest survey problems in my State were created by old DOT Professional Engineers that had absolutely no surveying skills what so ever. I suspect you maybe one of those. The educations of the Survey Cadre today greatly exceeds that of the 1970's.
So could you start a new thread and explain how the pin pricking method is such an accurate ground control method. It would be quite educational for us Densiods. I'll admit I'm not familiar with that Control method and how it works vertically.
Your nickname says it all. Keep on pacing Buddy.
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@oldpacer Please quote where I implied NGS is no good. The Local official is not out to get anybody. He does not understand that the materials he is using are not accurate enough to enforce the precision he's doing. Evidently you and your knowledgeable people are of the same mentality. If we're labeling people, pin cushioners probably fall into the same category. FEMA has no problem with buildings below the Base Flood area. They produced FIRMs to protect the public from unscrupulous Insurance Companies, not to regulate community expansion. FIRMs are the only tool Communities have to regulate floodway construction. They're misusing them.
I'll restate my argument. NGS benchmarks and FEMA FIRM maps are not accurate enough to enforce Flood Plain Regulations to a a tenth of a foot, a foot, 5 feet, maybe not even 10 feet. Not as you accuse me in your post.
It's not my problem to fix, but I think I have an obligation to bring it to their attention they have a problem. Which I suspect they know, how can they not. I guess they have other priorities.
I've resisted the urge to be rude to you, but responding to your posts serves absolutely no purpose that I can detect. Are you McMillan mascarading as Oldpacer?
When NGS upgraded their benchmarks from NAVD27 to NAVD88 they didn't go out and re-observe them. They recomputed them using interpolated values mathematically.
NGS didn't use "interpolated" values.?ÿ They used the original observations, also including newer data with the old, and re-did the network fitting analysis.?ÿ The original observations were done with the best instruments that could be made using every control and correction known to man. They did loops and had very tight closure tolerances. Today's digital levels make it easier but probably no better.?ÿ Thus any motion of the marks in the intervening time was not accounted for but in every other way the data was as good as possible.
@bill93?ÿ
Well that's not what the data sheets say. The correction was calculated using the geoid model available at the time. Normal leveling routine would require loops, but I know there were routines in use using two wire readings that eliminated return loops.
I admit I'm ignorant of the procedures they were using.?ÿ GLO land surveyors were suppose to do return ties, but they didn't always do that. Elevations were pretty much ignored until Flood Elevations became common. I never used them until then. We use to pound a nail in?ÿ a tree call it 3000.00 and start off from there.
So, you automatically assume farm kids are poorly educated and stupid, do you??ÿ Your ignorance is showing.?ÿ Give it up.?ÿ You do not have a grasp on the reality of our world.?ÿ You have yet to find one poster here who agrees with your line of thought.
Well that's not what the data sheets say. The correction was calculated using the geoid model available at the time.
Yes, there are a few marks that used VERTCON and were not part of the NGVD29 to NAVD88 master readjustment. Relatively very few.
What is one of the PIDs you are referring to, and was it VERTCON?
@bill93?ÿ
The point is Bill, the NGS didn't physically go out and reobserve the benchmarks. The readjustment was simply a probably complex mathematic procedure. The benchmarks still have error in them. They weren't checked until us Surveyors started verifying with OPUS. NGS agrees and has asked Surveyors to directly observe specific benchmarks they've selected with GPS and submit the OPUS results. The Latitudes and Longitudes were scaled for the NAVD88 readjustment. I would guess that's alot more precise with the OPUS observation.
There are only three posters that are regularly biting at my heels. Two of them are bonafide wackos. Bill is the only one that apparently has any legitimate knowledge.
I'm guessing you three are what drove McMillan away. I'm tempted to follow in his footsteps. What initially was a very interesting subject has turned into three posters attacking me personally. I've posted a complaint with Wendell who has just ignored me. You three appear to be his favorite dogs.
- @bill93?ÿ
The point is Bill, the NGS didn't physically go out and reobserve the benchmarks. The readjustment was simply a probably complex mathematic procedure. The benchmarks still have error in them. They weren't checked until us Surveyors started verifying with OPUS. NGS agrees and has asked Surveyors to directly observe specific benchmarks they've selected with GPS and submit the OPUS results. The Latitudes and Longitudes were scaled for the NAVD88 readjustment. I would guess that's alot more precise with the OPUS observation.
They weren't checked until us Surveyors started verifying with OPUS.
OPUS measurements of marks with NGS data sheets does NOT change their NAVD88 values.?ÿ The OPUS measurements are to help build a new 2022 datum that takes out the tilt across the country and refines the geoid model.
The Latitudes and Longitudes were scaled for the NAVD88 readjustment. I would guess that's alot more precise with the OPUS observation.
The imprecision of the scaled lat-lon hasnegligible effect on the elevation calculations. A geoid model does not change measureably with the typical 100 ft or less horizontal error except maybe at the steepest mountains.
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That's a duplicate post to which I replied on page 2.
@skeeter1996?ÿ Honest question.?ÿ Do you know what he meant by the pin pricks??ÿ The aerial company would hand you a stack of aerial photos.?ÿ They would take a tack and punch a hole in the photo at their desired location for you to put a x,y,z on it.?ÿ On the back side of the photo, they would circle the hole and write an explanation down as to what it was they wanted.?ÿ Such as NE corner of concrete.?ÿ Or CL end of a paint stripe.?ÿ These are done a little bit differently now.?ÿ I apologize if you already knew this but it seemed from your response that you hadn't experienced this.?ÿ I've always loved doing aerial control.?ÿ Gravy.
@david-livingstone The Counties require Location permits for any new construction. If you erect a structure outside a Flood Plain without a Location Conformance permit they ignore it. If you constructed it in a Floodway and you can't get "LOMA'd" out of the Floodway they send you a letter giving you one year to remove the structure or raise it 2 feet above the BFE with other requirements to keep it from floating down the river. The point of my post was that FEMA FIRM maps are meant to provide a uniformed guideline to calculate Insurance Rates. A FIRM map's purpose is not to provide Flood elevations to an accuracy of 0.1 foot to regulate construction in a Flood Plain, which Counties are doing because someone has instructed them it's proper to do so. There is no mathematical rhyme or reason to the location of a Floodway boundary. Recently FEMA has produced a "Stay Dry" app for Google Earth that can be scaled on and can graphically show the Flood Plain boundaries locations. Prior to that it was impossible to trace that boundary on the ground. The Flood Plain boundaries are not following contours, topographic features or anything else describable that would be a predictable water boundary. It's a cartograhically produced feature which I feel is unretraceableon the ground, yet the County now wants the distance from the structure to the Floodway boundary..
