My favorite bench mark is labeled "JOIN".
Looks like Washington has one and Alaska?ÿ has four by that name. Unusual to see so many with the same designation in one state.
Sewer MHs here began in city datum, which is NGVD29 -3000 some feet. Then MH's were updated to NAVD88 when the city mapping was done. Each new new reconstruction job was to include a set of Azbuilt drawings, you can imagine how that worked out.?ÿ
Anyway, since we partook in the upgrading of the MH elevations during the mapping phase we have the early 2000 official numbers on NAVD88 with inverts. Then the GIS department re-located them with GIS grade receivers, now the GIS mapping is as accurate as you might expect. However, getting all local jobs on one system hor. and vert. that matches the topo has been bigly valuable. Since we have the MH's in our files that has also been valuable. I can't see not doing it for jobs requiring elevations. There is more time consumed messing with different systems than having it all on one.?ÿ
Can you think of any typical circumstance around any urban area of 25,000 or greater population where you would not take the time to establish good elevations?
Yes I can. Nevertheless, I do routinely tie almost all my projects to the national datum both horizontally and vertically, set durable monuments, and retain the raw data. I'm always thinking of my work as the basis for the next job in the vicinity. So while there are surveys that just don't have the need or the budget for tying to the NSRS, there is always the possibility of them getting upgraded in the future.
Superior widgets are wonderful things.?ÿ Let's dictate that everyone own a $90,000 widget, know how to use every function for which it is capable of performing, use "my" favorite software, provide proof of 50 hours of pre-approved-only continuing education each year and carry $20,000,000 in professional liability insurance before they are allowed to offer to perform land surveying for the public.
Don't worry.?ÿ That will clear out all of those annoying "little people".
My favorite station name is INSANE ECC in DC. I occupied the station in the 1970s lovely view. It is atop a building on the St. Elizabeth??s Hospital. Originally named Government Hospital for the Insane. Glad they let us leave??
I'd settle for anyone performing land surveying to be well-versed in the history of our national datums, how they relate to each other and local datums, and how to document procedures, adjustments and any anomalies uncovered regarding said relationships.
If someone doesn't want to tie their survey to an existing datum, that's their prerogative. I find it beneficial as well as simple, even with decades-old equipment. If workflow does not permit, that's fine.
Personally I like the current tech and its capabilities. But it's pretty useless without an understanding of what's going on under the hood, so I'd say knowledge is king.
Another surveyor had this little scene play out one day almost 40 years ago.?ÿ He had performed a survey for a fellow by using a total station and running a traverse rather that attempting to directly measure along the boundaries.?ÿ The client asked how that worked.?ÿ He explained to the client about the mathematics involved and how he could even shoot through areas with foliage (shooting through the trees---is what he said) with excellent accuracy.?ÿ Sometime later the client called him to do another job, but in this case he wanted markers set every 100 feet along a mile-long boundary.?ÿ The surveyor was well aware that this was a very old tree row with trees of three and four feet diameter being common and very solid undergrowth anywhere near the tree row.?ÿ He did his best to arrive at what the final bill might be.?ÿ When he gave the client that estimate the client became enraged and called him some rather colorful names associated with being a thief.?ÿ When the surveyor tried to explain what all would be required to do the staking as requested, the client cut him off and said, "All you have to do is get on the boundary line and shoot through the trees with your gizmo.?ÿ The client had misunderstood what the earlier comment about shooting through trees meant.?ÿ He honestly believed?ÿ the magic beam was literally drilling a hole through every obstruction.
As ridiculous as that little story is, that is exactly the foolishness that gets into the heads of non-surveyors.?ÿ Then those non-surveyors become minor bureaucrats who specify expectations/design requirements/standards for any work to be performed for whatever little bureaucracy provides their paycheck.?ÿ We recognize the foolishness immediately ( all distance numbers to be rounded to the nearest 10,000th of a foot).?ÿ When their expectations dictate the procedure (ALTA of 100 acres of forest using a scanner for every step of the process) what they are doing is setting a standard to be awarded the contract that only a small fraction of survey companies can supply while the information truly needed to provide excellent data for development of that 100 acres could be provided by nearly all survey companies in a certain area.?ÿ
I started my surveying career in NH and ME where few physical NGS BMs and almost no CORS stations existed.?ÿ My attitude towards ties to SPCSs was nearly identical to HC's upon my arrival to North Carolina.?ÿ
After a few years of surveying in NC, with a robust CORS network and plentiful physical BMs, I realized that my former attitude was more of a justification for not pushing myself to do more for myself and my clients.
Attitude is infectious.?ÿ Here in NC, where SPCs originated, the attitude to get everyone on the same datum has spread beyond NCDOT and into our licensure boards into our PLSs.?ÿ While it's true that a grid tie requirement has the potential to negatively impact PLSs who choose not to, or perhaps can't, invest in GNSS, the advantages to the public greatly outweigh the burden. NC also accepts a tie to physical BMs for those unwilling or unable to change with the times.
One of the greatest advantages I've seen is the ability to instantly provide an orthoimage behind a plat.?ÿ This is perhaps the best value to the average residential client who has no clue how to follow an unmarked line through the woods and find his corner.?ÿ Yes you can pirate a GE image and best fit it, but compared to a high quality ortho, it looks cartoonish.?ÿ Go ahead and keep on giving clients the minimum if you want, eventually they'll discover the utility of an imagery overlay.
Since committing to tie every project to NCSPCS, I've been able to partially solve a problem that has vexed me since I began surveying: How can I inexpensively mark a boundary line, in a somewhat permanent way, so that my clients can understand what they own and where it is??ÿ While its use is somewhat limited on small lots, simply exporting my final boundary line and the found or set monuments in a Google Earth kml file goes a long way to solving this problem.?ÿ It takes minutes for me to do, it can be emailed and even unsophisticated smartphone users are capable of taking advantage of it.?ÿ My views on Grid ties have evolved from, "What a waste of time", to "Why on Earth wouldn't you be doing it if you care about your clients?"?ÿ?ÿ
https://en.wikipedia.org/wiki/Law_of_the_instrument
?ÿ
The possessor of said "hammer" becomes obsessed with the thought that all the capabilities provided by said "hammer" are essential and that importance must be pontificated to the ignorant client while justifying the invoice equal to half the value of the client's house.
Due to the large amount of confusion about what exactly constitutes NAVD88, my vertical datum notes will?ÿ usually read something like:
?ÿ
What exactly is the confusion with NAVD88??ÿ I do agree that you should note how it was derived but I don't it is not like there are all sorts of flavors of NAVD88 like there are with NGVD29.
Years ago Oregon had a platting requirement that every plat have a tie to 'ONE' geodetic control point but the plat did not have to be on SPC.?ÿ The thinking was that the counties could use this in developing their GISs.?ÿ One of those rules created by someone without any real knowledge on the subject without input from those whom do.?ÿ I was eventually removed from law.
That being said, with rare exception, all of my projects are done on SPC or LDP based on ties to the NSRS.
I didn't phrase that very well.
There are actual NAVD88 benchmarks in the NGS IDB that were part of the original geodetic levelling campaigns. There are marks in the NGS IDB that have NAVD88 elevations derived from GNSS observations and an NGS-developed geoid.
There are also local benchmarks for cities and municipalities that may have been tied to NAVD88 benchmarks with differential levels, or maybe with GNSS methods, either of which may not have been rigorous or maybe did not check into other adjacent marks. Some of those networks have substantial errors or biases.
Then there are benchmarks set by surveyors and other individuals and entities which may use a combination of any of the above, or possibly an independent post-processed static survey. Some may use an outdated geoid, or hold the elevation of a mark that has subsided.
So while all of those BMs may be related to NAVD88 in some way, that doesn't mean that they agree with one another, or even with the nearest physical BM also claiming to be NAVD88, or even the adjacent survey which used a different method.
Yet a survey or planset may use any of the above types of marks as project benchmarks, claiming that the vertical datum is "NAVD88" without any other information. This makes it difficult to both discover the provenance of the elevations depicted and determine the best way to verify them when needed.
It's not that the datum itself is confusing, but that there are numerous ways to derive "NAVD88", not all of them equivalent or consistent. The term gets tossed around a lot without the metadata needed to evaluate it.
@rover83?ÿ
That is not really a problem with NAVD88, just bad metadata.?ÿ
It is more important that the interrelationship of your project control meets the precision necessary for the project.?ÿ I don't think you need to run first or second order differential levels from an NGS benchmark to meet these requirements.?ÿ The main reason for stating the datum is place it in a general reference.?ÿ In Portland, there are four (4) possible datums ( Columbia River Datum, City of Portland, NGVD29[47] & NAVD88) and all are significantly different.
On a side note, physical benchmarks found in the NSRS are not always reliable, specially out on the west coast.?ÿ I once worked on a small scale LiDAR verification project covering about 450 miles of mainline railroad through CA.?ÿ The railroad had sent out one of their field engineers to do a bit of checking and found what they thought was a significant bust.?ÿ What it was was 30+ feet of subsidence over the 50 years since the line had been run.?ÿ I for one can not wait for the new adjustment and gravity models.
The more frequent issue I've seen is between NAVD88 and OPUS/CORS
@rover83 John is spot on. We need to remember the 3 D's of vertical work.
Datum. Which one?
Derivation. Source station(s)
Data. Type, treatnent, and quality.
In Chicago a really elevation is Lake Level. At least it used to be. Control had both MSL and LL.?ÿ
https://content.govdelivery.com/accounts/USNOAANOS/bulletins/2ef03a8
FYI
For those who are getting the static data anyway, and using GPS derived elevations??
