How many of you have found NGS markers

I found and used them many times but not since about 2000 when CORS become useful. With OPUS they are about obsolete except for BM's but in my rural area the BM's have become about useless also. About the only use for them I'd have is if they were referenced into previous control work that I needed to use or tie into. I don't do any flood certificates (live in desert for the most part).

We have found and used many of these over the years. We have found some that were listed as "not found" on the datasheets.. Found some to be destroyed, etc. We have run level loops through some of these and checked within hundredths, even miles apart. This was necessary in some of our communities that dealt with flood zone mapping, to prove we were on a datum (CORS at the time in Michigan was a couple tenths different than the published NGS NAVD88 values).

The brass ones set vertically in a church's brick wall are always my favorite.

We found one a few weeks ago that did not have a reported recovery since it was set in 1935.

I did an opus, but the opus elevation was not giving the geoidal height...

so I wanted an independant check into some local datum, also to double check what I was doing. Then, I found many were markers were gone.

N

There's probably 10,000 bluebooked NGS monuments within a 40 miles of my office. The State DNR, County, and NOAA continue to set and blue book monuments all over the place around here.

I use DSWorld to see what marks are available. You can submit destroyed marks through the program and update found ones as well

http://www.ngs.noaa.gov/PC_PROD/PARTNERS/index.shtml

Thanks! I'd like to get a govt grant, to go and update them...!

And, to retrace the GLO, in my area!

🙂

N

> Thanks! I'd like to get a govt grant,

Wouldn't that make you a socialist?

:{:

DSWorld will also allow you to submit new positions from hand-held or RTK GPS solutions for bench marks that currently only have scaled horizontal coordinates. You can also submit digital images of marks that will be posted to the datasheet.

They find us.

When we use CORS

I'm in northwest TN. I have a 3 receiver set of ProMark 3's. If you're not familiar with the ProMark3, they're single channel so I can't get an OPUS solution and I have to post-process. I set the base on a known point and establish a two point baseline at every job to put me on State Plane & Grid North for TN. I have several points in various locations that I have either gotten an OPUS solution on from borrowed/rented equipment or that I have redundancies on with my own equipment. There are 4 NGS monuments near me that I use frequently and 6 more that I use every once in a while. Sometimes I run on 2 NGS monuments with one on my site then move 1 of them to the site so that I can check my equipment's results on calculating the other NGS monument. I am consistently impressed with the results and accuracy of my equipment. Just recently I completed a 146 acres survey where I established my baseline from a trusted nail that had been set two years ago off of an NGS monument. Another local surveyor had published State Plane coordinates for a 320 acres survey of a farm that adjoined my west line. Their published coordinates were on the west side of their 320 acres and my base line was on the east side of my 146 acres. We located one of their pins at their SE corners that was on our west line and the inverse distance was 0.27 feet. That's pretty good to me. Every time I do a survey in an area I haven't been before I do a datasheet search and find an NGS monument near my site. I've also used them for elevation for topos and elevation certificates. I'm an NGS monument junkie.

Gavin,

What are your thoughts about the "half-life" of passive control?

I remember Larry Signani saying last year that after the recent NGS readjustment, you would be unwise to send older data to OPUS to get a "new" coordinates, as those coordinates, while in the readjusted coordinate system, might not jibe too well with the actual ground points, due to crustal motion, upheaval, subsidence, etc., and that if your raw GPS observations were more than a few months old, it would be much better to reobserve.

So, let's say I create a passive control network throughout greater Seattle. I'm guessing that you need to reobserve/readjust every time the NGS does a big readjustment, and meanwhile, the Earth is moving ... so, to keep that passive network "tight", seems like you would need to reobserve, or at least check in, every couple years.

I have found a handful of NGS marks that haven't been recovered since they were set in the 1936/1937 WPA survey era, but they have all been under so much canopy I have not been able to GPS them, and I have not had landowners' permission to chainsaw. I wish there was a way to submit a combination of GPS and total station measurements to put them in the next readjustment, but NGS seems to just want direct occupation with OPUS. I can see the quality control problems of accepting random mixed data, and I guess it would be un-economic to get NGS to write a procedure for mixed-method blue booking, but ...

I've found a few but never used them for anything other than a tie.