The Logic Behind Benchmarks

[+superpowerdave]

How does the USGS determine in what location they will place a mark? Is it up to the individual surveyor on what he thinks will be around for a while, hold position, something like that, or is it preplanned? Can a benchmark be placed anywhere, or are there guidelines for where they can be placed?

 

Just a few questions from the inexperienced with an appetite for knowledge.

[Z15]

This is a difficult question to answer here. You would almost have to work on a survey crew doing this type of work to understand it fully. The exact field locations to set a mark is up to the persons setting it..

 

But, yes there are standards and they vary by organization, purpose of survey etc etc. There are manuals many pages long to go into detail on how, when and where to set a mark.

 

There are several books you can look over, the 1st 3 links are to actual PDF publications and the last one to the page with them linked if you wan to download and read at your leisure...If you read thru these you will be more informed I am sure.

 

Control Leveling

Geodetic Bench Marks

Standards and Specifications for Geodetic Control Networks

NGS Publications

Edited January 31, 2005 by elcamino

[qwiffpop]

Caseyb, the NGS geocaching coordinator, introduced me to this forum.

 

I spent about 25 years in the field reconning the location for benchmarks and survey markers for the National Geodetic Survey. I was often the lucky guy who got to determine exactly where the mark was going to be placed, and in most cases I placed the thing myself. We had to space the marks out to cover a large area (create a statewide network i.e every 50 Kilometers).

When I was looking for a place to set a mark, I would look for a place the would not be disturbed. Rock outcropps were good because they were extremely stable and would hold an elevation well. In early days, benchmarks v(verticle control) were set along railroads because that was the way the country was growing, and it was easily accessible. There are a lot of verticle benchmarks set in old railroad stations, in the actual wall of the station. We no longer set marks along railroads, as it is dangerous and very difficult to gain access to them afterwords.

I set a lot of marks along highways, where surveyors can get to them. Parks, schools and places where construction wont be happening were also good places. We also look for sites where there are no trees or building that might block GPS signals. You will find a lot in headwalls and culverts.

I have set some marks in some odd locations. I have set a few on the roofs of buildings, and even one at the base of the golden gate bridge.

 

Hope you and all the other geocachers have fun finding these things. It really trips me out that you guys are looking for all these things I set over the past few decades. Enjoy.

[mloser]

Thanks! That actually helped a lot, not so much knowing that there were "rules" because there had to be rules, but how you guys thought it out and approached it logically.

To (hopefully) continue this discussion, a couple further questions:

 

How long did you spend on a mark? For example, if you were setting a mark by the road in a concrete monument, how long did you spend at that location, in setting and surveying the mark? Can you break down the process for us and how you went about it?

 

I assume you had to ask permission to set a mark on private land. Was it ever denied? What was your backup plan in that case?

 

I could go on (and on and on) but will let you off with just these few right now.

 

Thanks for your earlier response!

 

Matt

[Z15]

qwiffpop

 

Were you ever in upper Michigan? When?

 

It really trips me out that you guys are looking for all these things I set over the past few decades.

 

Someone has to check up on you.

Edited January 31, 2005 by elcamino

[+GEO*Trailblazer 1]

Thanks for the History, I am sure you will find alot of us have lots of questions.

Welcome gwiffpop.

 

On your recon did you try to use the Older mark that were there?

I have noticed that some are set on ,or in Older stones,cairns,ect.

Was this part of the work and or Historical documentation ?

[+Black Dog Trackers]

qwiffpop -

 

Take a trip down memory lane with us - visit some of the marks you set in the past and log them here!

 

If you have any amusing/interesting mark-setting stories that you or your associates experienced, please share them with us - we're fascinated with any stories related to surveying and survey monumentation!

[caseyb]

Go easy on the new guy.

 

Steve is a good friend of mine here at NGS. I asked him to get involved in the forums here at GC and we might be able to coax a few stories out of him He has hundreds.

FYI, here at NGS, and just about everywhere else, he goes by "The Mayor" not qwiffpop. Unfortunately both The Mayor and Mayor were already taken as screen names.

 

Glad to see you made it Mayor!

 

-Casey-

Edited January 31, 2005 by caseyb

[qwiffpop]

To all,

 

Once you select your location, in todays world you must call miss utilities and they schedule a time to come out and search for underground utilities so you wont break a watermain or cut through a fiber optic cable or whatever. If you are on someones farm or out in the boonies, dig the hole (45 min) depending on how hard the ground is i.e. rocks, ect. Mix the concrete (15 min). Stamp the survey disk and set it in the concrete (5 min). You should leave it alone for 24 hours so the concrete drys and does any settling., before you do the survey.

A GPS survey following NGS specs is a 5.5 hr long set up over the survey mark with a duel frequency survey-grade GPS antenna/reciever for 3 separate days. Post proccessing takes about 2 hrs.

Permission should be granted before hand by the propoerty owner and in some areas that can be trying. You have to be diplomatic and not scare them. Highway right-of-way is best as it is no problem. I have been turned down and then would move on to the next farm or would move out to the highway and look for a clear area for GPS.

I was once surveying on a private farm on an Coast and Geodetic survey marker , set in the 30's, and the owner came out with a shotgun and said get off his land. We did.

 

The Mayor

[ArtMan]

in todays world you must call miss utilities and they schedule a time to come out and search for underground utilities so you wont break a watermain or cut through a fiber optic cable or whatever.

Welcome to the club, Mayor!

 

When the utilities folks lay their infrastructure, do they check with NGS or other federal or local agencies if a benchmark could be affected?

 

The reason I ask is: This weekend I visited station GPS 142 (HV9131), which was placed by a private contractor for Fairfax County, Virginia, in 1991. The disk and its concrete mounting are displaced, as if nudged aside at some point below the surface. Spray-painted markings nearby indicate a fiberoptic run that is approximately directly beneath the station. Absent any other explanation, I am inclined the suspect that the concrete mounting of the station was pushed aside during the installation of the cable.

 

-ArtMan-

[qwiffpop]

They do not check with us (NGS) and if they moved that concrete it rendered the published position of that marker useless. That is illegal. It is important to look at the condition of the marker you have found for stuff just like you have mention. ...Good detail.....

 

Thanks

 

The Mayor

[qwiffpop]

to Geotrailblazerone....................The answer to your question is yes, we certainly would use the old existing station in that area, and infact it is mandatory we spend time searching for that station. Cairns can be built over the statiions at time of original setting or latter at another survey, it is hard to tell when, unless it was written in the description.

 

The mayor

[+rogbarn]

Welcome to The Mayor! I met him at the Lewis & Clark marker dedications in both St. Louis and Washington, MO. I showed him and several other state surveyors JC0585 which was originally set by the Missouri River Commission. The group decided that it was probably set in the early 1890s. Anyway, The Mayor does have stories to tell, so I also join in welcoming him to our groups.