Jump to content
Sign in to follow this  
Followers 0
TUPPERHUNTER

Triangulation Stations

Recommended Posts

TUPPERHUNTER -

 

I don't know why you asked it, but you have an interesting question.

 

I tried the question on Fairfax County, Virginia near where I live. It has 1,353 benchmarks in it. I used DSWIN on that county somewhat like I explained here.

 

I selected the MONUMENTATION and ALL_REC_DATE fields in DSWIN. The MONUMENTATION code for a triangulation station disk is DS. The first REC_DATE is the monumentation date (which might be UNKnown).

 

In Fairfax County, the date of the most recently set triangulation station is 1984. There are 110 triangulation stations in the County and only 5 of them are mounted after 1970.

Share this post


Link to post
does any one know if triangulation stations are still being set?

NO

 

 

GPS has made Triangulation obsolete.

 

Triangulation of the Straits of Mackinaw connecting the lower and upper peninsulas of Michigan, in center of image

triangulation6.jpg

Edited by elcamino

Share this post


Link to post

The last triangulation project performed by NGS was in 1984 in Connecticut. Some surveys conducted by local governments continued to use this method until the late 80s. GPS has replaced that methodology for determining horizontal position.

Share this post


Link to post

DaveD -

 

Well this sorta begs the question - if no new triangulation stations are made now, are any of the existing ones still useful for something? If GPS is so powerful for establishing horizontal positions, maybe only the true benchmarks (vertical control) are the only stations still useful. Is this true?

 

Perhaps using a triangulation station and traversing locally from it is still more cost effective than establishing a position with GPS?

 

Is GPS ever professionally used for establishing elevation?

Share this post


Link to post

BTD.....good question and maybe one I can answer:

 

I am aware that Sunday River Ski Area in Bethel, Maine, invested in a Ground Based GPS station and together with WAAS have $5K-$10K back pack mounted survey units that they are using for precision layout of their new trails and facilities.

 

I guess this means that if you have the money and interest, GPS can replace Tri Stations. But this is a private organization dedicated to spending the money to make it happen. How long it will happen universally, I guess depends on how much the cost comes down and who is willing to afford it.

Share this post


Link to post

Probably the more common case is for some entity to contract a surveyor to establish a few accurate points. The surveyor would either:

 

1. Start from the nearest findable tri-station and survey along a few miles from it to the points, or

 

2. Haul out their fancy GPS unit to each point, sit in their truck while it works, and produce the results.

 

I imagine that #2 is cheaper.

Edited by Black Dog Trackers

Share this post


Link to post

:P Makes me wonder as to why we are hunting benchmarks other than to say we can follow directions? It's true that modern surveying is based entirely on GPS and few BMs are used anymore. When Coors Field was laid out in Denver, it was a big deal about home plate being located by GPS and the stadium built around it.

 

:( Recently, the City Utilities came out and needed one of my property corners so that they could plan the installation of a water pump. They just wanted to be sure they were not infringing on someone's property. Otherwise, the surveyor said he was a one-man crew and relied mainly on GPS.

 

:( Brings up another point: How can a BM have a scaled location and an adjusted elevation? If the scaled location is off by couple hundred feet, the elevation could change drastically.

 

:P Going back to the first sentence, I'd rather be looking for benchmarks that require following directions than walking up to a pile of rocks with a cache underneath. Guess it's the interpretation of what a surveyor saw when he mounted the disk 50-200 years ago. I find searching the libraries and museums about the history and maps very fascinating.

 

:P Am I alone?

Share this post


Link to post

No you are not alone.

 

There have really been some interesting questions brought out lately in the forums.

I see everyone is now starting to ask the questions I was referring to way back when.And am glad to see it.

 

There will always be questions to queries that will never be aswered and you can probably think for the reasons why.

 

If a Triangulation Station was in TWP 20N RNG.23W SECT.12 in the 1800's and in the 30's and 60's,it still should be in the same place today.

Correct????(Maybe)-not.

 

This goes back to the discussion on the PLSS.

It was mandated to be done a specific way,but is it really in all places?

And if not what does that mean?

 

So many .....?? that have been tossed around but never really answered.

 

If Triangulation Stations have been used for reference points for years how come now they have been outdated?

This is suppose to be the most accurate survey system of the time,and were referenced to in the initial work in laying out the GPS.

 

:( well i am rambling on again. :(

Share this post


Link to post

Well what I was asking about was the triangulation stations, intersections, and the other types of horizontal control stations.

 

The true benchmarks (elevation control), I am imagining are not being outdated by GPS, but I could be mistaken about that. They're also the ones that could use some better location than the old map-scaling.

 

I've seen the surveyors' stakes and stuff around PIDs and some of them are horizontal control, so they aren't so outdated. Odd that establishing them is outdated, but using them isn't.

Share this post


Link to post
Brings up another point: How can a BM have a scaled location and an adjusted elevation? If the scaled location is off by couple hundred feet, the elevation could change drastically.

 

That logic is not correct. The scaled position is to only help locate and plot the mark the mark and has no bearing on the elevation determination. The elevation was established by differential leveling by a survey team using specialized equipment and field methods. Here is a photo on one of my rod-man on a bridge project in 2002.

 

Notice the rod is bar-coded, level reads the bar code and makes it fool-proof or so they say. The data is then input in Levproc (software) and the elevations are computed and adjusted using least square adjustment program. Whereas the scaled elevation is a SWAG at the position.

 

There were about 5 NOS BM's, 1 HARN, 1 NOS GPS control mark all within 500 ft of this bridge with a NOAA water gage station also nearby. This is near mouth of river tributary to Lake Superior which is to the right in the photo about 1/4 mile.

RyanWithRod.jpg

 

NOAAgageTBM.jpg

Edited by elcamino

Share this post


Link to post
The scaled position is to only help locate and plot the mark the mark and has no bearing on the elevation determination. The elevation was established by differential leveling by a survey team using specialized equipment and field methods.

As an old-time surveryor, I knew that. Just wanted to make a point for laymen who may have wondered about it. Thanks for giving an explanation with photos.

We used many points for elevation when we ran a line and didn't care where they were. I wouldn't say we used "specialized equipment". Just a stadia level and stadia rod. We would traverse out a few miles then back by another route to tie back in then make adjustments. I don't recall what the figure was, but if we off by too much in closing the loop, we'd make another line to the new point.

46992c32-9672-442a-a087-a0efed99d66f.jpgThis is not me, but you can see the "specialized instrument" we used.

Share this post


Link to post
:laughing: Makes me wonder as to why we are hunting benchmarks other than to say we can follow directions? It's true that modern surveying is based entirely on GPS and few BMs are used anymore. When Coors Field was laid out in Denver, it was a big deal about home plate being located by GPS and the stadium built around it.

From what I understand to get full accuracy from GPS, it needs to be used in differential mode. That is one unit sits on a known point while another sits at the location to be determined. The data is later taken back and number-crunched. Existing stations such as triangulation stations are used for the "known" location.

 

GPS also eliminates or minimizes the need for triangles as a way of finding a location by traditional measurement methods. GPS has eliminated much of the need for NEW triangulation stations, but it still values the existing ones.

Share this post


Link to post

Triangulation, trilateration, traverse, and GPS are all just methods to establish horizontal control. GPS is the main method today.

 

Not exact textbook definitions, but simply put. Triangulation was mostly measured angles with a few measured distances. Trilateration was mostly measured distances with a few measured angles. Traverse is a series of measured distances with measured angles at each angle point. Triangulation and trilateration are still used by surveyors somewhat, but traverse is alive and well and used in areas where GPS will not work like under tree canopy or places like this…

http://www.leica-geosystems.com/media/new/...gotthard_en.pdf

Share this post


Link to post
Here's a picture of a gaging station disk I stumbled across:

 

gagingstation.jpg

We found one exactly like this disk, also with the circle in the center of the disk, and words 'GAGING STATION' around it, and 'REFERENCE MARK' below it. It has a designation GAGING STA in the database.

It was positioned precisely as described in the datasheet, but since it was labelled an RM, I assumed that it was not what we were looking for. Although most of the RM disks have arrows on the disks, rather than circles.

d3bfef37-90eb-40ee-bb24-335e1e79dbe5.jpg

I tentatively logged it as a DNF, but my trip partner thought it was a find. Could the forum gurus please help us to decide if it was "it"? And maybe append jeff35080's image to DustyJacket's library?

Share this post


Link to post

USGS frequently set several disks and chiseled marks at their gaging stations. If it is in the right part of the structure and the distances and directions to nearby objects match the description you found the mark. Just last week I helped another surveyor with a disk at a gage where there were three disks and I think some chiseled marks.

Share this post


Link to post
If it is in the right part of the structure and the distances and directions to nearby objects match the description you found the mark. Just last week I helped another surveyor with a disk at a gage where there were three disks ...

You mean three disks, *all* labelled as RMs? (It sort of makes sense for me because they probably need durable vertical reference points for the gage itself ... it also explains the absence of the usual RM arrows)

Or there should be some *main* monumented mark, in turn referenced by a separate set of RMs?

With respect to description of LO0303, the problem is that there is no momumenting report by USGS. There is a later-date report by National Geodetic Survey, which surveyed this highway in the 60s, and the description is very terse and doesn't mention any other marks. The rest of the BMs along the road were monumented by them, and they were benchmark disks. This one has DD = SURVEY DISK for a marker type. Can anybody markwell me to a complete list of marker types? In any case I doubt if survey disk is the right marker type for gaging station marks ... or is it?

Share this post


Link to post

what i ment about that is if the usgs benchmarks are in the ngs database or if you have to go the usgs site and somehow find the data sheets. af any one can help in reference to usgs 04266500.

Share this post


Link to post

OK, it occured to me that my "GAGING STA" must be be just one out of a long list of USGS gaging station marks co-opted into NGS database. An indeed, a search for designation GAGING returns 100 entries.

this one for example is described as "A UNITED STATES GEOLOGICAL SURVEY STANDARD GAGING-STATION DISK" and has DD = SURVEY DISK for marker type, but this one is described as a standart-issue USGS gaging station reference mark. Some other are described as benchmak disks, or as DO = NOT SPECIFIED OR SEE DESCRIPTION (with descriptions referrring to A STANDARD U.S. GEOLOGICAL SURVEY GAGING STATION DISK. GC1246 is described as A UNITED STATES GEOLOGICAL SURVEY STANDARD REFERENCE-MARK DISK, but marker is SURVEY DISK:

31653_100.jpg

Same discrepancy between description and marker fields holds for OE1107

12700_100.jpg

SY0162 is a less clear case because of short description, but the finders' picture is a familiar RM. Similar situation for GZ2135.

Hmm, maybe I should change my log to find.

Share this post


Link to post

It could be that, in Gaging Station vernacular, the term 'reference mark' has a different meaning than it does with vertical or horizontal control disks. It may mean that it is a positional reference for the gaging station.

 

I'd count these as finds.

Share this post


Link to post

I have been to several USGS gaging stations in my area. All are on streams tributary to Lake Superior. None have any survey disks, the bridges nearby on roads have old chiseled marks from the USGS Surveys of the past. There is a gaging station near me, about 1 mile on a rural gravel road. The survey mark for that one was on another small bridge close by and the bridge is now gone along with the mark.

 

A USGS water resources office used the second floor of our office building in Escanaba, MI. They had several techs that roamed all over the Lake Superior region monitoring and observations on the streams.

Edited by elcamino

Share this post


Link to post

The Data resulting from Geodetic Triangulation are primaraly for Horizontal control data which are expressed in the form of Geodetic longitudes and latitudes(or equivalent coordinate value)of definite established points and include distances and azimuths for all lines observed.

 

These points are normally marked by bronze discs(most frequently set in concrete monuments)but also include many prominent objects,such as water towers,church spires,and radio towers.

Descriptions and geographic position of these established points are published for public distribution.

 

So on the disc, it is the reference disc,mark of marks the actual gaging station is the station, usually has a gage on a level vertical pole, painted like a rodmans pole in alternate colors,you can observe the water level at anytime from the gaging station.(their function).

 

On adjustments of marks vertical or horizontal,a movement in any way will degrade the accuracy of the original observation.Azimuths,bearings angles and backsights.

 

If I adjust coordinates in my mapping program the elevation is also changed as we are now at a new location with a different long-lat and elevation.

 

So now,a new set of calculations are created,observed and adjusted.........

 

Didn't this happen in 2000

SRTM: Space Radar Topography Mission.

Space Radar Topography Mission

 

SRTM MISSOURI

Share this post


Link to post

Here is a sample description of a gaging station with multiple disks. They are vertical (elevation) references only. The water resources guys at USGS are a little brief in their descriptions. I wish that they would go into more details when they set multiple unstamped disks at a gage.

 

http://img.Groundspeak.com/user/1e40cfbf-9...bcd0a00ddd0.jpg

 

http://img.Groundspeak.com/user/91b30514-f...f88ba35ee3c.jpg

Share this post


Link to post

So where exactly do you get the usgs data sheets? i tried looking in the ngs data base but no benchmarks at the station cords.

Share this post


Link to post

We have paper copies where I work. I don't think that they are on the web. I have looked too.

 

The USGS Water Resources Division office in your state might be the place to start.

http://water.usgs.gov/local_offices.html

 

Or

 

http://ask.usgs.gov/

 

I doubt that very many have been tied in by NGS. If they were working in the area they might tie in the USGS marks and publish them instead of setting their own disk on the structure.

Share this post


Link to post

Here is a nice gage page with 7 reference marks (to the gage). The gage has lat-long coordinates and the reference marks are vertical controls relative to the gage with vertical distances in feet with 3 decimal place precision (about 1/3 of a millimeter!).

 

Starting with this URL, you can get to a list/map of 50 states to find other gages. The few other ones I looked at had no reference marks. I saw interesting graphs of our last couple rainstorms in local gages, however. :P

Share this post


Link to post
Here

Starting with this URL, you can get to a list/map of 50 states to find other gages.

Couldn't figure out where to go from this page. And googling 'Gaging station description" returned only 29 pages from usgs.gov, almost all of them are individual station descriptions posted on the same md.water.usgs.gov site.

I found some sort of data for "my" station at waterdata.usgs.gov through their station selector, but it is not a detailed description.

Share this post


Link to post

Here is the Utah state USGS site. The USGS seems to have 2 types of urls for gage data; one that starts with a state code like this one and the other that starts with "waterdata". In either case, the Maryland sites seem more detailed for our perspective.

 

I guess different projects have different criteria of what they enter into their websites.

Share this post


Link to post
The gage has lat-long coordinates and the reference marks are vertical controls relative to the gage with vertical distances in feet with 3 decimal place precision (about 1/3 of a millimeter!).

 

BDT, your reference to the USGS Gage Station does show that they had accurate levels between their points at the station, but if you notice the Datum is:

Datum of Gage - 8 feet (from U.S.G.S. topographic maps).
Not very accurate. This is why most gaging stations are not listed unless NGS ran levels through them.

 

CallawayMT

Share this post


Link to post

I was able to email my state department of the usgs and they where able to mail me a decription of the station that includes all of the marks around it!

Share this post


Link to post

If you get one of the descriptions it will tell you all of the marks around it. also for you tech inclined it tells you all of the electronics in the building, what it uses for flotes, and the controls for the flow, and some other odds and ends.

Share this post


Link to post

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
Sign in to follow this  
Followers 0

×
×
  • Create New...