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Calibration Baselines...how many go regularly?

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John Hamilton
(@john-hamilton)
1,000+ posts Member

We go to a CBL once a year, in the spring. More recently it has been a requirement in our scope of work, but we had been going annually before that. Last year I went to the NGS Corbin baseline (5 hours away) because I had my doubts about one that we use in Ohio that is about 3 hours away, as it is located at the base of a large earth dam. It is nice to use because they keep it mowed and it consists of pillars (no tripods, no centering errors). This year we are going to one that is 2 hours away at a small airport. There is one closer but I believe someone told me it is no longer intact (missing stations).

I use calibrat.exe (dos program form NGS) to process the data (i.e. to determine the constant offset and ppm). 

I know a few surveyors who never go, others that do somewhat regularly.

I think in some states it might be a requirement in the standards and specifications? 

 

 

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Topic starter Posted : May 2, 2022 12:14 pm
Rover83
(@rover83)
1,000+ posts Member

I haven't been to a CBL in a long, long time. There are a couple around here that are supposedly in good condition, all at airports where access can be a pain.

Our instruments typically get their EDMs calibrated during their annual service. A full service shop should have an "infinity" electronic baseline setup that can determine the values in the shop.

I would probably want to verify those values if I were doing as much deformation work as @john-hamilton, but our high-precision work is pretty minimal these days.

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Posted : May 2, 2022 1:18 pm
not my real name
(@not-my-real-name)
500+ posts Member

Two of the calibration base lines in my state that are close enough are now inaccessible. One, at an airport has the first and last point useless because of an improvement project. They made a bunker that obscures the end point and a hole where the first point is. Clever.

The second is in the median of a highway and due to the fact that everyone with a cellular phone uses it to report some kind of terrorist activities when surveyors attempt to use it, has become useless. I have been told, with enough cones to delineate the 1300 meters of base line and a State Police detail, I can work there. Can you say budget buster?

With those two out of the picture, I would say it would take most of the day just to get to the others, and being a stranger in town, I don't know if I would want to risk it. 

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Posted : May 2, 2022 1:41 pm
JPH liked

Chris Bouffard
(@chris-bouffard)
500+ posts Member

I have two CBLs in the southern half of the state.  Both are not worth going to, on is at an airport with limited access and the other is too close to the road to safely park.

We have six Leica guns in service and a spare.  All the guns, including the spare are sent in for cleaning and calibration once a year, on a rotating schedule and we get a yearly calibration certificate for each to keep in our files.

The state requires it, but, they never check on it.  It's the same with continuing education, it's required, I comply but nobody, since I was licensed in 1993 has ever asked to see my CEU certificates.

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Posted : May 2, 2022 2:09 pm
John Hamilton
(@john-hamilton)
1,000+ posts Member

I understand about the yearly dealer clean/calibrate. Probably what most do nowadays. I wonder how accurate their method is. I believe my dealer told me one time that they shoot an actual line across the river to a prism mounted on a building on the other side. But of course there is always the issue of buildings moving/expanding/contracting/settling, and what did they use to establish the line in the first place? 

When I went on a tour of the Trimble factory in Sweden years ago (former Geodimeter factory) they had a window that they opened and shot to a distant prism on a building, and they said that they tested every S6 that way before they shipped. 

I take one instrument/prism combo to the CBL, and then bring it back to my office and use it to measure between the two pillars that I have, which are about 135 meters apart, and then check other instruments/prisms against that. 

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Topic starter Posted : May 2, 2022 2:32 pm
GeeOddMike
(@geeoddmike)
1,000+ posts Member

In response to Mr Hamilton’s post, I took a look at the NGS CBL page: https://www.ngs.noaa.gov/CBLINES/calibration.shtml

I had not realized that new policies and participation procedure documents had been implemented in 2021. Also there is a Windoze 32-bit program (Calibrate) available for reductions. 

The page above has links to the various elements of the program as well as the related technical memoranda (NOS NGS TM 8 and 10).

NGS will cooperatively establish, verify or remeasure a Calibration Base Line (CBL). In the case of a new CBL the partner is responsible for finding a suitable site, set monuments, run levels between monuments, clear lines-of-sight and provide a support person for the actual measurements.

I did not see mention of a training class which was the case in the late 1990s. I took the class overseen by the late Charlie Glover. I worked with the state land surveying society to set one CBL and remeasure another CBL.  NGS provided the specialized and calibrated equipment. While I have not noted much mention of the use of steel tapes, there are procedures allowing a 100 foot monument to be established as part of a CBL.

In closing, I once attended a state society CBL “event” where attendees could check their EDMI. Unfortunately most chose to measure only one or two segments and if they agreed within their comfort level thought that was enough.

 

 

 

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Posted : May 2, 2022 3:31 pm

Jitterboogie
(@jitterboogie)
1,000+ posts Supporter

I ran the KELIM CBL once with our new at the time  0.5" S9 HP we used for our precise structure/monitoring work we did,and yeah I'm a dork, I found that pretty cool. 😎.

It's always to see if YOU can perform at the instrument's ability.

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Posted : May 2, 2022 4:03 pm
Norman Oklahoma
(@norman-oklahoma)
5,000+ posts Member

I don't go as often as I should, especially as there are 3 of them in the Portland Metro area.  But I do go more than anybody I know.  Which is to say that I have actually been to it.  On one occasion I went to the Hillsboro base and found that a highway sign had been erected smack in the middle of it 6-8 months prior. It took another 6 months to get the sign moved. So I know for a fact that nobody had used it for that period of time. 

I once visited one north of Tulsa, OK. It was overgrown with 6 inch trees. It takes about 20 years for trees to get to be 6" diameter in OK. 

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Posted : May 2, 2022 4:48 pm
Dave Lindell
(@dave-lindell)
1,000+ posts Supporter

Prelude: I think most baselines that have a monument to check steel tapes have it set just under 100.000 feet so that every tape can be checked, especially ones that are made just shy of 100.000 feet, say, 99.975 feet between "0" and "100" on the tape.

A surveyor I met decades ago took his steel tapes to a baseline and thought otherwise: that the distance between 0+00 and 1+00 was exactly 100.000 feet.  He used his "calibrated" tapes to do dozens of surveys before he was corrected.  To his credit he filed a Record of Survey to cover every erroneous survey.

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Posted : May 2, 2022 5:35 pm

RobertUSA
(@robertusa)
200+ posts Member

It’s interesting that there’s calibration baselines for checking total station distances, while many surveyors rely heavily on RTK (VRS/RTN even which has more error than local base RTK), where with RTK you can measure two points , then measure those points an hour later and observe a different distance between them compared to the first observation. Basically RTK (VRS is network RTK and has more error than local base RTK) is a variable distance measuring device. 🤔

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Posted : May 2, 2022 5:57 pm
John Putnam
(@john-putnam)
1,000+ posts Member

@norman-oklahoma 

I think the Hillsboro CBL could use some tender loving care.  When I last visited it (in 2020) I noticed that one of the points had been hit by a mower or something.  It is almost impossible to distinguish the punch mark on the monument.  I like the idea of have monument pedestals at the points.  I wonder if ODOT would let us place them that close to Hwy 26? 

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Posted : May 2, 2022 6:32 pm
Tim V. PLS
(@tim-v-pls)
200+ posts Member

I drive by one nearly every weekday, but haven't set up on it in years. I did park my work truck next to it a couple of times to let my dog run through the adjacent fields. 🙂

To me, centering error and bubble adjustment are way more important.

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Posted : May 2, 2022 6:36 pm

John Putnam
(@john-putnam)
1,000+ posts Member

@robertusa 

Error's detected on a CBL are systematic and can be accounted for while those associated with GNSS (post processed and real-time) are random.

Of course this assumes a stable setup for both.

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Posted : May 2, 2022 6:37 pm
OleManRiver
(@olemanriver)
100+ posts Member

I have been discussing the baseless with my boss man. They too send instruments in for clean and calibration.  But When I was out west in late 90’s we took every total station out to the baselines like clock work . I became very efficient at it. Doing 7 total stations twice a year as soon as they returned from clean and calibration was something that became a part of my routine. Now we rented a high end wild 1/2 “ total station for the Henderson mine project. Took it to two different baselines because it was systematically reading the distance incorrectly. Then they finally fixed it at the shop. So its good to let the crews learn what is and how to prove the federally mandated weights and measure come from. If I were licensed it would not matter if my state requires it or not I would still take a day to run to a baseline and mentor the younger generation into learning this. Plus it really doesn’t take long but can make for a good day of one on one with an upcoming potential license person for the LS PLS to have a way to accomplish something and even get a little time with employees outside the daily grind. I remember jamming to the radio from the old f150 cracking jokes with the Party Chief and seeing who could set up the targets and instruments the fastest and double checking each other. Did steel tapes as well. That baseline holds more weight in my opinion than a manufacturer. Hopefully my boss will find time to head up and have a half day to let us run through one .  

 

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Posted : May 2, 2022 7:20 pm
Mark Mayer
(@mark-mayer)
1,000+ posts Member
Posted by: @john-putnam

I like the idea of have monument pedestals at the points.  I wonder if ODOT would let us place them that close to Hwy 26? 

No way. Imagine the traffic hazard. Now, perhaps the Aurora or Vancouver Lake baselines.....

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Posted : May 2, 2022 8:25 pm

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