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I've heard that called double-rod leveling. It's just a check to see if you get the same elevation difference because there would be 2 backsights and 2 foresights per setup.
Another method, and I'm not sure what this is called, is when each setup is it's own tiny loop. You take backsight reading then foresight reading, then kick a leg (reset the level in relatively the same spot with new HI) then take the same backsight and foresight readings again before moving on. Then you have a double check on the elevation differential between point 1 and 2. What's the term for this? Maybe this one is double rod?
I'm not buying a digital level and bar-code rod to run one loop every year or two. It's not just about 'which is better'...
I'm curious if anyone has ever used a yard rod for 3 wire. Its a 9' rod divided into yards and hundredths of a yard. You estimate the 3 wire readings to the thousandth of a yard, make sure this difference between the top hair and middle hair, and the bottom hair and middle hair are within .002yd, then instead of averaging the 3 readings you simply add them together to get you answer in feet. I used this for dam monitoring which was set up in the '20s. the same rod was used twice a year..
never seen one since.
Double Simultaneous
The method you mention sounds a lot like "double simultaneous" leveling.
Using a Wild N-3 and dual scale invar rods offset by 301.555 meters, we would read the backsight stadia, the backsight high scale, turn and read the foresight highscale and then the foresight stadia.
After tapping the instrument and releveling we would read the foresight lowscale and then the backsight lowscale.
The difference of the high scale readings and the difference of the lowscale readings had to agree within 0.25mm or the entire set of readings was done over.
And the distance to the rods couldn't be unbalanced by more than 2 meters. No readings were allowed below 0.5 meters.
And if that wasn't enough, we ran it back again.
Double Simultaneous
Yea....that's the method I was talking about. I think you had the order of shots a little different than what I said, but it's the same measurement. That was for really high precision stuff. I don't think I've actually used it in practice many times.
> I've heard that called double-rod leveling. It's just a check to see if you get the same elevation difference because there would be 2 backsights and 2 foresights per setup.
>
> Another method, and I'm not sure what this is called, is when each setup is it's own tiny loop. You take backsight reading then foresight reading, then kick a leg (reset the level in relatively the same spot with new HI) then take the same backsight and foresight readings again before moving on. Then you have a double check on the elevation differential between point 1 and 2. What's the term for this? Maybe this one is double rod?
Double rodded levels lines that I was taught to run were using two rods, i.e., BS #1 & FS #1 - Move to next level setup - FS #1 rod becomes BS #2 rod and BS #1 rod becomes FS #2 rod, etc. in the same sequence throughout the level run.
> I'm not buying a digital level and bar-code rod to run one loop every year or two. It's not just about 'which is better'...
I did, but it allows me to take on jobs I wouldn't otherwise be able to get. Not many outfits around here have an invar barcode rod...
I'm certainly not going to try to dissuade anyone who wants to run 3-wire levels from doing so, though it's worth noting that if you're using a conventional engineering-grade level and rod you're not going to meet anything better than Third Order accuracy specs no matter what you do. I doubt that a 3-wire loop is going to offer any practical increase in accuracy over a 1-wire loop run with care. And then there's the time lost to the "remembering curve," the need to re-learn how to do something that's only done once every year or two. 3-wire isn't for the faint of heart unless you do it regularly, or have done so much of it that it's like pacing in your sleep.
My original comment about not bothering to learn 3-wire was directed at the OP, who seems to be new to the game and needs to learn a whole lot of things that would be more useful than running 3-wire levels. But if that's really what he wants to learn, I think he should go for it!
I've never done 3-wire leveling in practice, but when I was back in college (over 20 years ago) we did several exercises with the yard rod.
The thing I remember the most from this method is to find the top-middle and compare it to middle-bottom. If they didn't match (I believe the tolerance was 0.003) then you read the rod again. I believe this not only checked that you didn't bust a reading, but it also would clue you in that the rod may not have been plumb.
In any case, it is a very reliable method for accurately running level loops. We have a digital rod with bar code here at the office that we typically use. But if the battery were dead, the tried and true 3-wire method would be the standard for me.
Only thing I ever do is run the level rod never did anything with the auto level
My first day was April 12 of this year. My company uses 3 wire. We don't use digital level. That why I am wanting to get it learned.
Some of these comments make me feel old. I've probably run several hundred miles of 3 wire. Double the center reading. Add the top and bottom. If the sum of the top and bottom are 0.01 more than the center doubled add 0.003 to the center. If the sum of the top and bottom are 0.01 less than the center doubled subtract 0.003 from the center. This is the pre-calculator method. Of course an equal sum to the middle doubled is flat. Anything else is a bust.
I think Jim F summed it up good. Not to long ago I worked for a city who had a pretty extensive network of BM's that were all run with 3 wire. Then the data plugged into Starnet and it majically adjusted things closer than the eye can see. But it does compensate for distance, temperature, and all that stuff to get the published elevations, and you could rely on them.
I tried to get them to buy a digital level, but they weren't going in that thar' newfangled direction. Same logic about a robot.
"Elementary Surveying" by Wolf, Ghilani;-)
:good:
> I am woundering exactly how to run a 3 wire. My party chief has explained to to me but he is horrible at teaching . Trying to learn everything I can now make life easyer later.
I have not read through all of the replies, but I did see a comment or two about learning antiquated methods, eg 3-wire levels.
My advise to everyone would be to learn all one can about the basics of surveying and the older methods. One never knows when this knowledge may serve you well. Become a student of your chosen career.
Having been in this profession for 37 years, I have had to opportunity to encounter those whom I refer to as "digital dummies". Should the data collector, computer or the total station break, these "digital dummies" have no idea how to proceed. Even the use of a compass and cloth tape can save valuable time and effort should modern equipment fail.
:good:
> I'm not buying a digital level and bar-code rod to run one loop every year or two. It's not just about 'which is better'...
Digital levels are surprisingly inexpensive, simple to operate, increase the speed at which levelling can be run and processed, and eliminate transcription errors. If you had one you would probably be more inclined to run levels.
I'm not saying anything, I'm just sayin'.
> I'm curious if anyone has ever used a yard rod for 3 wire. Its a 9' rod divided into yards and hundredths of a yard. You estimate the 3 wire readings to the thousandth of a yard, make sure this difference between the top hair and middle hair, and the bottom hair and middle hair are within .002yd, then instead of averaging the 3 readings you simply add them together to get you answer in feet. I used this for dam monitoring which was set up in the '20s. the same rod was used twice a year..
> never seen one since.
I was wondering if anyone was familiar with the yard rod.
That with a rod bubble and a micrometer level or a rod target used to be the way to get real 1st and 2nd order work.
B-)
> > I am woundering exactly how to run a 3 wire. My party chief has explained to to me but he is horrible at teaching . Trying to learn everything I can now make life easyer later.
>
> I have not read through all of the replies, but I did see a comment or two about learning antiquated methods, eg 3-wire levels.
>
> My advise to everyone would be to learn all one can about the basics of surveying and the older methods. One never knows when this knowledge may serve you well. Become a student of your chosen career.
>
> Having been in this profession for 37 years, I have had to opportunity to encounter those whom I refer to as "digital dummies". Should the data collector, computer or the total station break, these "digital dummies" have no idea how to proceed. Even the use of a compass and cloth tape can save valuable time and effort should modern equipment fail.
:good:
B-)
BTDT,
Been surveying since 1967. It is amazing how much the equipment has changed.
I know of one licensed surveyor that if you took his pre-programmed calculator and his computor, he couldn't calculate a right triangle, much less an obtuse one.
