z.cross
If you're reading real high up on the rod or if it's windy and the rod won't basically stand up by itself with a light touch to keep it from falling over or you're not using a level bubble on the rod, rocking it's a good idea, but on fairly level ground in good weather I don't think it's necessary for most leveling.
Jud - I never heard of that method but I can see the advantages. Everybody develops their own ways, I read the rod and say it out loud to myself, write it down then look at the rod again to make sure it says what I just wrote.
If you're too close to the rodman to see the foot mark, call out what you think you're reading and have the rodman move his finger to that point on the rod while you're reading it.
z.cross
Did you have a rod level? That would be better than rocking the rod, if the rod has a flat bottom shoe and you are on a flat surface like a stone step or curb top. Tilting the rod so it pivots on one edge of the shoe can raise the scale and give you an even lower reading than the correct one. This can happen also even if you are on a pointed object but the rod shoe isn't centered. It is a fine exercise in trigonometry to derive the formulas for the error.
I see that I took too long to compose this and am following two faster posters.
z.cross
We're just so excited not to be talking about junior monuments bending senior lines, we're falling all over ourselves to talk about something else.
I often liked to use the rear bumper of the truck as a portable turning point / benchmark. There was always an elevation nearby wherever I worked...;-)
Kris
You're right. I just logged back on and saw your remark.
Kris
Surveying picks the person, not the other way around.
That's a real good one Kris!
z.cross
> I'm not saying Zack didn't do this, but when I worked for my dad back in the 70's & 80's, he would get irritated if we didn't figure the HI's and TP elevations while the rodman was walking from point to point. That way, on a loop, you know how good or bad your closure is a few seconds after your last shot. Only problem with that is the instrumentman knows what he's supposed to see on the rod for that last shot.
Not if he isn't keeping the notes. Or if you are closing on a different BM and he doesn't know the posted elevation.
There are many ways to prohibit someone from "reading what they need to close".
If I don't know the IM well or have reason to mistrust, I will always set it up so that cannot be done to me.
Kris
> Surveying picks the person, not the other way around.
>
> That's a real good one Kris!
Interesting observation. Is that what happened to me? All I did was help build a workshop for a retired i-man. Then I built him a website and stumbled on POB. Then I some programs for a few surveyors. Next thing you all are telling me I should get into this. Next thing I know I'm being interviewed for an engineering/surveying firm. Next thing I know I'm their new rodman. A few months later I'm running the gun and DC.
I haven't touched a gun or rod in some time now but still find things all the time. A friend and me walked to a store yesterday and on our way back I came upon a local county benchmark. I remember telling when I was younger I always wanted a job outside and would never sit in an office. Well... I've done both now. What better job could I have to use my math and technical skills outdoors then surveying? Carperenting was close. Farmhanding was cool but no technical skills required. Logging was way too dangerous and no one in my family liked me doing that at all.
I reckon surveying picked me as well and I head to the field tomorrow if I got the call.
E.
z.cross
If you're too close to the rodman to see the foot mark, call out what you think you're reading and have the rodman move his finger to that point on the rod while you're reading it.
As a rookie, my Party Chief would insist that I have the Rodman “raise for red” even if I could see the foot mark above. He said it prevented one from calling out the wrong foot.
As a seasoned veteran I no longer do so, but agree that it is a good practice for the less experienced.
I did not see anyone mention this but we always have read the rod direct then inverted during a level run.
You take the entire rod length then when you take the first shot, and the invert they should add up to the overall length. Takes very little time and is the best way to avoid a blunder of reading the wrong foot marker.
Reading the wrong foot is probably one of the most common errors in leveling because if you are close to the rod and it's 4.95 then you probably see the 5'mark in the scope and it's VERY easy to write the reading down as 5.95.
Historic Note-When the rod give you the invert but forgets to turn it back over on the next point then this is also call a Beer Leg. Strangely enough, nearly any sort of foopah back in the days resulted in some sort of Beer Leg call.
As to not seeing the foot mark then I do both. I ask for a raise for red then I give the rodman my reading and ask him to put his finger on it as a check.
I love level loops as they are simple, pretty much error proof and you move along pretty fast with a good crew but like any work the fundamentals are important. Inverting the rod is just one of these for me.
> I did not see anyone mention this but we always have read the rod direct then inverted during a level run.
When I worked in Canada the level rods had metric on one side and imperial on the other. We would read both sides as a check.
Three Wire Leveling
Of course, one way to avoid the wrong foot reading is to use all three wires and take the average.
This also helps tell you how far out of balance the distance between your foresights and backsights are, in the event you need to assign weight to certain readings in your closure calcs.
I also often do what Jud does....in effect two level runs at the same time, using two rod men and setting up twice between each set of turns. It's a great blunder eliminator.
Three Wire Leveling
> I also often do what Jud does....in effect two level runs at the same time, using two rod men and setting up twice between each set of turns. It's a great blunder eliminator.
Once had to run levels from a BM on a railroad bridge to the top of a mountain for vertical mapping control. We used two levels and one rod, with two separate sets of notes.
Angelo
I always preferred doing three wire levels even for routine low order work, because it effectively eliminates blunders, I felt the slight increase in time was worth it in terms of not rerunning work.
As for double rodded-lines as described by Jud when we used them, we only used one setup per set of turns, that way any blunder would show up immediately in differing HI's.
This is my form for 3-wire level work. The right hand columns of the spreadsheet don't have to be in the field book.
Hmmm, looks like I responded to the wrong post, but it's close.
Bill, sorry to be overly nitpicky - however, z.cross is a college student and needs to know sig figs. your notes depict a greater precision on your mean values than could be obtained from the significant digits of your measurements.
3-wire
My final result should have an error estimate on it, which I didn't put on that spreadsheet, or else rounded back to its estimated precision. In this case since the closure was so small, I wanted to see what the calculated difference was without rounding even if it wasn't significant. So I confess you've got me there.
But not on the means. I've never been a believer in rounding intermediate results back to the precision of the inputs. Rounding is a form of random error and the fewer of those the better. Computer programs all carry lots more internal precision than the inputs or final answers, and that's great. Hand calculations can do the same.
The mean does have a little more precision than the individual readings, although not a lot more. If each reading has a std dev of 0.01 then the mean has std dev=0.006
Then with 8 values added or subtracted the std dev grows by sqrt(8)=2.8 so the final std dev would be 0.016. Assuming I read the rod with std dev 0.01 ft, didn't have any plumbing error, and the level was in adjustment.
As noted, this closure was found to be better than I had any right to expect, so I concluded the end point bench mark was in its original location.
I was checking to see if it had been disturbed, since the distance to the street, and height above the track were different from the NGS data sheet. And there was a RR signal building a foot away that wasn't mentioned on the data sheet, so it seemed likely they had graded down the bank to place the building and then said, "oh, that concrete post was over there".
In the end, I could explain away the discrepancies. I know railroad beds get built up over the decades. I found out the signal building was precast and placed with a crane so it was plausible they didn't disturb the post during construction. The street was asymmetrically widened, so one side matched up a block away and the other didn't.
