Say you are running elevations using a total station. Does anyone keep track of the distances from the gun to each TBM? Say you are carrying an elevation two miles down a straight county road.
Yes, I do, it's important to balance the shots when trig. leveling.
:coffee:
Yes. I do.
Yes. Agree with RFB & Deral.
I want to avoid being bitten by earth curvature and refraction.
"....running elevations using a total station...."
Does anyone do this without a data collector?
I did for many years. Just your standard rite-in-the-rain book. It's what we had back then.
Always carried elevations whether on a boundary survey or a route survey.
dp
why would you not use a level?
Butch
Why would you not use trig levels.
I agree, for a short run, I'd use a auto level. For long runs, I use trig levels.
Butch
If trig levels, then shot from both ends, D&R, I hope.
Bill
It kinda has to be to be true trig levels. I'm not talking about a trig traverse.
Rick
I beleive Jesse K once said on here that it is not necessay to balance the lengths of legs when trig leveling.
You know how when running a strictly horiz trav, if your b/s is 0.02' off (left or right), you will push out that error and it will expand the farther you run.
But when trig leveling, the DC uses the b/s BM to calc it's HI. Then all vert measurements are from the zenith, or whatever. The gun does not project a tilted horiz plane to measure it's vert angles, so any error is not magnified.
why would you not use a level?
If you are covering steep ground, it is quicker with trig.
Steve's right
I just looked it up HERE.
Now I want to change my answer to: Yes, you need to keep track of the total distance traveled to ensure the run meets MTS.
Allowable Error = .05'*sqrt(Distance in miles)
but of course, vert< etc...
Steve Adams
You remember correctly' I have a .pdf of 2 of Jesse's presentations on trig leveling. I found the following:
"There is no requirement for balanced sight lengths and differences in elevation between backsight and foresight in one setup of 20 meters or more are not uncommon on steep terrain" in a presentation called:
Electronic Total Stations Are Levels Too
Precise Trigonometric Leveling Using
Modern Total Station Instruments
By Jesse Kozlowski, PLS
Trimble Navigation Ltd
Overview
Sorry, I can't find a bookmark for it now, I may have just copied it without a link.
Edit, It looks like Rick is quicker than i am.
Trig leveling pdf
This PDF doesn't indicate that its form of trig leveling can be made immune to earth curvature effects, so that is a reason for keeping BS and FS distances similar.
> why would you not use a level?
>
>
> If you are covering steep ground, it is quicker with trig.
I agree, usually the terrain dictates the need for trig leveling. Depending on accuracy needed I suppose, it seems otherwise one is using it to carry longer shots and get done quicker?
Bill93
I have a different one, it's more like a written report, it also contains the results of a test run by NGS in VA. It's more in depth than the slide presentation.
I have the one you linked to above, also.
I used this method effectively in the late '90's when I had a project that involved setting BM's at all the water tanks in our distribution system.
If you're interested in it, I can e-mail it to you.
Another paper
There's also this magazine article by J.K. which has more discussion than the slide show. It mentions that the curvature needs to be applied.
In my first post above I was thinking of the "trig leveling" discussed in older textbooks where you set up near each end and observe vertical angles both ways. The average of those measurements DOES cancel out curvature and refraction. There can be a problem if refraction changes while you are getting to the other end, so they suggest simultaneous reciprocal measurements under those conditions.
Bill
The PDF i have is a draft of the magazine article, the only difference I see is the NGS test results.