Hi guys
I've got a topo to do next week. The nearest benchmark is about half a mile away (I reckon about 6 setups to get to it and another 6 to get back) through a windy (twisty) country lane.
Is this too far (too many setups) to level into the site?
Cheers, Andrew
No.
No, it's not too far.?ÿ
Level runs like that can be done pretty quickly, and sometimes are the best method, over other more modern ones.
How far would I go?
As far as I had to! I'd make a hundred turns if that was what I had to do, 12 turns is laughable. What's the problem?
No. The distance is inconsequential. Aside from that, you should always check into a second benchmark.
You need to run that distance twice to close the level loop. 1/2 mile is nothing. We've run level 10 miles, back and forth. A digital level well suited for long runs.
No, that's about right.?ÿ Keep site distances even per setup (bs fs equal) and limited distance.?ÿ Assuming they were all the same (which they wont be I know) you would be sighting 220 ft each which is reasonable.?ÿ I would be more worried about having too few setups (too long of sight distance or unequal bs fs to gain ground more quickly). Of course double the above to get the loop.
I'd need more information to answer the question.?ÿ What standard are you required to meet??ÿ (Are there client requirements or state minimum standards involved?)?ÿ Does the topo have to be on a published datum at all??ÿ (If it's just for onsite drainage, datum may not matter.)?ÿ If it has to be referenced to a publish datum, how accurate does it need to be??ÿ (Will an RTN or OPUS elevation suffice?)?ÿ Do you have a 2-person crew available? (Solo operators tend to avoid leveling.)
All good comments so far.?ÿ You may also want to consider trig levels, which is not a trig baseline measuring down to your station.?ÿ Look here:
https://surveyorconnect.com/community/surveying-geomatics/trig-leveling-procedures/
Ken
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NO, it is not too far.
We have run miles to reach sites.
Not that many BMs in this county.
We often use the TS as a level and also trig leveling.
The nearest benchmark is about half a mile away
You hit the jackpot to have one so close.
I know of level lines in the NGS data base where there isn't a reliable bench mark remaining for 15 miles.
I've run 2-1/2 miles one direction. Always a closed loop. Accuracy? Less than a tenth. As I recall, it closed by 0.07' Record to 0.001' via interpolation.
Rock the rod. Focus it carefully.
We did the 2-1/2 mile run (5 mile loop) in 2 days. We had some average of 300 to 400 feet per shot. That's a little far... But with young and good eyes, and a good, and properly indexed level, it worked. Start early, before heat shimmer gets going. Quit or reduce shot distance, as heat shimmer starts.
Cool temps helps.
N
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As others have said a 12 turn loop is just enough to get warmed up.?ÿ It's not a long loop at all. And there is no better way, in terms of accuracy and simplicity, to transfer elevations.?ÿ?ÿ
Nate's suggestion of rocking the rod is a good one for old hands - like Nate and myself. But I sense from your question that you haven't done a lot of levelling. Reading the rod correctly is tough enough when the numbers aren't moving. So I suggest you get and use a rod level.?ÿ Read the rod, write it down, read what you've written, and check the rod. Move on.
Every couple of blocks of your outbound leg (2 or 3 turns) make your TP something permanent. I like to use something on the top of fire hydrants, which are always at about that spacing in the city. But just anything solid will do. Drop a nail (or even a paint spot) if you have to. Then turn back through them on your return leg. If you've bollixed up a measurement that will isolate your error. You won't have to redo the whole loop.?ÿ
That's a great use for a fire hydrant, short term.?ÿ But be very cautious about using that elevation for it later.
Bill above is so right about fire plugs. They are not stable.
Water temperature varies. Water lines shrink, and contract. Pressures change.
City moves them.
Quite simply, they are part of a "high activity hydraulic world, full of kinetic activity, beyond your control".
Autos hit them, and they get twisted around, by forces beyond our control.
Sometimes, they are stable, and shift little, for years, but go up and down a little, morning, and night. Winter, and summer.
This can introduce a few hundredths. A re installed one via city water dpmt. can look the same, but be changed 1/2 a foot.
They are just that way.
N
What, no mention of the need for a collimation check before starting? See:?ÿftp://ftp.ngs.noaa.gov/pub/locus/3%20Collimation%20Check%20and%20Field%20Notes%20v1.ppt ?ÿIf your level is not in adjustment you will have problems. Depending on your terrain it could be hard to achieve balanced sightings.
I always found leveling to be tedious and monotonous. Doing it correctly requires painstaking attention to detail. At high levels of precision specialized equipment and modeling of observables are required.
It is the most precise method of height determination at the distance the original poster mentioned. I agree with previous posters that work should be performed to achieve a standard.?ÿAlso, as previously posted, determining a height with respect to only one monument assumes that values associated with it are accurate. Gross changes to the physical monument might be detectable; damage to a monument a decade or more after it occurred may not. Check leveling between at least two monuments at each end of the level line is always recommended.
As Bill93 mentions, the decimated national network often does not provide easy or convenient attachment to the NAVD88 network.
In closing, I hope you have a plan to perform the work safely. Winding country roads are great for taking the sports car out. Traffic control measures must be considered. Some areas require permits to work along the roadway.
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Three to four miles several times. ?ÿBe careful. ?ÿRun out and back with side checks along the way for bust control.
the single best investment I made as part owner of a survey company was a Sokkia SDL 30 digital level
Hi guys
Thanks for the answers. I work solo and haven't done a great deal of leveling to date. Mostly my clients have been happy with a local site benchmark, but these days they are more and more asking for levels related to the national UK datum so the building and site can be 3 d modeled with surrounding landscape levels. I've managed to do this so far by getting a level off a manhole with a known elevation (and an additional 2 manholes for checks). But some sites aren't on main drains!
As I work solo levelling is a problem unless I drag someone out for the day which I'm reluctant to do.?ÿ What are my other options? The level transfer doesn't need to be massively accurate as its for topo work.?ÿ Within an inch should be fine.
Is this a good excuse to get GPS? It would mean I could do boundary work too.
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We used to run levels 20 miles and think nothing of it. We now use GPS to transfer heights into topo sites. Come on guys and gals. Time to confess.?ÿ
Actually we prefer using GPS to leveling for a number of reasons.?ÿ
1. Time
2. Done correctly it allows you to investigate the area rather than one or two local benchmarks.?ÿ
3. What is the best representation of datum when the source is aged monuments of questionable stability. Could it be satellites and a gravity model or even a tested hybrid geoid referenced to a modern national or state network?