In real flat areas, where drainage is slow, and sewer flow rates are marginal, and natural flow is critical, then gps is out.
In steeper areas, where flow rates are high, then trig leveling, and gps are mostly fine.
Near flat drains... Watch out.
The old saying "sewer flows downhill, and pick up your check on Friday," also means "try to make sewer run uphill, then pick up your lawsuit, when they lawyer up".
Know what tool, for what job... Also,
If you are in a flat geoid area, gps is pretty good. That is, the geoidial separation is consistent, then less modeling. Where the geoidial separation is in transition, good geoid models are needed.
Somebody else can say this way better than I can. Get the idea from me. And details from others who work these areas.?ÿ
N
?ÿ
When the 2022 datum is released, transfer won't be an issue.?ÿ You will use the ellipsoidal height from GNSS at your project BM and the 2022 geoid model. That will be the definition of elevation.
With the present geoid model that result won't be as accurate to NAVD88 as transfer with GNSS sessions at reliable NAVD88 BMs and your project, with correction for the geoid difference. With a hybrid geoid like 12B or upcoming 18, differences in a region are more accurate than the geoid value at some point. Simultaneous sessions are better than sequential. A careful level run is best.
I've been pleasantly surprised at how well I close vertically with my Leica TS-12 Robot.?ÿ I've now checked it in just about every conceivable way: NCGS benchmarks, static GPS, level loops, etc..?ÿ On 100+ acre tracts I've never been more than 0.04' off and I am usually within 0.02'.?ÿ?ÿ
I get similar results with my Leica 1203.
Ed
The premise of this posting is how to bring datum into a project site , not how to topo after that. I look at static GPS as ?ÿlonger distance height transfer tool, not a short distance transfer tool and certainly not RTK for project BMs short distances apart. Bring your datum into one project BM then set local site BMs more traditionally.?ÿ
Bill
A careful level run is best. Agreed. Sometimes the best is not called for or needed to perform the task at hand and another way can save thousands of dollars in project cost.?ÿ
Nate
I agree with you that a GNSS solution is not feasible for matching into gravity flow systems.?ÿ But with proper use, GNSS is an excellent tool to establish a site on a particular vertical datum.?ÿ Would I use it if a benchmark was reasonably close to my site, probably not.
That being said, I would not never rely on published invert information for design purposes if at all possible.?ÿ Worst case scenario I would calculate the elevation based on relative offsets to accessible features on the same as-built.
I'll give another vote for a digital level. Entry into that market is $1300 if you get a leica sprinter 150 (non-M) including rod. This doesn't store points but could allow you to use someone on the instrument end that wouldn't have to read the rod since the level does that for you. That could give you flexibility being the rod guy with turning points and whatnot if that was a concern.
Mr. Frame,
Your comment about solos surveyors tending to shy away from level runs is forgetting one point.
I believe it depends on just how good a solo guy is at standing up a rod and having it stay there while you walk back to the level to read it.?ÿ
Long time solo guy.
JA, PLS SoCal
Hey -?ÿ if this is in the UK then those "lower order" benchmarks have not been maintained for a long time. GPS is the normal procedure now. You may well still have to level or traverse in depending on the GPS reception at the site.
https://www.ordnancesurvey.co.uk/benchmarks/
5th paragraph
and you wont be doing "boundary" work in UK with GPS as there is no monumented or co-ordinated cadastral system. Deeds may have dimensions of the plot but no monuments or points of beginning. So the role of a land surveyor is pretty much limited to measuring the size of the plot as it currently stands.
?ÿ
I believe it depends on just how good a solo guy is at standing up a rod and having it stay there while you walk back to the level to read it.
My remark was prompted not by possibility but rather feasibility.?ÿ I once ran a 1/2 mile (each way) level loop by myself using a modified aluminum tripod to hold a conventional fiberglass rod.?ÿ Another time I ran a loop (don't recall the length, probably around 1/4 mile each way) in a flat urban area by printing 2-foot rod targets on mylar (see image below) and taping them to light poles (I used a torpedo level to plumb them).?ÿ My experience with both of these techniques convinced me that leveling isn't practical for a solo operator when he has a good robotic total station available.
?ÿ
I believe Mr Meyer said it first and I will strongly echo. Turn through the same physical points going out and back for error isolation. I believe he recommended on a periodic basis, I??ll up that and say do it on EVERY turn. I learned on a multi person crew and, now running solo levels, it is the only way I??ll go. ?ÿWhen a bust happens, you can quickly determine the location of your error while sitting in the truck. Then, it??s a simple reshoot at a known ?ÿsetup for validation and resolution.?ÿ
On a side note: recently in my career, an older field dog/ buddy I know said, you can shoot each turn twice as you move from bm to site bm. Simply break and reset the level between each turns fs/ bs. It doesn??t save any show leather but, makes it a ??one way? trip with the same amount of error capture. I freaking love surveying and surveyors.?ÿ
I'll give another vote for a digital level. Entry into that market is $1300 if you get a leica sprinter 150 (non-M) including rod. This doesn't store points but could allow you to use someone on the instrument end that wouldn't have to read the rod since the level does that for you. That could give you flexibility being the rod guy with turning points and whatnot if that was a concern.
Sprinter will store points but really can't recommend it for precise level loops. Have found it it to give quite a large spread of readings. Even when the loop closes it seems to be more by luck than anything else.
I believe Mr Meyer said it first and I will strongly echo. Turn through the same physical points going out and back for error isolation. I believe he recommended on a periodic basis, I??ll up that and say do it on EVERY turn. I learned on a multi person crew and, now running solo levels, it is the only way I??ll go. ?ÿWhen a bust happens, you can quickly determine the location of your error while sitting in the truck. Then, it??s a simple reshoot at a known ?ÿsetup for validation and resolution.?ÿ
On a side note: recently in my career, an older field dog/ buddy I know said, you can shoot each turn twice as you move from bm to site bm. Simply break and reset the level between each turns fs/ bs. It doesn??t save any show leather but, makes it a ??one way? trip with the same amount of error capture. I freaking love surveying and surveyors.?ÿ
If there is only 1 staffholder then that either doubles or adds 50% to their walking distance. Depending on whether they get a lift back from the far end.
Also I think there are more random elements thrown in?ÿ by doing the extra measurements on the way back. These random elements are what we need to spot errors. ie you don't get the same error twice.
This his raised some very interesting comments. Many, many thanks.
I already have a robotic Total Station so that looks like the best way to go for now. Any recommendations for using it for levelling a benchmark into a site?
This his raised some very interesting comments. Many, many thanks.
I already have a robotic Total Station so that looks like the best way to go for now. Any recommendations for using it for levelling a benchmark into a site?
For most accurate work you would want reciprocal measurements to cancel out the effects of refraction over long sights. This doubles the number of setups as you need to occupy (or set up next to) each point. Otherwise you can just setup on every other point (for transferring levels only).
For what you're doing you should get away with using the default refraction and curvature coefficient. Especially if you're only doing 70 metre sights.
I would advise measuring the vertical angle in both faces. Don't rely on the instrument being in perfect calibration. Although the vertical circle error and the compensator error should be cancelled out with equal sights (in theory at least).
Prism on a pole is best for benchmarks and change points. Using a prism on a tripod means you are introducing target height measurement errors. If you are solo then a pole tripod is ideal for this. Not that keen on walking away form a bipod myself.
As far as booking it - I would set the target and instrument to zero and record the VD (vertical distance) as well as the pole height. If the pole height is the same all the way through the survey you can actually ignore it and just book the average (f1/f2) VD as a backsight or foresight as appropriate. If you are using Trimble Access then "survey basic" is the option I would use.
?ÿ
This his raised some very interesting comments. Many, many thanks.
I already have a robotic Total Station so that looks like the best way to go for now. Any recommendations for using it for levelling a benchmark into a site?
Look here:
https://www.google.com/url?sa=t&rct=j&q=&esrc ="s&source=web&cd=9&ved=2ahUKEwjzwZTs8LveAhWDneAKHeyGDsoQFjAIegQIAxAC&url=http%3A%2F%2Ffgg-web.fgg.uni-lj.si%2F~%2Fmkuhar%2FZalozba%2Ftv%2FTrig_Leveling.pdf&usg=AOvVaw2PFk0azcepA2D12Ie2K4e6"
?ÿ
On a side note: recently in my career, an older field dog/ buddy I know said, you can shoot each turn twice as you move from bm to site bm. Simply break and reset the level between each turns fs/ bs. It doesn??t save any show leather but, makes it a ??one way? trip with the same amount of error capture. I freaking love surveying and surveyors.?ÿ
I had a bad experience with this method. My green rod man lowered the middle section of a 3 section rod at one point (which I had told him never to do), and forgot to raise it back up on one turn. My side-by-side level runs checked quite nicely. This was for photo control, so the 5' elevation error became apparent when the photogrametrist was setting up the photo model in the stereoplotter.
I believe Mr Meyer said it first and I will strongly echo. Turn through the same physical points going out and back for error isolation. I believe he recommended on a periodic basis, I??ll up that and say do it on EVERY turn. I learned on a multi person crew and, now running solo levels, it is the only way I??ll go. ?ÿWhen a bust happens, you can quickly determine the location of your error while sitting in the truck. Then, it??s a simple reshoot at a known ?ÿsetup for validation and resolution.?ÿ
On a side note: recently in my career, an older field dog/ buddy I know said, you can shoot each turn twice as you move from bm to site bm. Simply break and reset the level between each turns fs/ bs. It doesn??t save any show leather but, makes it a ??one way? trip with the same amount of error capture. I freaking love surveying and surveyors.?ÿ
If there is only 1 staffholder then that either doubles or adds 50% to their walking distance. Depending on whether they get a lift back from the far end.
Also I think there are more random elements thrown in?ÿ by doing the extra measurements on the way back. These random elements are what we need to spot errors. ie you don't get the same error twice.
An alternative is to have 2 turning points at each. Have 2 screwdrivers, one with a red handle,?ÿ one with a blue.?ÿ Rodman hammers both in the ground to use as turning points. Preferably with the 2 having distinctly different elevations. Keep the blue readings on the left page of your field book and the reds on the facing (right) page.?ÿ ?ÿ
Note a level out of calibration will accumulate error of unbalanced legs on the run out and if the same set up and turn points are used on the run back in, all of this accumulated error will be compensated and your data will indicate your loop closes very well even though it actually may have a significant amount of error. Balanced FS & BS will eliminate this error. A perfectly calibrated level will eliminate this error. Checking turn points of the run out on the run in is a good idea, but it should be coupled with differing set up locations so error can be detected instead of compensated.