JOHN NOLTON, post: 382366, member: 225 wrote: Very simple question to answer. Look at "Standards and Specifications for Geodetic Control Networks" Sept. 1984, pg. 3-1,3-2,3-3 and 3-4 where they talk about Triangulation and Traverse. On pg. 3-2 is a table for Triangulation and it states that you need a Theodolite with a least count of 1.0 seconds for Second order Class 1 to Third order class 11. On the top left of pg. 3-4 is a table for Traverse (which most surveyors do on this board) and it shows that a Theodolite least count of 1.0 seconds is needed for Second order Class 1 through Third order class 11.
Astronomic Azimuth for the same order of survey above require the same Theodolite of a Least count of 1.0 second.
JOHN NOLTON
That is one very eye opening document. Thanks. Even if trading in my 5" gun for better were possible, I'm going with Mark Mayer's idea that tightening up procedures and calibrating and maintaining equipment can have as big, if not bigger impact on practical results.
My T2 worked very well to run control on larger jobs, coupled with a Topcon distance meter or the long range HP it would close very well doing large traverses.
Then I got a 3" Topcon total station and closures were degraded. Still, they were "good enough" and since we were generally working in NAD27 our results swamped the control anyway........
I don't think there were any jobs that the 3" gun couldn't handle, you just needed a bit more adjustment....
Closures were usually 1:100,000,,,,sometimes better. Bit better with the T2, pretty good with the Topcon.
Mark Mayer, post: 382374, member: 424 wrote: If you use a 1" gun in the same way you use a 3" gun, with the same tripods and tribrachs, the same glass and targets, the same field procedures, you aren't likely to get 1" splits, or anything like it, in your doubled angles. Even if you have long sights.
Mark I am not sure what you mean by "splits". If you mean the difference between a direct pointing and your reverse pointing to the same target then it does not make much difference what the split is.
The reason is it could be 30" and as long as it is a near constant for the pointing's its OK. A split will tell you several things(not counting your pointing error)
and that is your collimation error(how well your instrument is adjusted) and if you start to see a split where it was fairly constant before, your level (plate level) on the Theodolite might be getting a little off. In older instruments (Wild T2 , the ones without automatic vertical index) if you were recording you might see a split in the vertical because the " New Observer" forgot to bring the split level bubble into coincidence (beer time).
One would like to have your split "small" to make it easy to mean the directions (or angles; which ever method you use).
JOHN NOLTON
Long Road Engineering Surveys.
+/- 5" at each traverse would add up over the entire length. but that was before GPS came into play. we now adjust at every 2km using either RTK/static observations.
FrancisH, post: 382580, member: 10211 wrote: Long Road Engineering Surveys.
+/- 5" at each traverse would add up over the entire length. but that was before GPS came into play. we now adjust at every 2km using either RTK/static observations.
FrancisH. Why not do the whole Traverse with GPS? (Static)
JOHN NOLTON
Back about 20 years ago our total station was in the shop and we rented a Topcon 300 series that displayed to the nearest second. The party chief on this crew was a grizzled old veteran. We were doing some layout on a large wooded tract, and the instrument man was having trouble turning the angle to the nearest second. Finally the crew chief had enough and hollered, "our other gun is only 5 seconds, get it to within 2 or 3 seconds and let it ride!"
In everything I've ever done, including building layout, a 5" gun has been more than enough. Before 1994, we had 20" guns and laid out two prisons with them and they were only single compensator guns. If the gun is in adjustment, you can truly measure everything to the 1/2 hundreth with a good chain (standardized and temp corrected), and a 5" gun. I've laid out many buildings with this method and with enough checks, works well.
[USER=327]@Scott Zelenak[/USER] is the only person I'm aware or who would probably need higher accuracy from a gun than 5". I have no idea, nor want to know, how he achieves the precision he does with the structures he lays out and builds. So much more goes into his work like compaction of steel vs. concrete, et cetera that I'm very sure my methods would fail past a three story structure.
Otherwise, it's surveying, not swiss watch construction.
FrancisH. Why not do the whole Traverse with GPS? (Static)
Not sure if this applies to your neck of the woods, but here in Singapore, both sides of the road are occupied by high rises. When I say 'high', I really mean HIGH. Most of the time, even static would give out float solutions. Nevermind about RTK radio signals. So what we do is to locate some traverse stations in parks/open rest areas along the road and hope that GPS signals are ok.
In New York, the MTA requires the use of 0.5" instruments for tunneling projects.
monitoring projects would require a 1" or 0.5" instrument.
FrancisH, post: 382711, member: 10211 wrote: Not sure if this applies to your neck of the woods, but here in Singapore, both sides of the road are occupied by high rises. When I say 'high', I really mean HIGH. Most of the time, even static would give out float solutions. Nevermind about RTK radio signals. So what we do is to locate some traverse stations in parks/open rest areas along the road and hope that GPS signals are ok.
FrancisH, Thanks for the information. Been to Singapore in 1967 (RR from Vietnam) so I now understand your problem.
Hope all is going well for you.
JOHN NOLTON
Today was a good example. We are monitoring a very large structure where new underground mining (blasting) is happening nearby. We did two obs in November, 1 in December, 1 in January, 1 in March, and one last week. The obs last week show a 1 cm movement of the two main stations on the structure (not apparent in previous surveys). There are a bunch of secondary points, but they all depend on the two main points. I went back today to check, and the angle today agreed with the angle last week by 0.4" (289 m and 158 m sights to very carefully centered tripods). This is a jump of about 10" in the angle from the previous epochs. I am still analyzing to determine if those points (and the whole structure) moved or if the reference station moved (which is off structure). I have data from multiple GPS receivers and a 1"/1 mmå±1 ppm total station to analyze. The structure weighs about 2.5 million tons (1.25 million tons of concrete).
We recently installed two new stations off structure, but last week was the first epoch for those. Future surveys will use those as well, but unfortunately we don't have prior data, as those would tell me a lot more.
If you consider pre GPS, pre EDM, and you had to determine a position by resection, from points 20-50K feet, or more, away, you'd need a true subsecond angle.
With a 1" second T2, the procedure is a bit more than 2 D/R sets. But manageable, like 16 sets, or more. The rules of statistics apply. A 5" gun takes more work, but not impossible.
And 1" angles were measured before 1" instruments were available.