All truth told, MOST users will not be ABLE to tell the difference between a 1" and a 2", and a 5" gun.
The NUMBER of things that HAVE to work right, such as:
Tripod head, and the leg pivots, and the heat, (umbrella, if there is sun) and the CARE and lubrication of the tangents, and the temperature of the gun, (direct sun, with your head shadow) will mess with it. I learned to turn angles FAST, so that temperature did not effect it as much...
The choice of the software setting, of 5" or 1", does not CHANGE what the gun can do.
Also, the overall design, effects it.
For all the LONG distance work, go GPS. No point wasting time cranking angles.....
N
A 1 second gun can do everything that a 5" gun can do, but a 5" gun can't be a 1 " gun. If you ever have projects that require a 1" gun you have 2 choices, piney up a few more bucks and buy the 1" gun rather than a 5" gun, or rent a 1" gun. Run the numbers and see which one is best for you.
Back in the old Set 2, Set 3, and Set 4 days the weight of the instrument was significant. Now they seem to be very similar in weight.
We have a little project that we spend about 3 months on each year. I just placed an order for a quote on a LEICA TM50 that is a 0.5" instrument. It won't do everything that our total stations will do such as power search, but it does have the ability to Autolock at 3,000 meters, and the Autolock accuracy is 0.5".
Totalsurv, post: 382349, member: 8202 wrote: On the thread below by rfc the use of a 5" instrument was questioned. I use a 5" instrument all the time and was just wondering what situations would require a higher accuracy instrument and whether a 3" or 1" would be used. Outside of industrial applications I could only see a higher accuracy instrument being used for anchor bolts maybe.
I'm going to say that it's horses for courses. If one has the ability to get reliable +/-5mm s.e. positions with GNSS, then when those positions can be interspersed at intervals with conventional traverse and combined in a least squares adjustment with the conventional measurements, that takes quite a bit of the strain off a total station for most land surveying purpoes.
The other element to the problem is that of testing a particular instrument to determine what the actual uncertainties in directions taken with it are Unlike Leica, some manufacturers do underspecify their instruments.
Monte, post: 382359, member: 11913 wrote: This discussion goes round our office on occasion, with the focus being on just how large a second of a circle is at a given distance. At 10,000 feet, a second is 0.04 of a foot. We report our findings to the nearest second for good closures, but for nearby work, just how wide is a prisim pole?
I like to use the rule of thumb that one second = 0.01' at 2000 feet. This is an approximation, so your number is probably more accurate, but it works well for almost anything I ever need to use it on.
Totalsurv, post: 382349, member: 8202 wrote: On the thread below by rfc the use of a 5" instrument was questioned. I use a 5" instrument all the time and was just wondering what situations would require a higher accuracy instrument and whether a 3" or 1" would be used. Outside of industrial applications I could only see a higher accuracy instrument being used for anchor bolts maybe.
A situation would require a 1" gun if you worked backwards from the positional tolerances needed for a job and only that 1" instrument would allow you to meet the tolerances. In order to realistically determine this it would be in your interests to know how the errors appear in your readings. and it'd be really cool to know the maximum angular error your instrument can throw up, so you could figure out your absolute maximum positional error at the setout/reading end. That way you don't have to rely on the only partly useful ISO or DIN spec.
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.
