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.
Excellent question. In so many cases other errors possible would far exceed the presumed precision.
I have seen a few contracts that stated a certain accuracy total station be used, mostly building construction. If I recall correctly someone told me in the Leica guns it's simply turning it on in the gun (a 5 can be a 1). Its already there you just have to pay to unlock it. It's been a while and I may not be remembering correctly, so take that last bit of info for what its worth.
In long distance control surveys, 1" is a must. When your average leg can be a mile, and 3-5 mile legs, a second here and there can add up.
However, these days GPS has made 40 mile traversing, networks, a thing of the past.
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?
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.
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
As a civil/structural engineering company that does our own surveys for engineering projects, we chose 1" instruments and one of the main reasons for this was so that in the first instance the accuracy of the instrument can't be "challenged" (unless someone wants 0.5" or less). Obviously a lot of other things can be challenged, but we can control/mitigate most of these.
Least count may be better than specified accuracy.
Above referenced doc, for the lazy.
http://www.ngs.noaa.gov/FGCS/tech_pub/1984-stds-specs-geodetic-control-networks.htm#2.1
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 5-inch instrument may be okay for a lot of applications, but often times a bigger instrument is preferred 😉
Sorry for the joke. If I were to only get one instrument, I would prefer to go with one that has more precision than I absolutely need so that when I have work that requires it, I could do it. If I had more than one instrument, I would probably keep the higher-precision instrument a bit more babied and use the lower-precision one when the good gun isn't neede.
Larry Scott, post: 382357, member: 8766 wrote: ...In long distance control surveys, 1" is a must....
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.
Tom Adams, post: 382372, member: 7285 wrote: A 5-inch instrument may be okay for a lot of applications, but often times a bigger instrument is preferred 😉
Ha Ha
Darn few are using a 1" or 5" gun to the described accuracy, which requires at least 2d & 2R. Recently I am doing a 90 acre farm with a mixture of 1,000' foot legs and many 200-300' legs. My traverse essentially encompassed 153 acres with 30 traverse points and 11 of them being GPSed.
Seven GPS points were on the East traverse and the West traverse was started on 2 GPS only points, looped out to gather 2 more and then tied into the East traverse by re-observing 3 successive East traverse points along the South end of the traverse. I then tied in the North end after gaining permission from an adjoiner who I could not contact when I had started earlier. Essentially I held my GPS positions, allowing angles to adjust while holding EDM vectors. Four of the GPS vectors were observable as direct pairs, all others had a traverse point between them. I had 3 1/2 day GPS sessions over 7/6/6 points. While the GPS was running I did recon, advance traverse setting and line cutting. Without the GPS I would have needed at least 6 more traverse points and 3 extra full field days working solo.
The longest stretches, GPS to GPS were 4 traverse legs (3 times). In my traverse were 3 observed triangles and 2 4 legged loops. I had only 5 single side traverse points off my main loops, 200', 300', 340', 340' and the last at 750' was to a GPS pair point.
Anybody think I needed more than a 5" gun?
Paul in PA
Paul in PA, post: 382379, member: 236 wrote: Darn few are using a 1" or 5" gun to the described accuracy, which requires at least 2d & 2R. Recently I am doing a 90 acre farm with a mixture of 1,000' foot legs and many 200-300' legs. My traverse essentially encompassed 153 acres with 30 traverse points and 11 of them being GPSed.
Seven GPS points were on the East traverse and the West traverse was started on 2 GPS only points, looped out to gather 2 more and then tied into the East traverse by re-observing 3 successive East traverse points along the South end of the traverse. I then tied in the North end after gaining permission from an adjoiner who I could not contact when I had started earlier. Essentially I held my GPS positions, allowing angles to adjust while holding EDM vectors. Four of the GPS vectors were observable as direct pairs, all others had a traverse point between them. I had 3 1/2 day GPS sessions over 7/6/6 points. While the GPS was running I did recon, advance traverse setting and line cutting. Without the GPS I would have needed at least 6 more traverse points and 3 extra full field days working solo.
The longest stretches, GPS to GPS were 4 traverse legs (3 times). In my traverse were 3 observed triangles and 2 4 legged loops. I had only 5 single side traverse points off my main loops, 200', 300', 340', 340' and the last at 750' was to a GPS pair point.
Anybody think I needed more than a 5" gun?
Paul in PA
Paul your 5 second instrument is all you need and good enough for probably over 95% of the posters here. But that was not the 1st posters question.
Please read the link that "party chef" gave everyone and you will have some idea when an instrument better than 5 seconds is needed.
JOHN NOLTON
JOHN NOLTON, post: 382383, member: 225 wrote: Paul your 5 second instrument is all you need and good enough for probably over 95% of the posters here. But that was not the 1st posters question.
Please read the link that "party chef" gave everyone and you will have some idea when an instrument better than 5 seconds is needed.JOHN NOLTON
That link is to a horizontal control network specification, where in all probability a 1" instrument is inadequate. I did some work with a 0.3" Leica and it is not for anything boundary line surveyors do.
I have set up to 326 anchor bolts using a 30" transit, one had to be adjusted when checked by a millwright crew. It was for a lathe base plate that was to be set over all 326 bolts at one time. The holes were 1/8" larger than the bolts. Most of that work was with string lines and a plumb bob.
Paul in PA
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.