Hi there! I am shopping for a new total station and trying to decide which angular accuracy makes sense. The classic versions everyone is used to are 1", 3" and 5", but then there's the select few 2" instruments that are out there as well. Most of the time 3" instruments are used for doing topo/boundary and construction layout but if you ever do any monitoring it's typically a 1" instrument. My question to the community is what is the value, if any, of going with a 2" instrument? It seems to me there isn't much of a need for this type of a angular accuracy other than maybe having a slightly tighter traverse/topo shots compared to a 3". I presume these 2" instruments don't meet most monitoring specs so that's why I'm curious what purpose these types of instruments serve. I am finding some good pricing on used ones but wondering if I should look for 1" instruments since they have a broader use. What are your thoughts??ÿ
I've been using 2" robots for about 10 years now (first Leica, now GeoMax).?ÿ To me it's right at the sweet spot for general use.?ÿ I had a 3" Topcon manual instrument before the Leica, and my work tightened up considerably after going to the robot.?ÿ I don't image much of that improvement was due to increased angular accuracy, though.
Going to 1" costs about $1,700 in a GeoMax.
For most small-scale monitoring projects that I've undertaken, other error sources (e.g., centering error, HI/HR) dwarf the angular error, so the lack of a 1" instrument hasn't been a problem for me.
You will not get 1" results out of a 1" gun unless you also get 1" tripods, tribrachs, and glass - and keep them in 1" adjustment and condition.?ÿ?ÿ
A 1" is more about the certificates over here. You cannot explain to a client that 1" has to be taken with a pinch of salt if not used properly.
Heard at Topcon that a 1" is 2000$ in difference so i'm thinking of replacing my 11 year old robot with a 1" anyway next year.?ÿ
If I'm going to run it manually, 1" is probably not worth it. At my age I have three second eyeballs (at bet). Lol
Seriously, it's about the work you intend to do or may pursue. If there is any chance you'll need it it's a small sum and I would go for it.
1 second is about 1 mm at 200 meters (0.003 ft at 200 yards).?ÿ That may be useful for monitoring, but you certainly don't need it for lot surveys or even most building layouts.
As others have said, there's a lot more going on.?ÿ You are probably better off with a less accurate gun and multiple measurements with re-centering and re-leveling.
I have three second eyeballs
Good visual acuity is about 1 arc minute divided by the magnification of the telescope.
@bill93 So a 30 power scope with good eyes equates to '2 second eyeballs' for purposes of this conversation...
I have a very good 2 arc second survey instrument. It also estimates to 1 arc second. I notice the difference (much better) that the other instruments I have used in the past.
Of course, all of the advice here about proper technique applies. Once I attended a seminar on how to make you measurements more precise, and I expected some discussions about technology, but was surprised to hear that checking the tightness of screws and bolts on the tripods was mentioned.?ÿ
I have always run a 3? total station for my boundary and Topo work. The occasional monitoring job (about one a year), I get by by running sets of measurements.
What I have discovered from doing this for a few decades, is that to get 1? accuracy from a 3? gun is that I run a set of 5 measurements, and ignore the first two sets. I don??t know if it??s the instrument (Leica, topcon and older Trimble), or my eyes, but most of the variation occurs in the first two sets, with the last three being very consistent.
Some 1" instruments also have better EDM, tribrach, optical, plummets. I ran 3" guns for 20 years and thought the same as most of you. But after running a 1" and 1/2" instrument I'm convinced there is more to it than just the angles.
3", 2", 1", in the vast majority of situations, it really makes no difference, especially with compensating errors and a host of methods to adjust data.?ÿ If you are not doing first order work routinely you need not be concerned in 1" or 2" guns and accessrories.
Stated accuracies really don't matter with out the proper accories and strict adhereance to proceedures.?ÿ My crews run 2" Leica guns and have retraced surveys that I worked on in the early 80's when I was running a 30" K & E optical transit and interpolating down to 15". I've never come across one of the corners setback then that did not match within hundredths or at most, a tenth, even though the points were set some 30 years or more ago.
You don't need a 1" gun to meet the vast majority of minimum closure standards where a 5" gun will do just fine.?ÿ Combine that with the fact that most people are using GPS now and on larger projects, a combination of both terrestrial and GPS methods will yeild a very high accuracy H & V constrained network if the person processing the data know what they are doing.
