When purchasing a total station, I assume one considers the precision requirements of the type of work typically performed. There is a lot of discussion at work on this subject. A particular concern is setting property corners. Assuming your requirements are to the nearest 0.01’, what would be your choice of a total station based on precision?
1", 1mm +/- 1 ppm
For setting property corners a 5" gun is more than sufficient. Also, remember that to come close to the guns performance you will need top quality tripod, tribrach, target rod, and glass in top condition.
@ Norman_Oklahoma
I did mention ancillary equipment during the discussion and using sound methodology. One guy is concerned about the possibility of going to court over setting a property corner that wasn’t set right because we only use a 5” instrument. This guy wants to buy a 2” or a 1” instrument.
Whether you use a 5" or 1" gun, do you really think the next guy is going to come up to the same location within 0.01 or less?
@ chris-bouffard
Absolutely not.
Field Dog you can turn enough sets of angles with a 5sec gun to get the same results as a 1sec gun. He can alleviate his proprty corner concern without the need to purchase a new instrument.
@ lurker
Like I said, it’s how you set it too. Eventually we’re going to buy a new total station. I think we should buy one that meets our job requirements. We normally only use ours to locate property corners when our GNSS rover can’t get fixed. It’s very rare for us to set property corners. This is the first time in the eight years I’ve been with the county that we’ve done a deformation study.
I would expect any survey grade total station would be able to meet the state's accuracy requirements for boundary surveys assuming it's used correctly.
IMO the sweet spot between precision and cost is the 3" model. They don't cost much more than the 5" model and you aren't going to get much extra out of the 1" model with going to extraordinary procedural lengths.
One outfit I worked for bought a single 1" gun so they could say in their marketing material that they had that capability.
For setting property corners a 5″ gun is more than sufficient. Also, remember that to come close to the guns performance you will need top quality tripod, tribrach, target rod, and glass in top condition.
You will rarely see a setup where the setup from the ground to through the tribrach, out to the prism and back + the training of the crew + the needs of the job is sufficient to be useful for a 1" instrument.
For instance, look through the Leica catalog. There is a big difference in price between the tribrachs, legs, prisms, etc. at different quality levels.
Are you shooting to a rod with a circular bubble?
What are your state's accuracy standards? The 0.01 ft is most likely a requirement for resoluttion expressed on a plat, but the accuracy spec will be more like 0.05 or 0.10 ft for city lots and some ppm for large parcels, or else a 95% confidence least squares limit value.
Put some distance numbers on the angle value. At a quarter mile, 5 seconds is 0.03 ft. And repetition can tighten that. You have to have careful adjustment of your plummet, level, centering, and sighting to get that good even with a 1 second instrument.
One guy is concerned about the possibility of going to court over setting a property corner that wasn’t set right because we only use a 5” instrument. This guy wants to buy a 2” or a 1” instrument.
(Chuckles)
I want to see that court case. Many of the corners I recover were set with 5' instruments, much less 5". If you are using GPS most of the time, your 1:XXXX on a 300' line exceeds a 5" instrument by an order of magnitude or two. If I agreed with my own property corner within 0.01' I would be surprised.
Unless doing high end work on control surveys, 1" guns are overrated. In today's world of GNNS and constraining control networks with a variety of tools, 3" guns or 5" guns are fine. People seem to forget the results that we got with interpolating the verniers on 30" optical instruments, using proper procedures.
My survey instrument is rated at 2 seconds and estimates to 1 second. I think it helps me get repeatable results in both horizontal and vertical measurements quickly. While I agree that turning muliple sets of angles may improve the precision of the result, I rarely get differences of over 1 second with 1 set of angles (2 direct and 2 inverted).
Other factors are needed to improve precision. 1.) A rotating tribrach adapter with optical plumment rather than an optical plummet in the tribrach. 2.) A heads-up detachable bubble rather than the circular bubble that is integrated in the pole. 3.) A bipod for use with the pole. 4.) Making sure the tripods are of good quality and that all the nuts and bolts are tight.
