Turning Sets - State Specific?

Result's Based Positional Tolerance Of Precision

and be able to prove it.

Sets allow one to utilize statistics in the proof of your work.

There are those on the board that believe they achieve precision without sets. I have my doubts that they can prove it.

Paul in PA

California does not have technical standards so there is no specific requirement to turn sets but it is good practice.

Some data collectors allow you to turn all the BS observations then all the foresight observations but those aren't true independent sets. If nothing drifts then it wouldn't matter but if something drifts between BS and FS there would be no detection of it.

metes and bounds... not meets and bounds...

This is one of those urban legends in surveying. I remember the seminar folks in Texas saying that Texas required sets. They based this on the rule requiring a surveyor to use his equipment according to manufacturer's recommendation (I'm paraphrasing - which is what leads to the very urban legends I despise... so I'm a hypocrite, sue me). The manufacturers base their angle accuracies on a forward and reverse pointings, so in order to get the manufacturer's spec'd accuracy, you'd theoretically have to turn a set.

In actuality (just like the old "no erasures in fieldbooks myth") there's no requirement in Texas to turn a set. Having said that, I do turn sets on all traverse and boundary monuments, unless I'm just verifying work we've done in the past.

What Paul said

It is always wise to turn sets on traverse for many reasons.

To achieve reproduceable results
To catch obvious errors and blunders
To achieve a better result than what your instrument can turn on one reading.
To save a long walk since the most frequent occurrence is always the greatest distance from the end of the road.

I have been surprised by the different methods others have used to turn set. The biggest of which was the want to zero the gun and turn to take a single angle reading six or more times in a row and average those angles.

Once I was taken off the instrument and almost fired for properly turning sets by taking direct and indirect sightings and flopping the telescope between turnings and accumulating the readings.

That bunch tried to ruin me for life by trying to make me cut corners.

0.02

Near 0. Face 1 bs...f1 fs...flop...f2 fs...f2 bs; near 20. F1 bs...f1 fs... Flop....f2 fs....f2 bs...etc...around the plate.
With multiple tripods a multiple set takes only minutes.
Zenith angles and slope distances fore and aft..
DDSM

Almost the same, I put about 20 seconds on the circle to keep from going back past zero and complicating the averages. Two sets were always turned and sometime more, divided the starting degrees according to the sets intended to be turned so the whole circle would be used. Could turn a couple of sets to multiple, including the verticals direct and reverse. If keeping your own notes the field book would be tucked under the left armpit. Could do that faster than the time it took to switch to the EDM and hook up it's battery. If less than 300 feet the distances was usually chained, took a lot of strength to hold that chain up to the mark on the gun while hollering pull harder.
jud

> I think they all are good practice. But are they always practical?
>
> Just curious of the different points of view...

Well, I'd say that if there isn't enough time to make a survey correctly, there darn sure isn't enough time to do it incorrectly.

That's the whole point: the few minutes that measuring important angles on both faces usually requires *total* is inconsequential. It's nothing in terms of the total time spent making a survey. However, it improves the quality of the work enormously.

In Texas, the TBPLS has adopted certain Minimum Technical Standards regarding positional accuracy. While they have wisely not specified methods and procedures for surveys, except in a general way, any surveyor who is just measuring angles to control points and boundary markers on one face, one time, is not going to have an adequate basis for claiming that his or her work meets those standards unless the conventional measurements are a purely redundant check upon positions determined by other means such as GPS methods.

I hated working for a crew like that. "Hurry up! Hurry up! We just need to do one direct to get it done. You're wasting time!" (On a 200 acre boundary survey with extreme vertical angles)

....turns out you waste a lot of time when you have to do everything over again, like they had to. I left after that.

Another one I liked... "Why are you taking so many shots? The fence CAN'T bend that much!"

Yeah, I'm just taking shots for the fun of it. Good riddance to that crew.

With A robot...

I'm not sure how 'necessary' it is, but I turn 2 angles to all traverse points and almost all boundary corners.

Keep in mind 90% of my surveys are on parcels less than 2 acres.

With A robot...

I make it a practice to turn at least 3 sets to all control and monument ties. Many moons ago, back in the mid 90's, while working for a larger engineering firm I numerous instances where our crews would turn the 2 set minimum only to get into the office to find that they did not jive. Since you only had 2 sets you would have to go back out and return the angles. From that point on I started utilizing the 3 set minimum, that way you can figure out which one was bad. With the advent of robotic instruments the added time is well worth the insurance.

As for taking the sets from different positions on the circle, I don't think instruments have used a true circle in decades, they use encoders. That procedure was to reduce the error do to manufacturing errors.

With A robot...

I'd think an encoder would have the same potential errors as older glass circles. I haven't seen an actual modern encoder, but it has to have something that moves in a circle and causes counts. A big part of the error is likely to be due to out-of-round and off-center, and using more parts of the range still helps.

With A robot...

> I'm not sure how 'necessary' it is, but I turn 2 angles to all traverse points and almost all boundary corners.
>
> Keep in mind 90% of my surveys are on parcels less than 2 acres.

Same here. And my DC is set so that if any angle is out more than 30 seconds I get a warning. I usually try to re-turn it, but if I'm within 100' of the instrument, I'm going to consider other things... Is it 34 seconds? Is it a steep angle? Lots of variables. I've never let one go that was over 40 seconds, but I was only like 30 feet from the instrument and about 10 difference in elevation. Lots and lots of small decisions like that.

Carl

I think that since there is flexibility in that I can use a K&E 1' Paragon or my Trimble VX 1" robot, then one could say that positional tolerance would imply sets under certain conditions.

When I began running a run in the VERY early 90's, we still had a GTS 2B. If you didn't double the angles, you couldn't verify that you were level. Same with the transits. You better double the angle to check the plate. Now, with dual action compensators and electronic plates, that may not be necessary, but you will ALWAYS find out if your gunner has the sucker level if you double the angles.

Also, as others have said, the DIN specs on the gun are based on best case scenarios in a controlled environment at a statistical level. All the stats classes I had required multiple observations to begin to build the curve and set up confidence intervals and determine standard deviations (N-1 please). So again, if you're doing an ALTA and certifying to it in Texas say, and TBPLS minimum standards of practice state that if you certify to an ALTA you better meet the specs, and the ALTA specs say that you have to certify at a 95% level, then yes, the implication is that you as the instrument man, surveyor, et cetera, better be doubling the angles because you can't really state based on single observations what your confidence level is as no measurements are error free.

Like I said, I could argue it both ways if I wanted to, but in this case, under certain circumstances, I'd say that it can be required.