Has anyone ever seen a spec that says you must re-level and re-center between sets? Their use of the word sets means D+R.?ÿ
I have worked for a few that insisted upon making a new setup over the same point and doing a new set as many as 6 times on each point of the traverse.
It was boring and it took longer to do that way and all it did was make the boss upset for the time it was taking.
I know some that would let their IMan go if they were setup on a traverse point over 3mins.
Some people just want to make things harder than they need to be sometimes.
That is usually a requirement for 1st order work.
The purpose of a 'set' is twofold. First, you add another observation, reducing the theoretical error by about 30% over a single angle. The second purpose is to eliminate various errors introduced by the instrument itself. Breaking a setup between sets may be appropriate for some precise work, but doing it in the middle of a set defeats the purpose.
Put another way, that's just plain stupid.
I mis-read the OP. I thought you were saying it required breaking the setup between the angles in a single set. Breaking between sets may be appropriate for some critical and precise work.
I have never seen it as a spec, USCGS special pub 247 Manual of Geodetic Triangulation does not mention it in the procedures except to say..."Do not change the leveling of the theodolite during the observing of any one position. A note should be made in the remarks column whenever the instrument is releveled. The note "levels checked" or instrument or "instrument releveled" should appear at least once near the middle of every set of 16 main scheme observations".?ÿ
The context of my question is we are using a robot, it has an automatic compensator, and if I have to relevel and recenter between each set it requires an instrument operator there to do that, and we are doing probably 2000 sets on a project over a weeks time. Spec requires 4 sets to each point. One setup might have 30 or 40 foresights, done 2 or 3 at a time. That adds another person to the crew. To me it should be sufficient if I check the leveling and centering at the end of each setup. If it is not centered then I would probably have to redo that setup. I use heavy trimax tripods, rarely has one ever moved unless there was a strong wind.?ÿ
Also, I remember a demo when I bought my S6 that if it goes out of level the compensator detects that and corrects the readings. They demonstrated that by putting it a bit out of level and then checking the plumbness of a column that we previously checked when it was carefully leveled.?ÿ
It sounds familiar from an ASTM specification i browsed years back. iirc it mentions three sets of angles turned to a specific tolerance before work begins.
I was only able to browse because I couldn't afford the, roughly, $150 it cost to purchase the document.
I don't know they required a separate set-up between observations.
For statistical analysis of the position of the control point, it would be useful to have multiple setups over each point. Force centering and simply turning multiple sets essentially assumes that your setup is without error (or that you already have determined the error, and it remains consistent across setups).
That being said, it takes a lot more time (and therefore money).
For statistical analysis of the position of the control point, it would be useful to have multiple setups over each point. Force centering and simply turning multiple sets essentially assumes that your setup is without error (or that you already have determined the error, and it remains consistent across setups).
+1
I have seen this spec for some DOT projects and the odd private contract where the client wants a high level of precision.
Personally, if I am turning more than one set (which could be anywhere from 2 to 10 D+R observations), everything gets relevelled and recentered whether it's in the contract or not. Otherwise it is not an independent observation and makes the data look better than it really is.