An alternative is to have 2 turning points at each. Have 2 screwdrivers, one with a red handle,?ÿ one with a blue.?ÿ Rodman hammers both in the ground to use as turning points. Preferably with the 2 having distinctly different elevations. Keep the blue readings on the left page of your field book and the reds on the facing (right) page.?ÿ ?ÿ
That has some merit but a) won't catch the rod setting error mentioned above, and b) means you either have to have a lot of screwdrivers or you can't come back to check the same temporary points in case of a bust.
thanks again guys for your helpful input. I'm going to go for trig leveling using my robotic S7.Will probably hand book to start with although I did just find out about a leveling app for Trimble Access that looks pretty good.
I did think about inviting my missus to help me with my leveling on a weekend buts its hard enough to get the family to hold a staff when doing a 2 peg test for a automatic level.
As I work solo levelling is a problem unless I drag someone out for the day which I'm reluctant to do
What does your wife/partner do? Running levels down a country lane at dawn on a Saturday morning is therapeutic and can be a bonding experience.?ÿ
Daniel,
That ship sailed about 20 years ago.?ÿ I had my wife help me on a job and made the mistake of telling even a monkey could do it.?ÿ That was the last time I ever even dared ask her for help in the field.
I bet there are several thousand stories that could be told by contributors here of "special" surveys of topography while utilizing a helpful wife/main-squeeze on a remote job site.
Let's save a few thousand crew hours for forum readers and their clients over the next few years (perhaps not quite thousands).
There is no benefit to balancing each foresight and backsight - you just need to be sure that your cumulative foresight/backsight distance total is in balance on the last shot to a TBM or BM or anything else that you plan to have an elevation on.
The digital levels ability to keep track of cumulative distance is one of it's greatest time saving strengths (as well as no note taking errors, no mis-reading the rod, no data input errors....)
I think you are right about equal totals taking care of a slight and fixed sighting angle relative to level.
But the curvature and refraction corrections are not linear. Correction = k d^2 for appropriate constant and units, and sign.?ÿ
Therefore mismatched foresights and backsights are not necessarily compensated by matching only the sums of distances.?ÿ There is a tendency for the errors to cancel when the totals are equal, but it won't be exact for most distributions of distances.?ÿ Is it good enough for your project? Maybe.
For the case of just two turns with ?ÿ?ÿ Da and Db?ÿdistances between turning point pairs, ?ÿ?ÿ Xa first backsight distance, ?ÿ Required total backsights = total foresights, Some algebra results in Correction/k = (Da - Db)(Da - 2*Xa)
Thus the corrections cancel if the turning points are always the same distance apart or if the backsight is half the distance between turning points.?ÿ If the point pairs are not the same distance apart and you don't set up in the middle, there is an error that could be significant.?ÿ With more legs in the level run, it gets too messy for simple algebra, but this is part of what is going on.
If you are using a level with curvature correction (like the Leica DNA series), this is a non-issue if curvature correction is turned on.
If your level doesn't correct for curvature, I believe that in practice, this error nearly always balances out as the FS/BS differences accumulated going up a hill are cancelled out by the FS/BS differences going down the other side - in situations where the run is predominantly uphill or downhill, the turns that you make to get back into balance before reaching your TBM/BM should be of the same magnitude of imbalance as those that got you out of balance in the first place.
This error source should definitely be considered and accounted for on very precise level runs.
All in all - being able to run out-of-balance through the hills can save a large quantity of time without negatively impacting the functional results for all but the most precise level runs.
I'm lazy so I'd say its to far 😉 Great points made prior and I've used may of the suggested methods. I've had a similar experience, having to do a 10km loop from one geodetic marker to another and had to be within 10mm when we closed. It took a while but I had the rod man do most of the work. I'd adjust one of the legs and get a new HI and have him mark on the ground where he was run back and forth between the marks he made on the ground and shoot the BS and FS again. It may not be the preferred choice but we had to get it done.
Of all the tasks in surveying, the one dimensional level run for a mile round trip is about the easiest. 1/2 mi is short. Checking an auto level is a quick and routine task for the odd short day or rainout.?ÿ
A pair of permanent points with very well determined elevation difference in the parking lot is normal in my experience. one quick eccentric set up and adjustment is checked.?ÿ
I find the biggest error is a Philly rod that when extended has a missing or extra hundredth.?ÿ
