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To re-level or not on a re-backsight, back to basics

To re-level or not on a re-backsight, back to basics

To re-level or not on a re-backsight, back to basics

This all might sound elementry but:

In my opinion if I were to re-backsight, I would re-level my instrument then re-backsight, then proceed with my shots. Is this wrong?

 I have a co-worker who dissagrees. He will continue to hold the wandering of the instrument and re-backsight, not re-leveling, getting out some error but the instrument is sill out 30 seconds more or less. Then continueing with the shots.

He has been tought this procedure from more than one RLS and will not budge. My mind is having a tough time with the logic of not re-leveling.I have been tought to re-level for the re-backsight.

What would be the proper procedure for a "re-backsight"

Looking for more opinions.

RE: To re-level or not on a re-backsight, back to basics

Sound like you are working with a transit or a survey level.  If you are, I level my instrument at two positions 90 degrees apart over the leveling screws. Once the telescope is level, I still keep an occasional eye on the bubble.  The only time I backsight is to read the instrument height with the rod very close to the eyepiece of the telescope.

RE: To re-level or not on a re-backsight, back to basics

It would help if you clarify your question:

Are you using a level or a theodolite/total-station?

What do you mean by "re-backsight": a check on an existing backsight obs, or a new set of obs that uses the same BS as the previous set?  

RE: To re-level or not on a re-backsight, back to basics

We use a total station.
Lets say I set-up on #2 and backsight #1, then turned 50 sideshots, now the front man is ready to traverse, so I would re-backsight" zero-up" to get out any errors before I shoot the "foresight" traverse point.
Would it be better to re-level the instrument and backsight/re-bs, or just turn, re-zero and not re-level?
I've gotten many answers to this question all based on diffrent situations.  ?
Hope that makes it a litte more clear.

RE: To re-level or not on a re-backsight, back to basics

1. With older analog instruments (transits) I would suggest re-leveling...the error that is introduced by not re-leveling is termed the inclination of the axis.
2. Newer total stations and robotic total stations will almost 100% of the time have level compensators that eliminate the need to re-level assuming that we have not 'bumped' the instrument.
3. It is not necessary to re-zero the instrument by the way. The computation to reduce the angle is to subtract the back sight reading from the front sight reading...doesn't matter what the readings are.

Since this is my first day, I have not taken time to fill out my profile. I am a PLS registered in 3 states and have been a surveyor for 32 years.

RE: To re-level or not on a re-backsight, back to basics

are you surveying to set controls as a surveyor or are you doing onsite construction surveying as the contractor? i might have a comment to throw in based on my past experiences in construction surveying as the contractor depending on what you're doing.

RE: To re-level or not on a re-backsight, back to basics

I agree with your co-worker. When you start re-leveling your asking for problems if there is not a problem.
If your working and the bubble is in the limits, everything is good. Why would you want to re-level if it is in the limits,
If it becomes an issue that you have to re-level, then you would also have to reshoot your shots to be sure with the new level. Won't be much on a short shot but can be alot on a long shot.
If your level is going out of level enough that you have to re-level because your turning the level, then its time to take it in for a tune up.

just remember not to erase any numbers in your field book also. :)


RE: To re-level or not on a re-backsight, back to basics

We do all phases of surveying.
Any comments in any area are wanted.
Always got room to learn.

Limits are a good thing to fall back on but at times the intrest in getting a tighter traverse is tempting. We are always with in "The Limits".
The instrument tends to wander the longer it sits and tends to throw 30+" (on any given axis) then a bit more and then you want to set some control, 500'+ away. 30" to 1' of error would throw you out pretty good on the long shots.
The weather plays a big part in this, the mornings are cold and then the suncomes up and starts to warm up the instrument and it starts to wander.
The instrument is in fine working order.


RE: To re-level or not on a re-backsight, back to basics

i had a leica that did that once. it had the continuous drive (without a lock). it was a great instrument but would wander as you describe.  i now prefer nikon even the leica optics seemed a little better. also, the tripod would move around from early morning to midday due to change in temps on the legs (whether alum, wood, or fiber/wood) so i always made sure to move around regularly enough that my setup was good every so often to avoid having to reshoot points. and since we (contractors) don't typically adjust the traverses, minor movements can quickly get columns out of whack on a med to big sites. i mainly did construction surveying on big projects but worked in pretty tight tolerances (for construction/contractor surveying that is - <0.01' or so closure across my 50-100 acre sites).

if i were setting control out on my sites, i would never stay set up very long. i'd set the control across my sites and then come back to layout individual points that could stand to be out a 1/4" or so (which is actually still tight for construction site/contractor surveying). and if i were shooting points off my control while being set up for a while, then i'd periodically check my bs and zero out if needed. and again, this is coming from my experience as a field engineer as a contractor and not a rls.

RE: To re-level or not on a re-backsight, back to basics


If you will state the instrument maker and model there are some specific comments that I could make as to operation of the equipment.

If the instrument is not available at present a question or 2 will help:

1. Is it an external vernier reading transit?
(This type of instrument requires the most 'stroking')

2. Is it an internal vernier reading instrument?
(Look through an eye piece to read)

3. Is it an electronic total station of some kind?
(The data is read from a screen on the instrument or it is connected to a data collector)

There are procedural things that are different, and generally it addresses one of the 3 questions.


Daniel E. (Dan) Galbraith

RE: To re-level or not on a re-backsight, back to basics

Yes idealy we would set the next traverse point asap, but at times this is not possible.

Dan: we are running with to diffrent Topcon Totalstaions. Topcon GPT 3002w Pulse laser and a Topcon GTS 313 (older). With a data collector.

Thanks for all the input!

RE: To re-level or not on a re-backsight, back to basics

if you are using a newer totalstation that has a hozontal compensator, then i would leave it. but once the gun runs out of level alot i would check your backsight.

but remember also if you DO have a compensator , when you zero out the gun you should hit your backsight!!!the gun is going to compensate for you. if you dont hit your backsight then yes! re level the gun...

alot of people dont like to relevel the gun becasue your work wont be consistent. depends on how tight the work has to be.

ps-if your the chief and your transit man is not re leveling the gun when you tell him too get rid of him! And he must have a reason to not re level the gun other then its how he was taught?taught for what reason?

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