Several Questions.
Are you using internal software or a data collector?
Do you book your raw data traverse setups in a field book?
Are you shooting and storing your backsight shots D&R (angle and distance)?
Are you shooting and storing your angle sets backsight shots or just assuming that it is forever holding zero.
Are you shooting your traverse points at the beginning or end of a setup?
I would like to see your traverse raw data file.
I suggest a test setup on a central point and at least 5 random angle distance points. Shoot a full set, then turn the instrument tribrach 120?ø on the tripod, shoot another set and then rotate again. What you want to look for are inconsistencies in the horizontal angle reading.
Many years a go I rented a Nikon for a few days work. First day I noticed inconsistencies in my traverse sets. I carefully watched the horizontal angle readout and saw that it would increment second by second then all of a sudden jump 20 seconds. I returned it and the next day borrowed a 5" readout Topcon 3B and got far better results. I never got an explanation of what was exactly wrong with that instrument but it left me open to all kinds of possibilities for errors.
Paul in PA
Dan Henry, post: 441460, member: 10756 wrote: ...swapped instrument out with other instruments known to generate good closures, replaced tripod legs with brand new, verified plummet is calibrated. basically everything we could think of.
when you swapped the instrument out with another good instrument, did the good instrument produce good closure?
paden cash, post: 441488, member: 20 wrote: Any tribrachs getting checked/ calibrated at the same time?
What kind of shape are the tribrachs in? Once upon a time I came to work at a place that had just bought new instruments, but had not bought new tribrachs or tripods. They did have a couple of newish tripods, ones that were not in as tough shape as the others. And they would send the tribrachs off regularly to be adjusted at the dealer. But these tribrachs were pretty long in the tooth.
The crew came back claiming that the new instrument wouldn't hold its backsight - wanted to send it back. They would zero the instrument, turn away from the back sight, then turn back and be 30" off zero. We went outside for a demonstration and it did just that.
I had them set the instrument up on a different tribrach. To their surprise, but not mine, the instrument held it's zero. Tribrachs have three little contact point in them and if those get too worn that will be a problem. That and the whole mechanism gets a little jangly when it wears out.
Mark Mayer, post: 441539, member: 424 wrote: They would zero the instrument, turn away from the back sight, then turn back and be 30" off zero. We went outside for a demonstration and it did just that."
Expansion/contraction of the tripod legs will produce that effect as well. Sometimes severely.
Have you run a test network? A box with diagonals and a point near center. Turn all the angles and see what starnet says about how well the angles fit. The occasional errant angle, mostly very good, or high occurrence of errors.
In a traverse you can't tell if it's only one or two shabby angles with most of the angles being very good.
Wedge targets in tripods. Not fond of staking poles for trsverse.
I had a party chief one time run a traverse a mile and a half up a straight road, come back into the office and tell me my GPS control was no good because he did not close by a foot and a half. I entered his traverse into StarNet and found angular residuals at each statio about -22 seconds. Knowing a little bit about how this Chief operated, I asked him what his horizontal columns toon correction was set at on his instrument. It was within a few seconds of 22.
His standard procedure was to regularly check and reset the columnation correction on his instrument and he must have had a bad setup or sight the last time he did it.
Check your horizontal columnation error setting on that instrument. It doesn't matter how long ago the instrument was serviced. The columnation error can change.
I can't see how the colmination would be an issue if you are turning sets
For your consideration tonight we enter the realm of precision.
In a 2 acre yard there has been a three hub traverse with a central point to sideshot from each hub.
Nobody gets to run the gun on a job until they can pass the test of running that traverse and having the 3 sideshots to the inside point being within the size of the head of the 60d nail.
Using various 5sec guns, the results have been less than a hundredth difference for the last 30yrs.
With today's instruments, the angles should be near perfect on the double and the error per setup should be no more than 3sec on a 5sec gun.
If you are beyond that.........
Your have been in the twilight zone too long.
A Harris, post: 441584, member: 81 wrote: With today's instruments, the angles should be near perfect on the double
why?
and the error per setup should be no more than 3sec on a 5sec gun.
why? what is a 5" instrument then?
If you are beyond that.........
...then in some cases you got what you paid for. i can speak about modern leica instruments at least. and in a single setup, depending on the configuration of the stations, a 5" leica instrument could throw up to a 10" error reading D&R. it could do this straight from the factory in perfect adjustment, working 100% as the factory intended.
imaudigger, post: 441545, member: 7286 wrote: Expansion/contraction of the tripod legs will produce that effect as well. Sometimes severely.
Or, more importantly, tripod joints that need tightening will degrade the results of measurements made with an otherwise nominal instrument mounted on the tripod. That is something so obvious, though, that I doubt that's the problem in this instance. It's probably some procedure that is being overlooked, like running some internal calibration programs to update the compensator and collimation corrections.
Might be the rodman.
I would have all instrument operators to set on the same point and turn to the same BS & FS by setting their instrument up each time for each man.
Watch them closely and let them do it their way without instruction.
Compare results and discuss each other's techniques afterwards.
Running an instrument is an artform to some and others are simply using a tool and just can not grasp what a fine tuned machine is capable of producing.
I really miss the IMan rodeo that surveyors would participate in at gatherings.
For everyone to get has on use a T2 and turn one angle for a reading and compare to the baseline that has been long established.
Larry Scott, post: 441553, member: 8766 wrote:
In a traverse you can't tell if it's only one or two shabby angles with most of the angles being very good.
Actually, if you have one dud angle this can be done simply, especially if most of the angles are very good.
If you have a fully closed traverse where all the interior angles have been read then you calculate the coordinates of each station both forwards and backwards from a common starting line using the same azimuth. The coordinates will converge/be closest at the station where the 'shabby' angle was measured. If the misclose vector is about perpendicular-ish to the station found with this method then you'd have good reason to go back and re-measure this setup.
This blunder type scenario is one ideally suited to inspection by a robust L1 adjustment as opposed to least squares.
I can't buy the optometrical angle as an excuse. Barring something along the lines of macular degeneration, any ocular bias will remain constant once the correct focal length is dialed in.
What sounds likely is the factors mentioned by other posters, such as; an ill-fitted, or, out of adjustment tribrach, tripod legs not maintained, or suited to the swings in temperature. The instrument itself needs to be re-calibrated for the application, or for the swings in temperature; roughly every 40??.
Giving your instrument enough time to acclimatize and settle is a factor. If you bring your instrument out from the air-conditioned office to an air-conditioned truck, to the summer heat is a large swing in climate.
Thanks all for the replies. To answer some of the questions, data collected in Carlson Surveyor 2 using SurvCE5. All shots in sets are stored. Traverse is being run with prism poles not 3 sets of legs swapping the instrument out. The tribrach is solid, as are the legs. The tribrach is actually new, came with the new gun, and the release lever is screw locked in place, but it is solid. As set up, the gun returns properly to zero. The indirect is always within a few seconds of 180. We've used Survnet to analyze traverse quality and statistics, though it matches up well with hand calculations of internal angles. On one of the many trips back to re-turn angles to meet angular standards, where we used blunder detection in Survnet to help fund the most likely angles to check, the crew chief found that each angle turned mismatched the previous turn by 1 to 2 minutes. This has me thinking there must be some eccentricity in the horizontal circle of this particular instrument. I'm going to use some of the suggestions presented here for shooting sets with points every 60 degrees or so, then turning the tribrach 120 and checking each for each of the 3 positions. I'm hoping that will help find the eccentricity. Thanks for all the suggestions.
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Have this crew swap equipment (everything, not just the instrument) with another that performs well. Narrow the cause down to equipment or user error.
Have you checked the optical plummet? I had a new instrument once that came with a laser plummet and my partner ordered it with an optical plummet in the tribrach. I noticed right off that the optical plummet and the laser were aligned differently but was told by the dealer that the plummet in the tribrach would cause the laser to deflect and that we should only use the optical plummet in the tribrach. After busting a traverse twice and getting seemingly random errors all over the place, I sent the instrument back to the dealer and told them to remove the laser and replace it with an optical plummet in the alidade and remove the one in the tribrach. When the instrument came back, I proceeded to bust the same traverse a third time. Either the dealer failed to properly adjust the new optical plummet in the alidade or Fedex jarred it out shipping it back to us. Centering the plummet over a mark then rotating the alidade 180?ø would give a difference in centering of about 3/16". Because the direction of error changes for each setup it made for a crazy pattern of errors.
Mark Mayer, post: 441865, member: 424 wrote: Have this crew swap equipment (everything, not just the instrument) with another that performs well. Narrow the cause down to equipment or user error.
Yes, this is our next move.
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Stephen Ward, post: 441867, member: 1206 wrote: Have you checked the optical plummet? I had a new instrument once that came with a laser plummet and my partner ordered it with an optical plummet in the tribrach. I noticed right off that the optical plummet and the laser were aligned differently but was told by the dealer that the plummet in the tribrach would cause the laser to deflect and that we should only use the optical plummet in the tribrach. After busting a traverse twice and getting seemingly random errors all over the place, I sent the instrument back to the dealer and told them to remove the laser and replace it with an optical plummet in the alidade and remove the one in the tribrach. When the instrument came back, I proceeded to bust the same traverse a third time. Either the dealer failed to properly adjust the new optical plummet in the alidade or Fedex jarred it out shipping it back to us. Centering the plummet over a mark then rotating the alidade 180?ø would give a difference in centering of about 3/16". Because the direction of error changes for each setup it made for a crazy pattern of errors.
This instrument has a laser plummet and it appears to be adjusted perfectly. You can spin it 360 and it stays in the center of the mark.
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There are spots on this earth that are always in motion and I have found several.
One foremost point on a 400 acre survey was in the middle of an oil surfaced road at the top of very steep hill each way with a 48in red oak about 20ft away.
The only place to setup and see any distance both ways.
Never could double an angle there within 20sec.
Could not physically feel that slight amount of movement and I am sure that the breeze was rocking that tree enough to cause movement in the setup.
Using that point as the beginning and ending of the traverse resulted in an amazing coordinate closure.
Have had several points in the same traverse that acted the same and were probably due to similar or related movement in the setup.
We were attempting to align a railcar dumper that was being erected in Pine Bluff Arkansas and we were setting on a trivet on a concrete wall and the instrument would not stay level or on line.
We left that day with our egos bruised and were overloaded with many unanswered questions.
Starting out with the same task early the next day we found that the top of the concrete wall had a 0.45ft separation away from the rest of the structure.
Once the motor and mechanism to roll the railcar dumper had been placed on the concrete pad, the engineering failed to support the actual structure.
0.02