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Norman Oklahoma
(@norman-oklahoma)
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December 6, 2018 10:39 am  
Posted by: Totalsurv
Posted by: Bill93

 And some people who didn't read the word CAVE in the OP.

I read it fine and I also read that a 0.5 second gun was used. If a 0.5 second gun was used on this traverse I suspect it may have been used to attain a certain level of accuracy. If that is the case a 2' closure is probably unacceptable. If it just happens to be their everyday gun then fine. Perhaps if the OP could give an idea of what the survey is for?

This "misclosure" doesn't interest me much. See me once the thing is put together and the residuals determined. Closures are so 20th century.  

It is just as likely that they were using a 0.5" gun because that is their daily driver. But in order to get 0.5" angles out of a 0.5" gun you are going to need to be setting it, and the targets, on concrete pillars. Setting it on common tripods, and over chalk marks, as pictured, says more about the required precision that the choice of instrument.      

This post was modified 3 days ago by Norman Oklahoma

"Convention is like the shell to the chick, a protection till he is strong enough to break it through." Learned Hand


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aliquot
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December 6, 2018 10:47 am  

Traverse adjustments are intended to correct for random error. 2' sounds like more than random error to me. Even with your less then ideal circumstances you should be able to do much better then that. Are you confident in in the coordinates for your start and ending? I would be looking for a blunder or an overlooked systematic error, rather than an adjustment, but running through adjustment procedures might help you find it.


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Totalsurv
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December 6, 2018 10:49 am  
Posted by: Norman Oklahoma
Posted by: Totalsurv
Posted by: Bill93

 And some people who didn't read the word CAVE in the OP.

I read it fine and I also read that a 0.5 second gun was used. If a 0.5 second gun was used on this traverse I suspect it may have been used to attain a certain level of accuracy. If that is the case a 2' closure is probably unacceptable. If it just happens to be their everyday gun then fine. Perhaps if the OP could give an idea of what the survey is for?

This "misclosure" doesn't interest me much. See me once the thing is put together and the residuals determined. Closures are so 20th century.  

It is just as likely that they were using a 0.5" gun because that is their daily driver. But in order to get 0.5" angles out of a 0.5" gun you are going to need to be setting it, and the targets, on concrete pillars. Setting it on common tripods, and over chalk marks, as pictured, says more about the required precision that the choice of instrument.      

It would interest me in this case considering the nature of the traverse conditions and the probable limits on redundancy.


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Bill93
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December 6, 2018 1:22 pm  

He said "I would like to get it within 0.25' spatially" so we know it isn't expected to be super good.

They have multiple short legs in the traverse, as small as 20 ft.  Centering error, even with McMillan precision, can account for much of the 2 ft closure after propagating azimuths through a long traverse.  The calculation I showed in my first post supports that based on centering that is better than can be expected here, as probably indicated by the 0.05 ft discrepancies in repeated distance measurements. 

The analysis and any adjustment MUST consider probable centering error if it is to be meaningful, and Star*Net can do that easily.  He doesn't seem to have (or have used) a program to do least squares.  It's too big for the demo mode of Star*Net.  Are there other inexpensive options for him to get least squares capability?


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Rankin_File
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December 6, 2018 1:26 pm  

Mutli-track prisms, bipod foresites & Backsites, 20 foot legs, you'll accumulate error quick. Star net will help you sort it out, if you provide realistic error estimates.

 How many sets were you turning? FWIW, I don't traverse or side tie with a 360 or multi-track.

"Nothing quite says awesome like a bruised shoulder, the smell of gun powder, and a zombie hanging on your wall."
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Norman Oklahoma
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December 6, 2018 2:35 pm  
Posted by: Totalsurv

It would interest me in this case considering the nature of the traverse conditions and the probable limits on redundancy.

It's not likely a 2' error. It's probably a 0.05' error in a short backsight propagated by a long traverse. The misclosure is meaningless until this data is simultaneously adjusted and analysed.  

"Convention is like the shell to the chick, a protection till he is strong enough to break it through." Learned Hand


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A Harris
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December 6, 2018 4:32 pm  

The worst errors are not zeroing on the BS and inputing wrong BS point numbers.

I always use tripod and tribrach and tilting prism sets for BS and FS and it really helps closure.

This is my goto traverse analysis proceedure

RPLS NE Texas
d[-_-]b


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David Livingstone
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December 6, 2018 4:44 pm  

What bothers me is 0.05’ on distance. Even not being careful should get better than that.  I also agree short sights will cause problems. It’s in a cave what else can you do. Interesting job thanks for the pics. 

Dave


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Paul in PA
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December 6, 2018 6:35 pm  

There is no good way to adjust a point to point traverse. If you had a point outside the cave, then entered the cave and came out at another point you should be able to have an azimuth in and an azimuth out. It is correct to hold both azimuths and adjust and a good adjustment can show you where the primary source of error is. To be reasonable you cannot hold for a maximum of 0.5"angular error as it will adjust all the good angles also.  I would suggest allowing 5". 

Are your traverse points on the floor or the ceiling? How precise were your plummet sights? Coming out flat on elevation and distance says to just turn the whole traverse, point to point and call it good until you find otherwise.

Paul in PA


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Bill93
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December 6, 2018 7:12 pm  

Hold 5 seconds on an angle with a 20 ft leg? ?


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Dave Karoly
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December 6, 2018 7:57 pm  

Yes the 0.05 miss on a check back is concerning. Should be no more than 0.01, maybe 0.013 on the far outside.

Caves can have weird refraction too.

While we are on the subject of hard work, I just wanted to tell you that I am a man who likes hard work.
I was born working and I worked my way up by hard work.
I ain't ever got no where, but I got there by hard work.
Work of the hardest kind.
I been down and I been out
I been disgusted I been busted and I couldn't be trusted.
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Paul in PA
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December 6, 2018 10:31 pm  

Bill93,

A minute allowable error might be more appropriate. But even at 5", if the adjustment throws the 5" into one specific angle you will know where he problem was. It is better to give the LS program some room to work in.

Paul in PA

This post was modified 3 days ago by Paul in PA

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Totalsurv
(@totalsurv)
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December 6, 2018 11:51 pm  
Posted by: Norman Oklahoma
Posted by: Totalsurv

It would interest me in this case considering the nature of the traverse conditions and the probable limits on redundancy.

It's not likely a 2' error. It's probably a 0.05' error in a short backsight propagated by a long traverse. The misclosure is meaningless until this data is simultaneously adjusted and analysed.  

Yes but the misclosure has been the starting point for him to know he has a problem. I also question whether there is enough redundancy, the OP has not specified.

It also looks from the pictures that a 360 prism on a pole may have been used for the traverse. From reading other posts here it seems that traversing with a Trimble using Autolock and a 360 is a bad idea.

I suggest there may be a problem here with procedures that are unlikely to be fixed by a LS adjustment.

This post was modified 2 days ago 4 times by Totalsurv

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Jake1522
(@jake1522)
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December 7, 2018 6:23 am  

All-

Thanks for your input and ideas.  This work was all done with our daily driver along with a 360 prism pole.  The accuracy that I got out of it was good enough for what i needed it for. Looking back there are a few things that I should have done to get better results.  I knew what most of these things were going in but it was a test to see "how close" I could get without trying too hard.

Next up we are going to scan this cave with the new Leica 360 scanner.  Supposedly this scanner will tie to itself with auto registration.....Like doing a resection using 1000s of points. Then you adjust the cloud to the control.  Obviously I'll used the control outside the cave to hold and then see how it fits the adj Trav control.  The dealers have told me they did about 120 scans and closed on the original scan by 0.02'.  I'm super interested to see how this turns out and will report back to you all. 


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Norman Oklahoma
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December 7, 2018 7:08 am  

I don't do scanning - yet - but I'm close to someone who does. I'm told that the autoregistration works best with well defined shapes. You may not get good results with cave walls alone. 

"Convention is like the shell to the chick, a protection till he is strong enough to break it through." Learned Hand


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