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KevinFoshee
(@kevinfoshee)
100+ posts Member
Joined: 5 years ago
Posts: 124
December 7, 2018 7:17 am  

"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."

Just for the record, I have about 5 years experience with a Trimble S6 and 360 prism. Our traverses always closed good. 1:20,000 to 1:40,000 were common. I don't think that was his issue. On short sights, though, sighting the center of a prism pole can be an issue. We kept our level bubbles well adjusted.

Precisely sighting the center of the prism pole on short sights can be difficult.


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KevinFoshee
(@kevinfoshee)
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Posts: 124
December 7, 2018 7:21 am  

And just for the sake of covering all the bases:

You did convert your GPS control points from Grid coordinates to Ground coordinates. Right?


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aliquot
(@aliquot)
500+ posts Member
Joined: 7 years ago
Posts: 882
December 7, 2018 7:37 am  

Ahhh, now that I understand exactly what you did, two feet doesn't sound out of the ordinary. I would suggest not using bipods or a 360 prisim under such adverse conditions. You say under normal conditions your closure is as low as 1:20,000. That may be accurate enough for what you need, but that's really low for modern equipment. When you put more stress on your procedures by the conditions in the cave that's going to go down significantly.

Traversing with tripods seems to be out of fashion, but it will greatly increase your precision.  When I traverse with my 1990's conventional gun my absolute bottom is 1:60,000, but if I switch to bipods I am down near what you are getting. I have traversed in similar environments as your cave. It took two tries, and painstaking effort, but we were able to get 1:30000. The problem was the inordinate amount of time it took. It sounds like it may not be worth it for what you are doing.


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KevinFoshee
(@kevinfoshee)
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Joined: 5 years ago
Posts: 124
December 7, 2018 9:15 am  
Posted by: aliquot

Ahhh, now that I understand exactly what you did, two feet doesn't sound out of the ordinary. I would suggest not using bipods or a 360 prisim under such adverse conditions. You say under normal conditions your closure is as low as 1:20,000. That may be accurate enough for what you need, but that's really low for modern equipment. When you put more stress on your procedures by the conditions in the cave that's going to go down significantly.

Traversing with tripods seems to be out of fashion, but it will greatly increase your precision.  When I traverse with my 1990's conventional gun my absolute bottom is 1:60,000, but if I switch to bipods I am down near what you are getting. I have traversed in similar environments as your cave. It took two tries, and painstaking effort, but we were able to get 1:30000. The problem was the inordinate amount of time it took. It sounds like it may not be worth it for what you are doing.

aliquot,

I think you have confused me for the original poster.


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Norman Oklahoma
(@norman-oklahoma)
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Joined: 3 years ago
Posts: 3999
December 7, 2018 9:20 am  

I use a 360 prism for control and boundary regularly. I acknowledge that there is some small loss of precision because of it. But other items, such as centering error, ppm corrections, and even tripod stability are much greater concerns.    

"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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KevinFoshee
(@kevinfoshee)
100+ posts Member
Joined: 5 years ago
Posts: 124
December 7, 2018 9:30 am  

My comments about sighting the center of the pole are irrelevant since he was using a robot.

I would bet money on his level bubble being out of adjustment.


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David Livingstone
(@david-livingstone)
500+ posts Member
Joined: 8 years ago
Posts: 850
December 7, 2018 10:28 am  

Not very great test on my part, but I'm a new trimble robot user.  I tested our robot with tripods and tribrachs with regular prisms.  I carefully turned the angles 4 times with a 3 second Nikon gun.  Then let the robot turn the same set of angles 4 times all by itself.  Got within the same angle by 1 second.  Then with the 360 prism on the foresight. I got about 9 seconds different.  Not very exact test as might backsights and foresights were only about 150 feet.

Dave


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Rankin_File
(@rankin_file)
2,500+ posts Member
Joined: 8 years ago
Posts: 3534
December 7, 2018 11:48 am  

Given what has been posted so far, my initial go with Starnet would be fix the known control coords  YXZ-  angular error of 180 seconds zenith error 20 seconds, inst. centering error 0.005

tgt centering error 0.05

height error 0.05

and see what the residuals were on my angles- then start looking from there.

"Nothing quite says awesome like a bruised shoulder, the smell of gun powder, and a zombie hanging on your wall."
Youngest File-


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