Hello,
I was wondering if anyone knows about the accuracy associated with steep angled surveying. I have a situation where the contractor is required to install a control network from known points at approx +10m above ground level (where the new control network is to be installed). I'm currently working for the client & I have a few years surveying experience & I learned that steep angle surveying is to be avoided (however I didn't learn any specifics for clarification). The work that is being done on my job has incredibly tight tolerances, so the setting out & surveying needs to be accurate.?ÿ
I have checked on CAD with a rough sketch and the sighting angle will be approximately 41 degrees. I have done some research but am struggling to find any information on the subject, hopefully someone here can shed some light.?ÿ
For reference, the contractor is using a Trimble S5 (5" angular error), & a mini prism with 0mm offset.?ÿ
Any help would be greatly appreciated, this is a bit of a stab in the dark. Also if you have any references for me that would also be great (so I can back my points up)
Thanks,
Rory
Nodal prisms will help, but I don't know if this is your magic bullet.
Many surveyors don't use/never heard of nodal prisms, which is surprising to me.
I would think they would be the majority of prisms out there, but not so much.
https://www.surveying.com/product/62-mm-nodal-point-prism-assembly/
Not sure about newer gear, but Leica/Wild had their own method of measuring prism constants, offsets, etc.
If I remember correctly, their method was essentially the opposite (or some strange way) of every other manufacturer.
I always had to refer back to the prism offset diagram to make sure everything was set correctly.
I recommend not mixing prism types with different offsets, etc. if possible; you'll save yourself a ton of headaches.
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This website graphic shows how non-nodal prism offsets affect the vertical too, and claim 0mm offest perform the worst for precision work, and show why:
https://www.linkedin.com/pulse/nodal-prism-targets-explained-heath-thompson
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Besides having the correct vertical angle turned and the correct distance returned, which the nodal prism helps, the operator needs to be aware of auto corrections being made by the instrument's compensator. He may turn a specific angle for stake out while the scope is roughly oriented towards the horizon, but when looking down or up at a steep angle there will be trunnion axis correction applied and the operator will need to re-turn the desired angle.
Make sure you run check & adjust on the instrument. Compensator, collimation & trunnion axis at minimum. Tribrachs too.
If you have the ability to resect from the published control, that will make things a lot easier.
As mentioned, nodal prisms are crucial, make sure that you still point them to the instrument for best accuracy.
Not sure about newer gear, but Leica/Wild had their own method of measuring prism constants, offsets, etc.
Leica considers -34.4mm to be the equivalent of zero offset, so that value must be added to the offset printed on the prism.
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If you really want to know what sort of accuracy you can achieve with the project and gear that you have been handed, this sort of scenario is exactly what the PreAnalysis function in StarNET was designed for. That's what I use for designing control networks and observation schemes for monitoring projects, or for any other oddball scenarios.
It does require the operator to enter in ALL the correct values for standard errors, and to have a pretty good idea where the new points and total station will be during the process. But if you do that part correctly, you can really dial in your procedures and be confident in the final values of the new control. Keeps you from going overboard too.
(I really like having a camera in the scope for this sort of work, so I'm not having to fiddle with a right-angle eyepiece, and so I can zoom in on points that are flat targets as opposed to prisms. Just throwing that out there since there are some steep angles involve.)
@rover83?ÿ
I looked into getting a right angle eyepiece about a month ago and was a bit surprised at the $735 price: Trimble P/N: 78500007 (S Series 90 Degree Eye Piece).?ÿKit contains 90 degree eyepiece, counterweight, and protective case.
Worked with a guy that wanted to "resection in" every chance he could. Didn't take notes, didn't check to BM, and didn't set new control points on these occasions. He flubbed something one time on a topo set up and was told if he couldn't resolve it, he'd have to go reshoot it on his own time. After he reshot the whole site, he never resectioned again, and his newfound affection for field notes was born (and they were meticulous).
Control surveying is a lot of fun, especially when you get the chance to really make your gear do its thing and test its limits. That's usually about the time the field staff figure they better check their gear for adjustment.?ÿ
D'oh?!
There are methods for replicating horizontal control grids vertically over hundreds of feet for high rises, etc. Traversing in from the ground can work, but is not my preferred method. The reality is that unless you close your traverse and then do some analysis of the traverse, you do not really know how well you did.?ÿ
Of course, once you do that you might realize that your incredibly tight tolerances are not achievable with your current set up, at least not a 95% confidence level.
I looked into getting a right angle eyepiece about a month ago and was a bit surprised at the $735 price: Trimble P/N: 78500007 (S Series 90 Degree Eye Piece).?ÿKit contains 90 degree eyepiece, counterweight, and protective case.
That is pretty reasonable. Topcon was more than that when I last looked, and I believe Leica was as well. How much will it cost if you mess it up because you do not have the right tool? You aren't buying the tool, are you?
...he'd have to go reshoot it on his own time.
That would get you sideways with a few government organizations around here...
...he'd have to go reshoot it on his own time.
That would get you sideways with a few government organizations around here...
I would hope so. That would get you sideways with anyone with the least bit of interest in taking responsibility for the work of the team they supervise.
If a crew leader isn't taking notes, and their supervisor doesn't address the problem and take steps to fix it, and then something goes wrong, that's ultimately on the supervisor. There's a sliding scale of responsibility depending on where you are in the food chain and firm-specific job classifications and such, but the buck stops with the person who is in responsible charge.
If someone's not up to par, and we don't remedy the problem through training or mentorship - or sending that individual along their way - that's on us. Fix the problem, but don't ask someone to work without pay. It's not only crap leadership, it's almost always illegal.
If the guy hadn't been trained, then yeah it's not his fault.
?ÿIf he had been taught how to do it and ignored instructions, it would be fair for him to redo it off the clock. Like already said, the rules probably din't allow the fair solution.
At the time of the incident (many years ago), that guy probably had 25-30 years of survey experience, and had been with the company for some time. We were all aware of the company protocol/standards, we were all trained and knew what was expected of us, and he had been warned about deviating from the standards in the past.
Seemed to me he got off light, learned a valuable lesson, and came out of the situation with a better outlook.
How would you guys have handled it?
At the time of the incident (many years ago), that guy probably had 25-30 years of survey experience, and had been with the company for some time. We were all aware of the company protocol/standards, we were all trained and knew what was expected of us, and he had been warned about deviating from the standards in the past.
Seemed to me he got off light, learned a valuable lesson, and came out of the situation with a better outlook.
How would you guys have handled it?
If he'd been with the firm that long, had been warned before about not taking notes, yet everyone was aware that he still was not taking notes, the biggest question is: why was he still with the firm at the time of this latest screwup?
If management didn't want to fire him for previous screwups, I'm going to assume that firing is out of the question this time around. I would have had him re-do that work and get paid for every minute of it.
Then I would have demoted him. No more running crews for a while, his new crew leader will be in charge of training him on how to take notes, and only when the crew lead and his supervisor are satisfied with his note-taking will he be reinstated as chief. That directly addresses the problem. Making him work without pay does not, and is of dubious legality to boot.
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I've been removed from a position of responsibility because I screwed up. I've removed others when they screwed up. The true test of an employee is whether they can learn, grow, take direction, and correct themselves when given the opportunity.
But some employees are liabilities rather than assets. If we willingly choose to employ a liability, and repeatedly refuse to let them go, we better be willing to take the hit when things go south. They may be bad at their job, but we hired 'em.
Leica considers -34.4mm to be the equivalent of zero offset, so that value must be added (note the effect of addition of a negative number) to the offset printed on the prism [when using a Leica prism with another manufacturers EDM].
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If the guy hadn't been trained, then yeah it's not his fault.
?ÿIf he had been taught how to do it and ignored instructions, it would be fair for him to redo it off the clock. Like already said, the rules probably din't allow the fair solution.
Might be "fair" but if dude is doing work for you, you have to be paying. What happens if he gets hurt, is he "on the clock" then?
Fair=Supervisor has to go out and follow around and advise dude while he does the work. Both get paid, and both hate the experience so much that neither repeats it.
@rover83 Yeah Party Chiefs are a dime a dozen. Just fire him and run down to the employment office and pick up a new one.
20 years ago it was tough to find rear chainmen.
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