I have recently started on a new project and there is no record of any existing control points on the site. I am currently working with a Trimble R12i GPS which is fine for setting out the piles and drainage but I will need to use a total station for accuracy when we start the steel frame. How do I go about setting up a control network that I can use my total station with?
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Have a surveyor set a benchmark and some control points while they're at it you can reference from after with your total station for critical layout...?ÿ GNSS for not so critical if need be... but best use total station for all...especially if robotic total station for quicker 1 man layout.
Put in (at least) four of your own control points
Use your gps to record the best position you have for each.
Put your GPS away - you don't need it any more.
Preferably make a closed level run across your points.
Use your total station to observe a resection on three of the points.
Shoot the fourth as a check.
Re observe all points to tighten up the control.
Hold these values for the duration of the project <- this is the important bit
Observe as many new control points as you can.
Any time you are on site using your total station add more control points.
More control is good - you always need twice as much as you thing - and you can never have too much.
(well it works for me)
OK, since someone's going to point this out anyways, it might as well be me.
This is not a question that is easily answered on an internet forum, especially knowing nothing about the particular site you are discussing. Setting control, deciding upon an observation scheme, tying it to property boundaries, analysis and adjustment of the raw measurements, and publishing of final coordinates should be left up to someone with the proper credentials and experience. Especially if you are going to staking steel - there will be a maximum positional tolerance that dictates how the control network is run. Other staking tasks may change things as well.
It's not that it's impossible to learn about the subject online, it's just that it is far better (both practically and legally speaking) for the right person to take responsibility for it while showing you the process on site. On this forum you're likely going to get a wide variation of opinions on how to do this, each being a product of regional procedures and specific projects that the forum member has personally worked on.
Yeah, as someone will no doubt point out, sometimes small projects can be approached with a minimalist procedures, but that's pretty rare. And you still need someone with experience to recognize that situation.
If you have been given personal responsibility for establishing a control network integrating GNSS with total station (and possibly level) data, without understanding how to do so, that's a huge red flag that someone upstairs doesn't know what they are doing and/or is unaware of the consequences of doing it wrong. Don't let someone set you up for failure.
Most important : make SURE that the points selected for control cannot move. Also ensure with reflective targets that they are in positions where you will be observing close to square on to the target. One where you observe very obliquely is no good at all (apart from as a height CHECK if all else fails)
I've recently seen control points on:
1) fence posts where the fence is already leaning over
2) target on top of stack of 4 steel cabins (will go up and down with seaons according to temperature, may twist around slightly as sun heats one side of cabins and then the other during the day and the joining legs expand differently
3) target stuck to steel columns, where columns not yet grouted up and more beams still to erect.
When it comes to control, a good rule of thumb is if you have to ask questions about how then you should not be creating control. When you no longer have to ask questions, only then are you qualified to create the control.
@lurker?ÿ
Or maybe also know what questions to be asking, and know when you need to be asking them too....i.e. which phase of the project will overrun the initial control, and how you're going to transfer inside the structure once that phase is unfolding.
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I have a so many questions.?ÿ First one...is this a wide open site or are they tying into an existing building?
@jflamm?ÿ
Interesting. My first question was whether or not we were being trolled. If someone doesn't know the answer to the OP, they would be far better off tossing their equipment (no matter how expensive) in a river somewhere and paying a qualified person to do the job. I can guarantee it would be cheaper.
Simple answer: hire a surveyor to setup a baseline offset for building layout. It sounds like you don??t have the experience to establish that.
My first question was whether or not we were being trolled.
Me too...
&ct=g
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Just a simple question really. How is it this ??project?? was designed with zero control on the ground? It simply does not add up, designing anything with no way to relate it to the real world. What am I missing here.
OP says they are setting piles and drainage with his GPS - so they must have some form of control and calibration already in place...
Beware of the scale. GPS is using it, but you can't stake buildings' colums unless is set to 1
lmao. This is happening more and more. Not knowing any details in this particular case, but just last month had to talk a client through spending an unplanned 30k for a design survey for a development (that includes a 10 acre ??lagoon?) where everything to date had been designed off free lidar data from a state portal. The guy was about to fire me, was convinced I was trying to pull one over on him. Only after I had a?? diplomatic and long talk with his civil team did they finally call him and let him know that, yes, getting an accurate, on-the-ground survey was probably better than taking the chance on the stuff they ??thought? was good enough.
Wow.?ÿ Free Lidar data.?ÿ What could possibly go wrong with that?
diplomatic and long talk with his civil team
Oof. The civil team is the problem. Free LiDAR has its place in the project lifecycle (preliminary design), but designing an entire project off it is...almost always negligent.
spending an unplanned 30k for a design survey for a development
That's not quite chump change, but for what sounds like a good-sized development, that's small potatoes.
I don't know if I would be able to work with a civil team that doesn't care about having a good survey base for design, and resists telling the client that they need one.
@jitterboogie This is happening more and more.?ÿ This is no joke...we had a subconsultant on a large hydro job tell me he checked his data with google earth after I was finding all kinds of problems doing QC.?ÿ They are now black listed from anymore USACE projects.
