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Can I do High rise stakeout (ftgs,cols,walls,slabs)using the latest GPS machine (which brand?) and obtain the same accuracy (+/- 5mm)of a Total station?
This Content Originally Published by a land surveyor to Land Surveyors United Network
perhaps you should be more specific
With my Robotic Total Station I can place on the ground: footings, Columns, walls...; on the forms: slabedges, cols, walls.... everything with good accuracy (5 mm more or less). My question:
Can I do the same with the latest GPS machine?. Thanks for asking.
Hi, I just want to share this doc.
"Advanced Surveying Control Services for Building the Vertical Cities.
Joël VAN CRANENBROECK, Switzerland"
Thanks for your reply. In my reply on April 29 I wanted to share a document that I believe can be the answer about this question, the name of the document is correct but I didn't put the link. This is the link
two of my friends are working at ground zero,one is doing tower four and one is on the freedom tower, they are working for the steel erector, they have been using gps, the General contractor has there own surveyor's, they are using traditional skyscrapper ( or high rise surveying procedure's , throwing the lines up from the street and also bucking in on target's( on other building')s.
They were usually hitting each others lines pretty good (no more than .05 difference) however , It's getting tougher and tougher ( once you get above 700feet). I know their up much higher on the freedom tower now. if you have a good gps system, you should be able to do the job,
try my method for high rise building it will works well
Hi Kadmous El Khatib.
How is that?.
Can you please elaborate your method in detail.
It's what we developed for the first time at Dubai for the Burj Khalifa. We introduced the concept of "Active GNSS Control Points". It's about screwing a GNSS antenna/receiver on top of a 360° reflector (or circular reflector if you can orient it properly). These "Active GNSS Control Points" can be easily placed around your total station and wherever you need to get good free station/resection. Now the key point is how to reach 5 mm accuracy and even better ? RTK will never deliver you such results on the spot, you need to filter and average and ... you need ambiguities fixed while on building top you have lot of obstructions. The best way is to post-process GNSS observables in PPK mode (Kinematic-on-the-fly). We reached that conclusion in Dubai as the chief surveyor was spending/wasting so much time to de-select satellites and try hard to get ambiguities fixed. PPK in combined mode (forward/backward) helps a lot to deliver precise coordinates ... when it's possible. Over an hour, you will have enough to get 45%-65% of good results. The other remaining are just unfixed because multi path's and obstructions. Hope it helps ?
Now what kind of GNSS receiver/antenna you do need ? We are very much happy with the SinoGNSS T300 of ComNav Technology Ltd.Shanghai as they are developing their own OEM boards (like NovAtel and Trimble and Septentrio) and to start logging GNSS measurements it's one button operation. You even don't need a field book as you can even use your smartphone (Android) or any mobile with the new T300 Plus (web server integrated). Their receivers are very much robust and pricing is soft ;-) ... which is a important point when contractors are at ease to squeeze everything ! For post-processing in PPK you can use RTK-LIB that is Open Source free software. We compared RTK-LIB results with LGO and they matched perfectly (below the mm). Hope it helps ?
My response would be, if you can achieve centimeter accuracy, with random error, on top of a highrise, which is constantly moving anyway, and leaning from the sun, then that would be "good enough" to check in your grid lines from below. The key to high rise, which allows out of plumb to certain tolerances, is repeatability, that is making sure the grid lines from the floor above matches the floor below, usually try for 3 mm but craftsmen will live with 6 as long as you are not accumulating error. Therefore, using both RTK for top control, and conventional (or laser plumb) to bring it down works as long as you check between floors. If steel, the iron structure is usually punched before the sheeting is welded down, then again when the sheeting is welded down for cutting openings, and finally on the slab. Concrete is similar.