[towerguy3]

I saw on Discovery Channel yesterday that GPS units are used to determine the straightness of the Burj Dubai as it grows. Small receivers are placed on the corners of the highest points and on the ground, and allowable deviation from "plumb" (a term for straight down as a pendulum will point straight down due to gravity) cannot be more than 7 centimeters.

Would GPS units be used to determine the straightness of Shangri-La (646 ft) and Calgary's Bow (850 feet) as they grow?

[mersar]

That does sound a little off, considering even military grade GPS has some margin of error to it. I'd expect if they did use a GPS system for that purpose it that it would be backed up by a more traditional system as well to ensure everything is correct.

[You Need A Thneed]

That does sound a little off, considering even military grade GPS has some margin of error to it. I'd expect if they did use a GPS system for that purpose it that it would be backed up by a more traditional system as well to ensure everything is correct.

I imagine they might use a total station that would have a GPS in it. I doubt they'd use solely a GPS to plumb the building. A good laser plumb or something like that would be more accurate.

[ReginaGuy]

I doubt it, they would most likely use a total station.

You can't use GPS for control surveys on buildings. GPS is fine for surveying large fields where you can get away with relatively low accuracy, but with structures, you should be accurate to the nearest millimeter, which isn't possible with GPS as far as I know.

GPS accuracy can be increased by using radio-type towers that send out a benchmark location to correct and refine the GPS signal, but it would probably be easier to just do it the old fashioned way :shrug:

I could be wrong, but I've never heard of something like this being done

[renthefinn]

AFAIK, GPS in military (US) applications is good to about 6 inches, which is not good enough for construction purposes. The EU were supposed to have a sattelite system running now similar to GPS I think it's called Gallileo, but I haven't heard much about it, so not sure what's up with that. Perhaps they have greater, and more freely availabe data?

[weezerfaninfreddy]

GPS has been used in construction for quite a while now. Most highway surveys including layout are done with something called Real Time Kinematic GPS. This can get you down to +- 1cm accuracy for the newer models I believe. THe equiptment I use was about +-5 cm. In terms of construction projects, most small projects are laid out with a hand tape and in some cases with a total station. mm accuracy is not really required since most construction workers won't achieve even 5mm of accuracy.

[renthefinn]

Ahh I didn't know they had anything that accurate yet, the most accurate I've used is to about +-1m, for basic survey.