Setting house building corners with GPS

What do you mean "set building corners"???

I would not dream of setting building corners for construction with GPS. Maybe a rough layout.

Pad corners, yes.

Form board corners, maybe two. Then I would get the gun out, check distance on those two and check into property line and proceed to set the rest of the formboard corners with the gun.

My 2¢.

I would never use GPS to stake out a building. To my way of thinking, you are going to have to square up the building anyhow, why not just use the instrument?

> ...I would assume everyone would use GPS when there is a lot of room to play with on large lots; is this correct?

You are assuming that everybody uses GPS which would be false from the get-go.

"IF" I used GPS for staking, it would be for very rough staking... footers and basements maybe.

For nails in a footer for a foundation? I don't think so. But, that's just me... or maybe not just me.

Carl

I have used GPS to set corners and have had good success. My use of it has to do with a lot of things, clear skyview, amount of room I have to play with, geometry of 'birds'. I don't do it often though. Ct isn't built for to much GPS stakeout.

The way I see it, on every construction project there is a variable "positional error budget".

From the stake out, to the footer lay out, to the foundation, etc. a certain amount of error is going to accumulate and it would behoove the one person in the process with an understanding of measurement error to work in such a way to introduce as little error as situationally possible.

As far as I'm concerned, the only thing GPS is good for (at least here in the northeast) is setting aerial control. And that's only after multiple occupations of the same point, computing an average, and comparing to a fixed bench.

As-builts, maybe. Stakeout, nope.

-V

Rough building pad yes. Building set backs, yes. Building corners no. Unless they just want a starting point. Anything tight we would use our total station, and a peanut prism.

Would not trust the GPS, because all the houses around here have trees around them. Besides, my robot and I can stake house corners, footings, off-sets or whatever you want faster than any GPS. That robot is the best instrument man I have hired in twenty years. 🙂

We use GPS for excavating foundations, and get the robot out for anything that requires a tack.

November Foxtrot Whiskey!

Try reading Accuracy of OPUS solutions for 1- to 4-h observing sessions

"...Since 2002, NGS has been providing the GPS community with OPUS processing, free of charge. Among the limitations for using OPUS, the time duration of the GPS data set was always emphasized. A minimum of 2 h of data is recommended to obtain results sufficiently accurate for surveying applications. The results of this investigation indicate, when using 2 h of data, results in the north, east, and vertical (up) components have experimentally determined RMS errors of 0.8, 2.1, and 3.4 cm, respectively. Reducing the observation span to less than 2 h drastically increases uncertainties due to difficulty in fixing integer ambiguities as consequence of poor geometry and local atmospheric disturbances. NGS is currently trying to develop alternative software capable of reliably fixing integer ambiguities for time periods of 15 min and less."

Setting building corners using GPS.....
Your fired!,Atleast you would be if you worked for me. 🙂
Gee...and noone will hire me part-time even, because I'd make you punks look like crap.
Old School Stylz Rule 🙂

November Foxtrot Whiskey!

Perfect answer 🙂

> In the interest of not hijacking the "do you believe your data collector" thread I figured I would start a new one.
>
> Do you set building corners with your GPS? We do. We don't layout a lot of homes 1-3 per week in a few subdivisions that we platted; and we make all the checks we would normally make conventionally. I have never seen a problem (knocking on wood) but I would be curious to hear others opinions. If you think its crap I want to hear it and why?
>
>
> Thanks,
>
> Charlie
>
> PS: I was referring to smaller lots; our norm is .25 ac or less. I would assume everyone would use GPS when there is a lot of room to play with on large lots; is this correct?

Your P.S. worries me a bit - there is little room to play on a 0.25 acre parcel - using GPS for stakeout is almost asking for trouble...

And if you're checking things conventionally anyway, why even bother staking with GPS?

My answer to your question is yes, sort of.

I laid out 2 points of a gridline offset for a Lowes I was staking out - the site was huge and open with no concern for setbacks.

Once I had the 2 points in, I setup on one of them with a Robot, adjusted the distance of the backsight to match the gridline length, then turned a series of 90's, running a closed loop around the 4 main corners of the grid. Once I had checked my main 4 points, I began laying out the gridline offsets by occupying one point, setting 0 on a backsight, then staking distances on line. Lastly, we set up on each grid line, sighted the previous backsight, and checked 90 over to the corresponding grid point on the other side of the building.

[sarcasm]I use GPS to set anchor bolts as well...never had a problem[/sarcasm]

Depends on what kind of tolerance you are working with.

I use GPS for grading building pads and parking lots because the contract calls for +/- one tenth.

Setting actual building corners require a little tighter tolerance, so I wouldn't use it for that.

For clarification I was speaking about a 40x60 type envelope for a single family residence. I always viewed this as an application that was not for gps but based on our checks I am getting diagonals within .02' & ties to property corners within .03'. We recently laid out 13 houses in a subdivision (6 one day and 7 two weeks later) with GPS. I wanted to see how they held up to a conventional layout so I had the crew conventionally set property line-center line points with a Topcon and pull swing ties. The worst was .06 (had .5 feet on either side) with the norm around .02. Combine that with diagonals within .02' and I am really wondering why GPS isn't valid for this type of layout (checked with a chain). The switch to GPS layout intrigues/concerns me but to this point I have yet to see anything tell me it can't do it. My concern is that I have yet to hear someone say it can do it, including the salesman. I know this much my chrome clad can irrefutably prove any house we layout in our subdivisions.

Yeah, right and make sure you get it down on the grid. I gotta shake my head on this concept.

I am not there yet, I guess. Certainly not on commercial projects where I still have concrete contractors chewing my butt when their 'checks' witness a 10" error on a 100' column line (at least according to the instrument that's been bouncing around in the back of their rig for the last 3 weeks). On a residential house layout I might not be so leery since it is highly unlikely that anyone is checking your stuff anyhow, and where most 2x4s have a bigger degree or arch than any gps error ellipse. Besides all that, every other thread mentions doing redundant checks with a total station. If you're gonna do this, then why not just use the total station? If you have visibility for a sky signal than you probably have excellent conditions for a total station. Practically speaking it does not make sense to stake a residential structure.