I am building a metal building on my property and I need to set 6 concrete piers in a rectangle 24' by 50'. One on each corner and one at each midpoint between the corners on the long side. This will butt up to an existing building. A lean to of sorts off the side of it.
This is going to be a shed to park my equipment under and is no where near any boundaries, and I have no building codes to follow. I am the one going to be welding the building up so if I screw up the placement of them it is just my problem. The piers will be roughly 2' square but once I set the welding plates in the wet concrete they are not much bigger than the I beams and thus need to be placed accurately within an inch or so.
I have built things like this in the past and used a tape measure and measuring diagonals to ensure it is square. It works but is time consuming and requires a helper to hold the tape and I am by myself the next couple of days and would like to get this done.
I was thinking of staking this out using my RTK. It is simple enough to build the rectangle and stake out the points but three of them are going to be less than a foot away from a 15' tall metal building. I know this is not good for the GPS signal and multi path but I really have no experience with it and the effects. I typically do all my RTK work in the oilfield in the middle of nowhere with no interference to worry about.
Will this work or will the building mess me up? When you get this kind of interference do you lose signal completely or does it just foul up your accuracy and you don't even know it is happening? Other than this building it is flat as a pancake with no trees or interference in the area.
There is absolutely no way I would trust an RTK position 1 foot from a 15 foot tall metal building. Well actually, I wouldn't trust it against a brick building for that matter.
James
Maybe it work. Probably would if you had the Javad system.
How about:
Stake it carefully, with GPS.
Then, use a rolo tape to check it? (bad joke!)
Then use a real tape, to double check and tweek it?
Getting stuff close is time consuming. Use GPS for that.
Then, tweek it all with a tape. Now you have what you really need. Take a few pics, Label the GPS shots with say, red paint. And, the tweeked and corrected ones in blue flagging.
Then you can quantify it.
That is the REAL problem with RTK... you don't have a 100% reliable mechanism to quantify your errors.
With RTK GPS, here are 2 basic assumptions.
The points are GOOD. This means within 0.10 to 0.20' Then, spend more time, and reshoot them, and now you start developing error ellipses. (quantifying the error)
OR due to multipath, or such, you are within 0.10' to 10 feet.
So, double shoot, and remove the possibility of multipath. We still have an error potential of 0.10' per shot. (it is usually a little better than that, BUT there are times in the day, when stuff is like that) Due to Sat Geometry etc.
N
> There is absolutely no way I would trust an RTK position 1 foot from a 15 foot tall metal building. Well actually, I wouldn't trust it against a brick building for that matter.
>
> James
If I do it I can verify it with a tape or multiple measurements I guess I was just wondering if it might work or if there was no point in even trying. All I concerned with is the X,Y. I plan on using a rotary laser to get the grade right.
I have a 16' prism pole, so I was thinking of getting up there. No more multipath.
I think the tape is the best tool for the job. How much does the RTK reading wander around while held on one spot? Probably more than you'd like. And with a likely reflection problem?
For what you are doing it could work, can you set the back corners and mid points with GPS then just pull a tape to the corners near the building?
What will happen when you work close to the building your V and H precision will go up, it might go up so much you will lose fix and be in float mode. You can try different times of the day to set the corners near the building the Satellites may be in a better position to keep the V and H down and fixed.
I would never set someones building corners with GPS I would use a total station if you have one or can borrow one. Since you are building it, build and stake it which every way you feel is best for yourself.
I wouldn't waste the time to set the GPS up.
Use large nails or rebar to hold the far end of the tape. Start parallel to the existing building and set the end points of the first wall. Using two tapes connected to opposite ends of the first wall pull the building length on one and the diagonal on the other and cross them where the numbers meet, now you have three corners. Now pull the diagonal with the first tape and the building length on the second tape and you should have all four corners. Check the length of the fourth wall of the building and adjust if necessary. Set up batter boards outside of the work area so that you can quickly reestablish the building corners with string lines and a plumb bob when you need to position the plates.
:good:
> I wouldn't waste the time to set the GPS up.
>
> Use large nails or rebar to hold the far end of the tape. Start parallel to the existing building and set the end points of the first wall. Using two tapes connected to opposite ends of the first wall pull the building length on one and the diagonal on the other and cross them where the numbers meet, now you have three corners. Now pull the diagonal with the first tape and the building length on the second tape and you should have all four corners. Check the length of the fourth wall of the building and adjust if necessary. Set up batter boards outside of the work area so that you can quickly reestablish the building corners with string lines and a plumb bob when you need to position the plates.
I agree, it seems better and faster. If you were talking about a 300' x 200' building, I would use a total station, but...
If you are trying to play with the RTK, using it to set a general location might make things easier, but probably not faster.
don't do it.....GPS is ok for the concrete, but even for that you want to take the elevations off the existing FF of the existing BLDG some other way. I would not trust it for the plates. Just use a tape.
You are spending your own money on materials, spend a couple of more bucks and get bigger plates. Seems like the wrong thing to be cutting back on.
I have never tried it against a metal building but if it was a solid tree/brush line, the points seem to be off perpendicular to that line.
If you set the 3 points against the building and the 3 points away from the building, it would be easy to measure from the far ones to the close ones to verify. If it was the only tool I had to use, I would set all 6 points and check the dimensions with a tape, including diagonals.
James
How about a laser messure. I find them excellent, can be put on a camera tripod and are not that expensive. Use it in the evening if you can't see the dot though the tripod helps a lot.
Using A Tape Is Too Time Consuming For 6 Points?
Get over it. It is less work than getting your GPS base right in the first place.
Paul in PA
> You are spending your own money on materials, spend a couple of more bucks and get bigger plates. Seems like the wrong thing to be cutting back on.
The plates are good and heavy duty. They are 1/2" thick with six Nelson studs. Strength wise they are all there they just need to be placed in the right spot.
> How about a laser messure. I find them excellent, can be put on a camera tripod and are not that expensive. Use it in the evening if you can't see the dot though the tripod helps a lot.
I am using a rotary laser to get the forms all level. I don't have a laser measure. This is my project at my place and I am trying to do it with the tools I have.
Using A Tape Is Too Time Consuming For 6 Points?
> Get over it. It is less work than getting your GPS base right in the first place.
>
> Paul in PA
I kind of see your point. Setting up the GPS and double checking things takes time. I am not trying to be lazy and look for the easy way out.
My hesitation in using a tape is for several reasons.
1) I already dug the large holes alongside the existing building. These are easy to locate as they are as close to the building as you can get and one on each corner and one in the middle. In hindsight I probably shouldn't have done this first as now I have large holes where the points are which makes it difficult to measure with a tape without help. I should have put a large nail or rebar at these corners and measured to get the other corners.
2) I am doing this as a project at my house in my time off. I don't have any help here. The GPS route seems easier for one person to do than tapes because I don't have help to hold the other end.
3) The measurements / marks will need to be placed and removed several times. I need initial marks to know where to dig the holes. If it is a pin or strings crossing they will need to be removed so I can dig and build forms and then pour concrete. I will then need to be able to quickly relocate these points once the concrete has been poured to set the plates. This in particular is where I thought the GPS would be ideal - to quickly set the plates in the wet concrete. Heck even if I don't use the GPS for the three alongside the building I thought of shooting in the three far piers once located and then using the GPS to at least place those three in the concrete.
> I am using a rotary laser to get the forms all level. I don't have a laser measure. This is my project at my place and I am trying to do it with the tools I have.
Yes I see. I'm a bit tool crazy 🙂 I actually have 2 (I lost it and had to buy another). I am sure though it would help with the construction of your building.
Before I bought a total station, I used it to do a plan of my property, using triangulation/trilateration! Now I just use it for measured building surveys and general stuff.
If I had to buy again I would spend a bit more and get one with a built in spirit level, and maybe a bit more distance 🙂
> The plates are good and heavy duty. They are 1/2" thick with six Nelson studs. Strength wise they are all there they just need to be placed in the right spot.
My mistake, I thought they were flat plates that you were going to be welding to.
